Check Boxes

Overview of Check Boxes

Introduction

A check box is a control that makes a statement true or false. To perform this validation, the control displays a small square box that the user can click. Here are examples:

To start, the square box may be empty . If the user clicks it, a check mark appears in the square box . If the user clicks a check box that has a check mark in it, the check mark may be removed.

To let the user know what the check box control represents, the control is accompanied by a label that displays the statement. When the square box is empty *, the statement is false. When the square box is filled with a check mark T, the statement is true.

To support check boxes, the .NET Framework provides the CheckBox class. To add a check box to your application at design time, from the Common Controls section of the Toolbox, yon can click the CheckBox control and click the form or a container on the form. Unlike the radio button but like the regular command button, a check box can safely be positioned directly on a form.

To programmatically create a check box, declare a variable of type CheckBox, use the new operator to allocate memory for it, and add it to the Controls collection of its holder. Here is an example:

Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class Starter
        Inherits Form

        Private chkValidate As CheckBox

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

            chkValidate = New CheckBox()

            Controls.Add(chkValidate)

        End Sub

    End Class

    Function Main() As Integer

        Dim frmStart As Starter = New Starter

        Application.Run(frmStart)

        Return 0
    End Function

End Module

Unlike the radio button that usually comes along with other radio buttons, a check box can appear by itself. Even when it comes in a group with others, the behavior of one check box is independent of the other check boxes, even if they belong to the same group.

1. Start a new Windows Application named DaniloPizza1
2. In the Solution Explorer, right-click Form1.vb and click Rename
3. Type Exercise.vb and press Enter
4. On the main menu, click Project -> Add New Item...
5. In the Templates list, click Icon File
6. Set the Name to pizza and click Add
7. Using the Erase tool , wipe its interior to erase its content
8. Use the Ellipse tool and the black color to draw an oval shape
    
   
9. Fill it up with a brown color (the color on the right side of the black)
10. Click the red color
11. Click the Airbrush tool
12. Click the option button and select the Medium brush
     
    
13. Randomly click different parts of the shape
     
    
14. To give the appearance of a crust, use the Pencil tool , click the black color, right-click the brown color, and draw a dark border around the shape
15. With still the black and the brown colors, randomly click and right-click different points in the shape:
     
    
16. Click the white color. Right-click the yellow color. Randomly click and right-click a few times in the shape
17. Click the brown color again and click the Line tool
18. Randomly draw horizontal, vertical, and dialog lines in the shape
     
    
19. Right-click a white section in the drawing area, position the mouse on Current Icon Image Types, and click 16x16, 16 Colors
20. Design it as follows:
     
    
21. Save the icon and close it
22. Use the Icon field of the form in the Properties window to assign the pizza.ico icon to the form
23. Design the form as follows:
     

    Control Text Name Additional Properties GroupBox Pizza Size     RadioButton Small rdoSmall   TextBox 8.95 txtSmall AlignText: Right RadioButton Medium rdoMedium Checked: True TextBox 10.75 txtMedium AlignText: Right RadioButton Large rdoLarge   TextBox 12.95 txtLarge AlignText: Right GroupBox Side Orders     Label Qty     Label Unit Price     Label Sub Total     Label Bread Sticks     TextBox 0 txtQtyBread AlignText: Right TextBox 3.25 txtPriceBread AlignText: Right TextBox 0.00 txtTotalBread AlignText: Right ReadOnly: True Label Buffalo Wings     TextBox 0 txtQtyWings AlignText: Right TextBox 2.15 txtPriceWings AlignText: Right TextBox 0.00 txtTotalWings AlignText: Right ReadOnly: True GroupBox Toppings     CheckBox Pepperoni chkPepperoni   CheckBox Sausage chkSausage   CheckBox Extra Cheese chkExtraCheese   CheckBox Olives chkOlives   CheckBox Onions chkOnions   Label Each Topping     TextBox 0.45 txtEachTopping AlignText: Right GroupBox Drinks     Label Qty     Label Unit Price     Label Sub Total     Label Soda Can     TextBox 0 txtQtyCan AlignText: Right TextBox 1.45 txtPriceCan AlignText: Right TextBