Lesson 09: Operations on XML Elements

	Operations on XML Elements

Fundamental Operations

Introduction

So far, to create an XML element, we were directly typing in a file. When such a file had been created and saved, it was ready to be processed. Here is an example of a file named videos.xml:

<?xml version="1.0" encoding="utf-8" ?>
<videos>
  <title>The Distinguished Gentleman</title>
</videos>

In some applications, you will want the user to provide you with the necessary value(s) to create an element. Fortunately, the XmlDocument, the XmlNode, and the XmlElement classes provide all the necessary properties and methods to perform the routine operations of an XML file, an element, or a node. The operations include locating a node, adding a new element, or deleting a node.

Before performing an operation, you will usually need to decide in what section of the file you want the action to be applied. As it happens, you have on the root node, on a particular node inside the document, on the parent of a node, on a sibling of a node, etc. To get to a node, you will usually first get a reference to its XmlElement object. To do this, you can declare an XmlElement variable and initialize it with that reference.

Practical Learning: Introducing operations on XML Elements

Start Microsoft Visual Basic and create a new Windows Forms Application named SolasPropertyRental1
To add a new form to the application, in the Solution Explorer, right-click SolasPropertyRental1 -> Add -> Windows Form...
Set the Name to Tenants and click Add
From the Toolbox, add a ListView to the form

While the new list view is still selected, in the Properties window, click the ellipsis button of the Columns field and create the columns as follows:

(Name)	Text	TextAlign	Width
colAccountNumber	Account #		65
colFullName	Full Name		120
colMaritalStatus	Marital Status		85
colPhoneNumber	Phone #	Center	85

Design the form as follows:

Control	Text	Name	Other Properties
ListView		lvwTenants	Anchor: Top, Bottom, Left, Right FullRowSelect: True GridLines: True View: Details
Button	New Tenant...	btnNewTenant	Anchor: Bottom, Right
Button	Close	btnClose	Anchor: Bottom, Right

Right-click the Tenants form and click View Code

Import the System.IO and the System.Xml namespaces:

Imports System.IO
Imports System.Xml

Public Class Tenants

End Class

Just above the End Class line, define a new procedure as follows:

Private Sub ShowTenants()
    Dim Filename As String = "C:\Solas Property Rental\tenants.xml"
    Dim docTenants As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        lvwTenants.Items.Clear()

        docTenants.Load(Filename)
        Dim TenantElement As XmlElement = docTenants.DocumentElement
        Dim ListOfTenants As XmlNodeList = TenantElement.ChildNodes

        For Each Node As XmlNode In ListOfTenants
            Dim lviTenant As ListViewItem = New ListViewItem(Node.FirstChild.InnerText) ' Account Number

            lviTenant.SubItems.Add(Node.FirstChild.NextSibling.InnerText) ' Full Name
            lviTenant.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.InnerText) ' Phone Number
            lviTenant.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText) ' Marital Status
            lvwTenants.Items.Add(lviTenant)
        Next
    End If
End Sub

In the Class Name combo box, select (Tenants Events)

In the Method Name combo box, select Load and implement the event as follows:

Private Sub Tenants_Load(ByVal sender As Object, _
                             ByVal e As System.EventArgs) _
                             Handles Me.Load
    ShowTenants()
End Sub

To add another form to the application, in the Solution Explorer, right-click SolasPropertyRental1 -> Add -> Windows Form...
Set the Name to TenantEditor and click Add

Design the form as follows:

Control	Text	Name	Properties
Label	&Account #:
MaskedTextBox		txtAccountNumber	Mask: 00-00-00 Modifiers: public
Label	&Full Name:
TextBox		txtFullName	Modifiers: public
Label	Marital Status:
ComboBox		txtMaritalStatus	Modifiers: public Items: Single Widow Married Divorced Separated
Label	&Phone #:
MaskedTextBox		txtPhoneNumber	Mask: (999) 000-0000 Modifiers: public
Button	OK	btnOK	DialogResult: OK
Button	Cancel	btnCancel	DialogResult: Cancel
Form			AcceptButton: btnOK CancelButton: btnCancel FormBorderStyle: FixedDialog MaximizeBox: False MinimizeBox: False ShowInTaskbar: False

To add a new form to the application, in the Solution Explorer, right- click SolasPropertyRental4 -> Add -> Windows Form...
Set the Name to RentalProperties and press Enter
From the Toolbox, add a ListView to the form

While the new list view is still selected, in the Properties window, click the ellipsis button of the Columns field and create the columns as follows:

(Name)	Text	TextAlign	Width
colPropertyCode	Prop Code		65
colPropertyType	Property Type		85
colBedrooms	Bedrooms	Right	65
colBathrooms	Bathrooms	Right	65
colMonthlyRent	Monthly Rent	Right	75
colStatus	Status		65

Design the form as follows:

Control	Text	Name	Other Properties
ListView		lvwProperties	View: Details GridLines: True FullRowSelect: True Anchor: Top, Bottom, Left, Right
Button	New Property...	btnNewProperty	Anchor: Bottom, Right
Button	Close	btnClose	Anchor: Bottom, Right

Right-click the Tenants form and click View Code

Import the System.IO and the System.Xml namespaces:

Imports System.IO
Imports System.Xml

Public Class RentalProperties

End Class

Just above the End Class line, define a new procedure as follows:

Private Sub ShowProperties()
    Dim DOMProperties As XmlDocument = New XmlDocument
    Dim Filename As String = "C:\Solas Property Rental\properties.xml"

    If File.Exists(Filename) Then
        lvwProperties.Items.Clear()

        DOMProperties.Load(Filename)
        Dim RootProperty As XmlElement = DOMProperties.DocumentElement
        Dim ListOfProperties As XmlNodeList = RootProperty.ChildNodes

        For Each Node As XmlNode In ListOfProperties
            Dim lviProperty As ListViewItem = New ListViewItem(Node.FirstChild.InnerText) ' Property Code

            lviProperty.SubItems.Add(Node.FirstChild.NextSibling.InnerText) ' Property Type
            lviProperty.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.InnerText) ' Bedrooms
            lviProperty.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText) ' Bathrooms
            lviProperty.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Monthly Rent
            lviProperty.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Status
            lvwProperties.Items.Add(lviProperty)
        Next
    End If
End Sub

In the Class Name combo box, select (RentalProperties Events)

In the Method Name combo box, select Load and implement the event as follows:

Private Sub RentalProperties_Load(ByVal sender As Object, _
                                      ByVal e As System.EventArgs) _
                                      Handles Me.Load
    ShowProperties()
End Sub

To add another form to the application, in the Solution Explorer, right- click SolasPropertyRental1 -> Add -> Windows Form...
Set the Name to PropertyEditor and click Add

Design the form as follows:

Control	Text	Name	Properties
Label	Property Code:
MaskedTextBox		txtPropertyCode	Mask: 000-000 Modifiers: Public
Button	OK	btnOK	DialogResult: OK
Label	Property Type:
ComboBox		cbxPropertyTypes	Modifiers: Public Items: Unknown Apartment Townhouse Single Family
Button	Cancel	btnCancel	DialogResult: Cancel
Label	Bedrooms:
TextBox	0	txtBedrooms	TextAlign: Right Modifiers: Public
Label	Bathrooms:
TextBox	0.00	txtBathrooms	TextAlign: Right Modifiers: Public
Label	Monthly Rent:
TextBox	0.00	txtMonthlyRent	TextAlign: Right Modifiers: Public
Label	Occupancy Status:
ComboBox	Unknown	cbxStatus	Modifiers: Public Items: Unknown Available Occupied Needs Repair
Form			AcceptButton: btnOK CancelButton: btnCancel FormBorderStyle: FixedDialog MaximizeBox: False MinimizeBox: False ShowInTaskbar: False

To add a new form to the application, in the Solution Explorer, right-click SolasPropertyRental1 -> Add -> Windows Form...
Set the Name to RentalAllocation and click Add

Design the form as follows:

Solas Property Rental: Rental Allocation

Control	Text	Name	Other Properties
Label	Rent Allocation		AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft
Label	Allocation Code:
MaskedTextBox		txtAllocationCode	Mask: 0000-9999 Modifiers: Public
Label	Date Allocated:
DateTimePicker		dtpDateAllocated	Format: Short Modifiers: Public
Label	Tenant		AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft
Label	Property		AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft

Label	Account #:
MaskedTextBox		txtTenantAcntNbr	Mask: 00-00-00 Modifiers: Public
Label	Property #:
MaskedTextBox		txtPropertyCode	Mask: 000-000 Modifiers: Public
Label	Tenant Name
TextBox		txtTenantName	Modifiers: Public
Label	Property Type:
TextBox		txtPropertyType	Modifiers: Public
Label	Marital Status:
TextBox		txtMaritalStatus	Modifiers: Public
Label	Monthly Rent:
TextBox		txtMonthlyRent
Label	Allocation Evaluation		AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft
Label	Contract Length:
ComboBox		cbxContractLength	Items: Monthly 3 Months 6 Months 12 Months Modifiers: Public
Label	Rent Start Date:
DateTimePicker		dtpRentStartDate	Modifiers: Public
Button	OK	btnOK	DialogResult: OK
Button	Close	btnClose	DialogResult: Cancel
Form			AcceptButton: btnOK CancelButton: btnClose FormBorderStyle: FixedDialog MaximizeBox: False MinimizeBox: False ShowInTaskbar: False

Right-click the RentalAllocation form and click View Code

Import the System.IO and the System.Xml namespaces:

Imports System.IO
Imports System.Xml

Public Class RentalAllocation

End Class

In the Class Name combo box, select txtTenantAcntNbr

In the Method Name combo box, select Leave and implement the event as follows:

Private Sub txtTenantAcntNbr_Leave(ByVal sender As Object, _
                                       ByVal e As System.EventArgs) _
                                       Handles txtTenantAcntNbr.Leave
    Dim Filename As String = "C:\Solas Property Rental\tenants.xml"
    Dim docTenants As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        docTenants.Load(Filename)
        Dim TenantElement As XmlElement = docTenants.DocumentElement
        Dim ListOfTenants As XmlNodeList = TenantElement.ChildNodes
        Dim TenantFound As Boolean = False

        For i = 0 To ListOfTenants.Count - 1
            Dim Node As XmlNode = ListOfTenants(i)

            If Node.FirstChild.InnerText = txtTenantAcntNbr.Text Then
                TenantFound = True
                txtTenantName.Text = Node.FirstChild.NextSibling.InnerText
                txtMaritalStatus.Text = Node.FirstChild.NextSibling.NextSibling.InnerText
            End If
        Next

        If TenantFound = False Then
            MsgBox("There is no tenant with that account number")
            txtTenantAcntNbr.Text = ""
        End If
    Else
        MsgBox("There is no list of tenants to check.")
    End If
End Sub

In the Class Name combo box, select txtPropertyCode

In the Method Name combo box, select Leave and implement the event as follows:

Private Sub txtPropertyCode_Leave(ByVal sender As Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles txtPropertyCode.Leave
    Dim Filename As String = "C:\Solas Property Rental\properties.xml"
    Dim DOMProperties As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        DOMProperties.Load(Filename)
        Dim PropertyElement As XmlElement = DOMProperties.DocumentElement
        Dim ListOfProperties As XmlNodeList = PropertyElement.ChildNodes
        Dim PropertyFound As Boolean = False

        For i = 0 To ListOfProperties.Count - 1
            Dim Node As XmlNode = ListOfProperties(i)

            If Node.FirstChild.InnerText = txtPropertyCode.Text Then
                PropertyFound = True
                txtPropertyType.Text = Node.FirstChild.NextSibling.InnerText
                txtMonthlyRent.Text = Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText
            End If
        Next

        If PropertyFound = False Then
            MsgBox("There is no Property with that code")
            txtPropertyType.Text = ""
        End If
    Else
        MsgBox("There is no list of properties to check.")
    End If
End Sub

To add a new form to the application, in the Solution Explorer, right-click SolasPropertyRental1 -> Add -> Windows Form...
Set the Name to RentalAllocations and press Enter
From the Toolbox, add a ListView to the form

While the new list view is still selected, in the Properties window, click the ellipsis button of the Columns field and create the columns as follows:

(Name)	Text	TextAlign	Width
colAllocationCode	Alloc Code		65
colDateAllocated	Date Allocated	Center	85
colTenantAccount	Tenant #	Center	65
colTenantName	Tenant Name		100
colPropertyCode	Prop Code	Center	65
colPropertyType	Prop Type		75
colContractLength	Contract Length		88
colRentStartDate	Rent Start Date	Center	88
colMonthlyRent	Monthly Rent	Right	76

Design the form as follows:

Solas Property Rental: Rental Allocations

Control	Text	Name	Other Properties
ListView		lvwAllocations	View: Details GridLines: True FullRowSelect: True Anchor: Top, Bottom, Left, Right
Button	New Rental Allocation...	btnNewAllocation	Anchor: Bottom, Right
Button	Close	btnClose

Right-click the Rental Allocations form and click View Code

Import the System.IO and the System.Xml namespaces:

Imports System.IO
Imports System.Xml

Public Class RentalAllocations

End Class

In the Class Name combo box, select txtTenantAcntNbr

In the Method Name combo box, select Leave and implement the event as follows:

Private Sub ShowRentalAllocations()
    Dim Filename As String = "C:\Solas Property Rental\contracts.xml"
    Dim docAllocations As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        lvwAllocations.Items.Clear()

        docAllocations.Load(Filename)
        Dim AllocationElement As XmlElement = docAllocations.DocumentElement
        Dim ListOfAllocations As XmlNodeList = AllocationElement.ChildNodes

        For Each Node As XmlNode In ListOfAllocations
            Dim lviAllocation As ListViewItem = New ListViewItem(Node.FirstChild.InnerText) ' Allocation Code

            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.InnerText) ' Date Allocated
            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.InnerText) ' Tenant Account Number
            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText) ' Tenant Name
            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Property Code
            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Property Type
            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Contract Length
            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Rent Start Date
            lviAllocation.SubItems.Add(Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Monthly Rent
            lvwAllocations.Items.Add(lviAllocation)
        Next
    End If
End Sub

In the Class Name combo box, select (RentalAllocations Events)

In the Method Name combo box, select Load and implement the event as follows:

Private Sub RentalAllocations_Load(ByVal sender As Object, _
                                       ByVal e As System.EventArgs) _
                                       Handles Me.Load
    ShowRentalAllocations()
End Sub

To add a new form to the application, in the Solution Explorer, right-click SolasPropertyRental4 -> Add -> Windows Form...
Set the Name to RentPayment and click Add

Design the form as follows:

Control	Text	Name	Other Properties
Label	Rent Allocation		AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft
Label	Date Received:
DateTimePicker		dtpDateReceived	Format: Short Modifiers: Public
Label	Allocation Code:
MaskedTextBox		txtAllocationCode	Mask: 0000-9999 Modifiers: Public
Label	Receipt #:
TextBox		txtReceiptNumber	Modifiers: Public
Label	Tenant Account #:
TextBox		txtTenantAcntNber	Modifiers: Public
Label	Property Code:
TextBox		txtPropertyCode	Modifiers: Public
Label	Tenant Name:
TextBox		txtTenantName	Modifiers: Public
Label	Property Type:
TextBox		txtPropertyType	Modifiers: Public
Label	Payment Summary		AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft
Label	Month:
Label	Year:
Label	Payment For:
ComboBox		cbxMonths	Modifiers: Public Items: January February March April May June July August September October November December
TextBox		txtYear	Modifiers: Public
Label	Amount Received:
TextBox	0.00	txtAmountReceived	TextAlign: Right Modifiers: Public
Button	OK	btnOK	DialogResult: OK
Button	Close	btnClose	DialogResult: Cancel
Form			AcceptButton: btnOK CancelButton: btnClose FormBorderStyle: FixedDialog MaximizeBox: False MinimizeBox: False ShowInTaskbar: False

Right-click the Rent Payment form and click View Code

Import the System.IO and the System.Xml namespaces:

Imports System.IO
Imports System.Xml

Public Class RentPayment

End Class

In the Class Name combo box, select txtAllocationCode

In the Method Name combo box, select Leave and implement the event as follows:

Private Sub txtAllocationCode_Leave(ByVal sender As Object, _
                                    ByVal e As System.EventArgs) _
                                    Handles txtAllocationCode.Leave
    Dim Filename As String = "C:\Solas Property Rental\contracts.xml"
    Dim docAllocations As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        docAllocations.Load(Filename)
        Dim AllocationElement As XmlElement = docAllocations.DocumentElement
        Dim ListOfAllocations As XmlNodeList = AllocationElement.ChildNodes
        Dim ContractFound As Boolean = False

        For i = 0 To ListOfAllocations.Count - 1
            Dim Node As XmlNode = ListOfAllocations(i)

            If Node.FirstChild.InnerText = txtAllocationCode.Text Then
                ContractFound = True
                txtTenantAcntNber.Text = Node.FirstChild.NextSibling.NextSibling.InnerText
                txtTenantName.Text = Node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText
                txtPropertyCode.Text = Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText
                txtPropertyType.Text = Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText
                txtAmountReceived.Text = Node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText
            End If
        Next

        If ContractFound = False Then
            MsgBox("There is no rental contract with that number")
            txtTenantAcntNber.Text = ""
        End If
    Else
        MsgBox("There is no list of rental contracts to check.")
    End If
End Sub

To add a new form to the application, in the Solution Explorer, right- click SolasPropertyRental4 -> Add -> Windows Form...
Set the Name to RentPayments and press Enter
From the Toolbox, add a ListView to the form

While the new list view is still selected, in the Properties window, click the ellipsis button of the Columns field and create the columns as follows:

(Name)	Text	TextAlign	Width
colReceiptNumber	Receipt #	Right
colDateReceived	Date Received	Center	85
colAllocationCode	Alloc Code	Center	65
colTenantAccount	Tenant #	Center	65
colTenantName	Tenant Name		100
colPropertyCode	Prop Code	Center	65
colPropertyType	Prop Type		75
colPaymentFor	Payment For		88
colAmountReceived	Amount	Right	50

Design the form as follows:

Control	Text	Name	Other Properties
ListView		lvwRentPayments	View: Details GridLines: True FullRowSelect: True Anchor: Top, Bottom, Left, Right
Button	New Rent Payment...	btnNewPayment	Anchor: Bottom, Right
Button	Close	btnClose	Anchor: Bottom, Right

Right-click the Rent Payments form and click View Code

Import the System.IO and the System.Xml namespaces:

Imports System.IO
Imports System.Xml

Public Class RentPayments

End Class

In the Class Name combo box, select txtTenantAcntNbr

In the Method Name combo box, select Leave and implement the event as follows:

Private Sub ShowRentPayments()
    Dim Filename As String = "C:\Solas Property Rental\payments.xml"
    Dim DocumentPayments As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        lvwRentPayments.Items.Clear()

        DocumentPayments.Load(Filename)
        Dim AllocationElement As XmlElement = DocumentPayments.DocumentElement
        Dim ListOfAllocations As XmlNodeList = AllocationElement.ChildNodes

        For Each Node As XmlNode In ListOfAllocations
            Dim lviPayment As ListViewItem = New ListViewItem(node.FirstChild.InnerText) ' Receipt Number

            lviPayment.SubItems.Add(node.FirstChild.NextSibling.InnerText) ' Date Received
            lviPayment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.InnerText) ' Allocation Code
            lviPayment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText) ' Tenant Account Number
            lviPayment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText)  ' Tenant Name
            lviPayment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Property Code
            lviPayment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Property Type
            lviPayment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Payment For
            lviPayment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText) ' Amount
            lvwRentPayments.Items.Add(lviPayment)
        Next
    End If
End Sub

In the Class Name combo box, select (RentPayments.Events)

In the Method Name combo box, select Load and implement the event as follows:

Private Sub RentPayments_Load(ByVal sender As Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles Me.Load
    ShowRentPayments()
End Sub

In the Solution Explorer, right-click Form1.vb and click Rename
Set the name to Central.vb and press Enter twice to display the form

Design the form as follows:

Control	Text	Name
Button	Tenants	btnTenants
Button	Rental Properties	btnRentalProperties
Button	Rental Allocations	btnRentalAllocations
Button	C&lose	btnClose

Right-click the form and click View Code
In the Class Name combo box, select btnRentPayment

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnRentPayments_Click(ByVal sender As Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnRentPayments.Click
    Dim frmPayment As RentPayments = New RentPayments
    frmPayment.Show()
nd Sub

In the Class Name combo box, select btnRentalAllocations

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnRentalAllocations_Click(ByVal sender As Object, _
                                       ByVal e As System.EventArgs) _
                                       Handles btnRentalAllocations.Click
    Dim frmAllocations As RentalAllocations = New RentalAllocations
    frmAllocations.ShowDialog()
End Sub

In the Class Name combo box, select btnTenants

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnTenants_Click(ByVal sender As Object, _
                             ByVal e As System.EventArgs) _
                             Handles btnTenants.Click
    Dim frmTenants As Tenants = New Tenants
    frmTenants.ShowDialog()
End Sub

In the Class Name combo box, select btnRentalProperties

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnRentalProperties_Click(ByVal sender As Object, _
                                      ByVal e As System.EventArgs) _
                                      Handles btnRentalProperties.Click
    Dim frmProperties As RentalProperties = New RentalProperties
    frmProperties.ShowDialog()
End Sub

In the Class Name combo box, select btnClose

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnClose_Click(ByVal sender As Object, _
                           ByVal e As System.EventArgs) _
                           Handles btnClose.Click
    End
End Sub

Save all

Appending an Element

To assist with in programmatically creating a new element, the XmlDocument class provides the CreateElement() method that is overloaded with three versions. One of the versions uses the following syntax:

Public Function CreateElement(name As String) As XmlElement

Using this method, to create a new element, call it and pass it the name of the element. For example, imagine you want to add a new Title element to the above file. You would start with code as follows:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DOMDocument As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        DOMDocument.Load(Filename)

        Dim NewElement As XmlElement = DOMDocument.CreateElement("Title")
    End If
End Sub

In order to add the new element to the file, you must specify its position in the tree: whether it would be the first or the last node, whether you want to position it before or after a node of your choice. For example, if you want to add a new Title element to the above file, it would be considered a child of the root, that is, a child of the XmlDocument.DocumentElement property. In the previous lesson, we learned how to get a reference to the root node.

To support the positions of existing nodes, the XmlNode class, which is the ancestor of all XML nodes of the .NET Framework, provides various appropriate methods. One of these methods is AppendChild(), which is used to add an element as the last child of its parent. The syntax of the XmlNode.AppendChild() method is:

Public Overridable Function AppendChild(newChild As XmlNode) As XmlNode

When calling this method, pass the XmlNode object you had previous created. After adding the node, if you want the file to keep it, you should save it. Here is an example:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
        Dim Filename As String = "videos.xml"
        Dim DOMDocument As XmlDocument = New XmlDocument

        If File.Exists(Filename) Then
            DOMDocument.Load(Filename)

            Dim RootElement As XmlElement = DOMDocument.DocumentElement
            Dim NewElement As XmlElement = DOMDocument.CreateElement("title")
            RootElement.AppendChild(NewElement)

            DOMDocument.Save(Filename)
        End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <title>The Distinguished Gentleman</title>
  <title />
</videos>

Notice that the newly added element is empty.

Adding the Inner Text of an Element

Suppose you have the following videos.xml file:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

Imagine that you want to add a video element. You have a choice of adding one, more than one, or all child elements of the video node. To perform this operation, one solution you can use is to "build" all child elements of the video element, then add the node as a whole.

In the previous lesson, we saw that the XmlNode.InnerXml property comprises a node, its markup, its children and their markup. This means that you can create the child node(s) with its (their) markup(s) as a string and assign that string to an XmlNode.InnerXml string. To do this, you would need the set version of the InnerXml property. It is declared as follows:

Public Overridable Property InnerXml As String

Here is an example that adds a complete new video node to the above XML file:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DOMDocument As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        DOMDocument.Load(Filename)

        Dim Element As XmlElement = DOMDocument.CreateElement("video")
        Dim strNewvideo As String = "<title>Other People's Money</title>" & _
                                    "<director>Alan Brunstein</director>" & _
                                    "<length>114 Minutes</length>" & _
                                    "<format>VHS</format>" & _
                                    "<rating>PG-13</rating>"

        Element.InnerXml = strNewvideo
        DOMDocument.DocumentElement.AppendChild(Element)

        DOMDocument.Save(Filename)
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video>
    <title>Other People's Money</title>
    <director>Alan Brunstein</director>
    <length>114 Minutes</length>
    <format>VHS</format>
    <rating>PG-13</rating>
  </video>
</videos>

Practical Learning: Introducing operations on XML Elements

In the Solution Explorer, right-click Tenants.vb and click View Code
In the Class Name combo box, select btnNewTenant

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnNewTenant_Click(ByVal sender As Object, _
                                   ByVal e As System.EventArgs) _
                                   Handles btnNewTenant.Click
        Dim AccountNumber As String
        Dim FullName As String
        Dim MaritalStatus As String
        Dim PhoneNumber As String

        ' If this directory doesn't exist, create it
        Directory.CreateDirectory("C:\Solas Property Rental")
        ' This is the XML file that holds the list of tenants
        Dim Filename As String = "C:\Solas Property Rental\tenants.xml"
        ' This is the dialog box from where a tenant is created
        Dim editor As TenantEditor = New TenantEditor

        ' Display the Tenant Editor Dialog and find out if the 
        ' user clicked OK after filling its controls
        If editor.ShowDialog() = DialogResult.OK Then
            ' We will need a reference to the XML document
            Dim DOMTenants As XmlDocument = New XmlDocument

            ' Find out if the file exists already
            ' If it doesn't, then create it
            If Not File.Exists(Filename) Then
                DOMTenants.LoadXml("<?xml version=""1.0"" encoding=""utf-8""?>" & _
                                   "<Tenants></Tenants>")
                DOMTenants.Save(Filename)
            End If

            ' At this time, we have a Tenants.xml file. Open it
            DOMTenants.Load(Filename)

            ' Get a reference to the root node
            Dim RootElement As XmlElement = DOMTenants.DocumentElement

            ' Prepare the values of the XML element
            AccountNumber = editor.txtAccountNumber.Text
            FullName = editor.txtFullName.Text
            MaritalStatus = editor.cbxMaritalStatus.Text
            PhoneNumber = editor.txtPhoneNumber.Text

            ' Create an element named Tenant
            Dim TenantElement As XmlElement = DOMTenants.CreateElement("Tenant")
            ' Create the XML code of the child element of Tenant
            Dim strTenant As String = "<AccountNumber>" & AccountNumber & _
                                      "</AccountNumber>" & _
                                      "<FullName>" & FullName & _
                                      "</FullName>" & _
                                      "<MaritalStatus>" & MaritalStatus & _
                                      "</MaritalStatus>" & _
                                      "<PhoneNumber>" & PhoneNumber & _
                                      "</PhoneNumber>"
            TenantElement.InnerXml = strTenant
            ' Append the new element as a child of Tenant
            DOMTenants.DocumentElement.AppendChild(TenantElement)

            ' Save the XML file
            DOMTenants.Save("C:\Solas Property Rental\tenants.xml")
            ' Since the content of the XML file has just been changed,
            ' re-display the list of tenants
            ShowTenants()
        End If
End Sub

In the Class Name combo box, select btnClose

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnClose_Click(ByVal sender As Object, _
                               ByVal e As System.EventArgs) _
                               Handles btnClose.Click
        Close()
End Sub

In the Solution Explorer, right-click RentalProperties.vb and click View Code
In the Class Name combo box, select btnNewProperty

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnNewProperty_Click(ByVal sender As Object, _
                                     ByVal e As System.EventArgs) _
                                     Handles btnNewProperty.Click
        ' If this directory doesn't exist, create it
        Directory.CreateDirectory("C:\Solas Property Rental")
        ' This is the XML file that holds the list of proeprties
        Dim Filename As String = "C:\Solas Property Rental\properties.xml"
        Dim Editor As PropertyEditor = New PropertyEditor

        Dim RandomNumber As Random = New Random
        Editor.txtPropertyCode.Text = RandomNumber.Next(100000, 999999)

        If Editor.ShowDialog() = DialogResult.OK Then
            Dim PropertyCode As String
            Dim PropertyType As String
            Dim Status As String
            Dim Bedrooms As Integer
            Dim Bathrooms As Single
            Dim MonthlyRent As Double

            ' We will need a reference to the XML document
            Dim docProperty As XmlDocument = New XmlDocument

            ' Find out if the file exists already
            ' If it doesn't, then create it
            If Not File.Exists(Filename) Then
                docProperty.LoadXml("<?xml version=""1.0"" encoding=""utf-8""?>" & _
                                    "<Properties></Properties>")
                docProperty.Save(Filename)
            End If

            ' Open the XML file
            docProperty.Load(Filename)

            ' Get a reference to the root node
            Dim RootElement As XmlElement = docProperty.DocumentElement

            PropertyCode = Editor.txtPropertyCode.Text
            PropertyType = Editor.cbxPropertyTypes.Text
            Bedrooms = CInt(Editor.txtBedrooms.Text)
            Bathrooms = CSng(Editor.txtBathrooms.Text)
            MonthlyRent = CDbl(Editor.txtMonthlyRent.Text)
            Status = Editor.cbxStatus.Text

            Dim PropertyElement As XmlElement = docProperty.CreateElement("Property")
            Dim strNewCustomer As String = "<PropertyCode>" & PropertyCode & _
                                    "</PropertyCode>" & "<PropertyType>" & _
                                    PropertyType & "</PropertyType>" & _
                                    "<Bedrooms>" & Bedrooms& "</Bedrooms>" & _
                                    "<Bathrooms>" & FormatNumber(Bathrooms) & _
                                    "</Bathrooms>" & "<MonthlyRent>" & _
                                    FormatNumber(MonthlyRent) & _
                                    "</MonthlyRent>" & _
                                    "<Status>" & Status & "</Status>"

            PropertyElement.InnerXml = strNewCustomer
            docProperty.DocumentElement.AppendChild(PropertyElement)

            docProperty.Save("C:\Solas Property Rental\properties.xml")
            ShowProperties()
        End If
End Sub

In the Class Name combo box, select btnClose

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnClose_Click(ByVal sender As Object, _
                               ByVal e As System.EventArgs) _
                               Handles btnClose.Click
        Close()
End Sub

Execute the application

Use the Tenants button and its New Tenant button to create the following Tenants:

Account #	Full Name	Marital Status	Phone #
20-48-46	Lenny Crandon	Single	(240) 975-9093
57-97-15	Joan Ramey	Married	(301) 304-5845
19-38-84	Peter Sellars	Married	(240) 801-7974
24-68-84	Alberta Sanson	Separated	(202) 917-0095
47-80-95	Urlus Flack	Single	(703) 203-7947

Use the Rental Properties button and its New Property button to create the following properties:

Prop Code	Property Types	Bedrooms	Bathrooms	Monthly Rent	Status
527-992	Apartment	1	1	925	Available
726-454	Apartment	2	1	1150.5	Available
476-473	Single Family	5	3.5	2250.85	Occupied
625-936	Townhouse	3	2.5	1750	Available
179-738	Townhouse	4	2.5	1920.5	Available
727-768	Single Family	4	2.5	2140.5	Needs Repair
371-801	Apartment	3	2	1250.25	Available
241-536	Townhouse	3	1.5	1650.5	Occupied

Close the forms and return to your programming environment

Adding an Element With Value

Consider the following XML file named videos.xml:

<?xml version="1.0" encoding="utf-8" ?>
<videos>
  <title>The Distinguished Gentleman</title>
</videos>

If you want the element to have a value, the XmlDocument class provides the CreateTextNode() method. This method returns an XmlText value. The syntax of this method is:

Public Overridable Function CreateTextNode(text As String) As XmlText

This method takes as argument the string that would constitute the value of the element. Before calling it, you should have used the XmlNode.AppendChild() method to create a node. Calling this method on the LastChild node of the one that called the AppendChild() would specify the value of the new node. Here is an example:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
        Dim Filename As String = "videos.xml"
        Dim DOMDocument As XmlDocument = New XmlDocument

        If File.Exists(Filename) Then
            DOMDocument.Load(Filename)
            Dim RootElement As XmlElement = DOMDocument.DocumentElement

            Dim ElementTitle As XmlElement = DOMDocument.CreateElement("title")
            Dim TextVideo As XmlText = DOMDocument.CreateTextNode("Basic Instinct")

            RootElement.AppendChild(ElementTitle)
            RootElement.LastChild.AppendChild(TextVideo)

            DOMDocument.Save(Filename)
        End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <title>The Distinguished Gentleman</title>
  <title>Basic Instinct</title>
</videos>

The combination of calls to XmlDocument.CreateElement() and XmlDocument.CreateTextNode() allow you to create a new element that has a value.

Consider the following XML file named "videos.xml":

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>The Distinguished Gentleman</title>
  </video>
  <video>
    <title>Basic Instinct</title>
  </video>
</videos>

Notice that the root, videos, has a repetitive child named video. This video child has its own child named Title. Imagine that you want to add a new video node that has a child. To do this, first create an empty video node as a child of the root. We learned earlier how to do that:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
        Dim Filename As String = "videos.xml"
        Dim DOMDocument As XmlDocument = New XmlDocument

        If File.Exists(Filename) Then
            DOMDocument.Load(Filename)

            Dim RootElement As XmlElement = DOMDocument.DocumentElement
            Dim Element As XmlElement = DOMDocument.CreateElement("video")
            RootElement.AppendChild(Element)
        End If
End Sub

After creating the new child of the root, initialize the grand child with the desired name (the name does not have to be one of the existing names) and a value (which is optional if you do not want the new node to have a value). Once the new node is ready, add it as the last child of the root. If this new node has a value, add its XmlText object as the LastChild of the LastChild of the root. Here is an example of how you would do this:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
        Dim Filename As String = "videos.xml"
        Dim DOMDocument As XmlDocument = New XmlDocument

        If File.Exists(Filename) Then
            DOMDocument.Load(Filename)

            Dim RootElement As XmlElement = DOMDocument.DocumentElement
            Dim Element As XmlElement = DOMDocument.CreateElement("video")
            RootElement.AppendChild(Element)

            RootElement = DOMDocument.DocumentElement

            Element = DOMDocument.CreateElement("title")
            Dim TextVideo As XmlText = DOMDocument.CreateTextNode("Her Alibi")

            RootElement.LastChild.AppendChild(Element)
            RootElement.LastChild.LastChild.AppendChild(TextVideo)

            DOMDocument.Save(Filename)
        End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>The Distinguished Gentleman</title>
  </video>
  <video>
    <title>Basic Instinct</title>
  </video>
  <video>
    <title>Her Alibi</title>
  </video>
</videos>

Now consider the following file:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

The root, videos, has a child named video. The video node has many child nodes. By now, we know how to add a child to the root. We also saw how to add a grand child with value to the root. To had many (grand) children to a node, first build the node, add it to the root, then continuously add the necessary nodes, one at a time, including its name and its optional value. This would be done as follows:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              TenamHandles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DOMDocument As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        DOMDocument.Load(Filename)

        Dim RootElement As XmlElement = DOMDocument.DocumentElement
        Dim Element As XmlElement = DOMDocument.CreateElement("video")
        RootElement.AppendChild(Element)

        RootElement = DOMDocument.DocumentElement

        Element = DOMDocument.CreateElement("title")
        Dim TextVideo As XmlText = DOMDocument.CreateTextNode("The Day After Tomorrow")
        RootElement.LastChild.AppendChild(Element)
        RootElement.LastChild.LastChild.AppendChild(TextVideo)

        Element = DOMDocument.CreateElement("director")
        TextVideo = DOMDocument.CreateTextNode("Roland Emmerich")
        RootElement.LastChild.AppendChild(Element)
        RootElement.LastChild.LastChild.AppendChild(TextVideo)

        Element = DOMDocument.CreateElement("length")
        TextVideo = DOMDocument.CreateTextNode("124 Minutes")
        RootElement.LastChild.AppendChild(Element)
        RootElement.LastChild.LastChild.AppendChild(TextVideo)

        Element = DOMDocument.CreateElement("format")
        TextVideo = DOMDocument.CreateTextNode("DVD")
        RootElement.LastChild.AppendChild(Element)
        RootElement.LastChild.LastChild.AppendChild(TextVideo)

        Element = DOMDocument.CreateElement("rating")
        TextVideo = DOMDocument.CreateTextNode("PG-13")
        RootElement.LastChild.AppendChild(Element)
        RootElement.LastChild.LastChild.AppendChild(TextVideo)

        DOMDocument.Save(Filename)
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video>
    <title>The Day After Tomorrow</title>
    <director>Roland Emmerich</director>
    <length>124 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

Using the same approach, you can add children to children of children, and so on.

Practical Learning: Programmatically Adding an Element

In the Solution Explorer, right-click RentalAllocations.vb and click View Code
In the Class Name combo box, select btnNewAllocation

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnNewAllocation_Click(ByVal sender As Object, _
                                       ByVal e As System.EventArgs) _
                                       Handles btnNewAllocation.Click
    Dim AllocationCode As String
    Dim TenantAccountNumber As String
    Dim TenantName As String
    Dim MaritalStatus As String
    Dim PropertyCode As String
    Dim PropertyType As String
    Dim ContractLength As String
    Dim DateAllocated As DateTime
    Dim RentStartDate As Date
    Dim MonthlyRent As Double

    Dim Editor As RentalAllocation = New RentalAllocation
    Directory.CreateDirectory("C:\Solas Property Rental")
    Dim Filename As String = "C:\Solas Property Rental\contracts.xml"

    If Editor.ShowDialog() = DialogResult.OK Then
        Dim DOMAllocation As XmlDocument = New XmlDocument

        If Not File.Exists(Filename) Then
            DOMAllocation.LoadXml( _
		"<?xml version=""1.0"" encoding=""utf-8""?>" & _
                "<Allocations></Allocations>")
            DOMAllocation.Save(Filename)
        End If

        DOMAllocation.Load(Filename)

        Dim RootElement As XmlElement = DOMAllocation.DocumentElement

        AllocationCode = Editor.txtAllocationCode.Text
        DateAllocated = Editor.dtpDateAllocated.Value
        TenantAccountNumber = Editor.txtTenantAcntNbr.Text
        TenantName = Editor.txtTenantName.Text
        MaritalStatus = Editor.txtMaritalStatus.Text
        PropertyCode = Editor.txtPropertyCode.Text
        PropertyType = Editor.txtPropertyType.Text
        MonthlyRent = CDbl(Editor.txtMonthlyRent.Text)
        ContractLength = Editor.cbxContractLengths.Text
        RentStartDate = Editor.dtpRentStartDate.Value

        Dim RootElement As XmlElement = DOMAllocation.DocumentElement
        Dim AllocationElement As XmlElement = _
		DOMAllocation.CreateElement("RentalAllocation")
        RootElement.AppendChild(AllocationElement)

        RootElement = DOMAllocation.DocumentElement

        AllocationElement = DOMAllocation.CreateElement("AllocationCode")
        Dim txtAllocation As XmlText = _
		DOMAllocation.CreateTextNode(AllocationCode)
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("DateAllocated")
        txtAllocation = _
		DOMAllocation.CreateTextNode(DateAllocated.ToString("d"))
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = _
		DOMAllocation.CreateElement("TenantAccountNumber")
        txtAllocation = _
		DOMAllocation.CreateTextNode(TenantAccountNumber)
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("TenantName")
        txtAllocation = DOMAllocation.CreateTextNode(TenantName)
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("MaritalStatus")
        txtAllocation = DOMAllocation.CreateTextNode(MaritalStatus)
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("PropertyCode")
        txtAllocation = DOMAllocation.CreateTextNode(PropertyCode)
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("PropertyType")
        txtAllocation = DOMAllocation.CreateTextNode(PropertyType)
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("ContractLength")
        txtAllocation = DOMAllocation.CreateTextNode(ContractLength)
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("RentStartDate")
        txtAllocation = _
		DOMAllocation.CreateTextNode(RentStartDate.ToString("d"))
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        AllocationElement = DOMAllocation.CreateElement("MonthlyRent")
        txtAllocation = _
		DOMAllocation.CreateTextNode(FormatNumber(MonthlyRent))
        RootElement.LastChild.AppendChild(AllocationElement)
        RootElement.LastChild.LastChild.AppendChild(txtAllocation)

        DOMAllocation.Save(Filename)
        ShowRentalAllocations()
    End If
End Sub

In the Class Name combo box, select btnClose

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnClose_Click(ByVal sender As Object, _
                               ByVal e As System.EventArgs) _
                               Handles btnClose.Click
    Close()
End Sub

In the Solution Explorer, right-click RentPayments.vb and click View Code
In the Class Name combo box, select btnRentPayment

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnNewPayment_Click(ByVal sender As Object, _
                                    ByVal e As System.EventArgs) _
                                    Handles btnNewPayment.Click
        Dim ReceiptNumber As Integer
        Dim AllocationCode As String
        Dim TenantAccountNumber As String
        Dim TenantName As String
        Dim PaymentFor As String
        Dim PropertyCode As String
        Dim PropertyType As String
        Dim DateReceived As DateTime
        Dim AmountReceived As Double

        Dim Editor As RentPayment = New RentPayment
        Dim DOMPayment As XmlDocument = New XmlDocument
        Directory.CreateDirectory("C:\Solas Property Rental")
        Dim Filename As String = "C:\Solas Property Rental\payments.xml"

        ' If some payments were previously made
        If File.Exists(Filename) Then
            ' Open the payments.xml file
            DOMPayment.Load(Filename)

            ' Locate the root element
            Dim AllocationElement As XmlElement = DOMPayment.DocumentElement
            ' Get a list of the child nodes
            Dim ListOfAllocations As XmlNodeList = AllocationElement.ChildNodes

            ' Get the last receipt number
            ReceiptNumber = _
                CInt(ListOfAllocations(ListOfAllocations.Count _
                                        - 1).FirstChild.InnerText) + 1

            Editor.txtReceiptNumber.Text = ReceiptNumber.ToString()
        Else
            ' If no payment has ever been made,
            ' create a new XML file for the payments
            DOMPayment.LoadXml("<?xml version=""1.0"" encoding=""utf-8""?>" & _
                               "<RentPayments></RentPayments>")

            ' We will start the receipt numbers at 101
            ReceiptNumber = 101

            Editor.txtReceiptNumber.Text = ReceiptNumber
        End If

        ' Display the Rent Payment dialog box
        If Editor.ShowDialog() = DialogResult.OK Then
            ' If the user had clicked OK,
            ' Prepare the elements of the XML file
            ReceiptNumber = CInt(Editor.txtReceiptNumber.Text)
            DateReceived = Editor.dtpDateReceived.Value
            AllocationCode = Editor.txtAllocationCode.Text
            TenantAccountNumber = Editor.txtTenantAcntNber.Text
            TenantName = Editor.txtTenantName.Text
            PropertyCode = Editor.txtPropertyCode.Text
            PropertyType = Editor.txtPropertyType.Text
            PaymentFor = Editor.cbxMonths.Text & " " & Editor.txtYear.Text
            AmountReceived = CDbl(Editor.txtAmountReceived.Text)

            ' Get a reference to the root element
            Dim RootElement As XmlElement = DOMPayment.DocumentElement
            ' Create an element named Payment
            Dim PaymentElement As XmlElement = DOMPayment.CreateElement("Payment")
            ' Add the new element as the last node of the root element
            RootElement.AppendChild(PaymentElement)

            ' Get a reference to the root element
            RootElement = DOMPayment.DocumentElement

            ' Create an element
            PaymentElement = DOMPayment.CreateElement("ReceiptNumber")
            ' Create the value of the new element
            Dim TextPayment As XmlText = DOMPayment.CreateTextNode(ReceiptNumber)
            ' Add the new element as a child of the Payment element
            RootElement.LastChild.AppendChild(PaymentElement)
            ' Specify the value of the new element
            RootElement.LastChild.LastChild.AppendChild(TextPayment)

            ' Follow the same logic for the other elements

            PaymentElement = DOMPayment.CreateElement("DateReceived")
            TextPayment = DOMPayment.CreateTextNode(DateReceived.ToString("d"))
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextPayment)

            PaymentElement = DOMPayment.CreateElement("AllocationCode")
            Dim TextAllocation As XmlText = DOMPayment.CreateTextNode(AllocationCode)
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextAllocation)

            PaymentElement = DOMPayment.CreateElement("TenantAccountNumber")
            TextAllocation = DOMPayment.CreateTextNode(TenantAccountNumber)
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextAllocation)

            PaymentElement = DOMPayment.CreateElement("TenantName")
            TextAllocation = DOMPayment.CreateTextNode(TenantName)
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextAllocation)

            PaymentElement = DOMPayment.CreateElement("PropertyCode")
            TextAllocation = DOMPayment.CreateTextNode(PropertyCode)
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextAllocation)

            PaymentElement = DOMPayment.CreateElement("PropertyType")
            TextAllocation = DOMPayment.CreateTextNode(PropertyType)
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextAllocation)

            PaymentElement = DOMPayment.CreateElement("PaymentFor")
            TextAllocation = DOMPayment.CreateTextNode(PaymentFor)
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextAllocation)

            PaymentElement = DOMPayment.CreateElement("AmountReceived")
            TextAllocation = DOMPayment.CreateTextNode(FormatNumber(AmountReceived))
            RootElement.LastChild.AppendChild(PaymentElement)
            RootElement.LastChild.LastChild.AppendChild(TextAllocation)

            DOMPayment.Save(Filename)
            ShowRentPayments()
        End If
End Sub

In the Class Name combo box, select btnClose

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnClose_Click(ByVal sender As Object, _
                               ByVal e As System.EventArgs) _
                               Handles btnClose.Click
    Close()
End Sub

Execute the application

Create the following Rental Allocations:

	Allocation 1	Allocation 2	Allocation 3	Allocation 4
Allocation Code	4205-8274	5920-9417	2792-4075	7957-7294
Date Allocated	8/12/2002	2/18/2004	3/24/2004	10/26/2007
Account #	24-68-84	57-97-15	19-38-84	20-48-46
Prop Code	726-454	625-936	371-801	727-768
Contract Length	12 Months	3 Months	12 Months	6 Months
Start Date	10/1/2002	4/1/2004	6/1/2004	2/1/2008

Create the following Rent Payments:

	Date Received	Allocation Code	Payment For		Amount
	Date Received	Allocation Code	Month	Year	Amount
Payment 1	10/25/2002	4205-8274	October	2002	1150.50
Payment 2	11/28/2002	4205-8274	November	2002	1150.50
Payment 3	4/28/2004	5920-9417	April	2004	1750.00
Payment 4	7/5/2004	2792-4075	June	2004	1250.25
Payment 5	6/3/2004	5920-9417	May	2004	1750.00
Payment 6	7/30/2004	2792-4075	July	2004	1250.25
Payment 7	7/5/2004	5920-9417	June	2004	1750.00
Payment 8	12/30/2002	4205-8274	December	2002	1150.50

Close the DOS window

Exercises

Solas Property Rental

Open the Solas Property Rental database from this lesson
Configure the Rental Allocations form so that, after the user has entered a property code and pressed Tab (or when the control looses focus), the database will first check the status of the property. If the property is occupied, a message box will be displayed to the user and that particular property cannot be selected (the property code text box should be set empty)
Configure the Rent Payments so that the user can decide to see only the payments for one particular tenant (you can create a contextual menu so that if the user right-clicks a certain row and click View Tenant's Payments, the list view would display only that tenant's payments. Of course, make sure the user has a way to display all payments again)


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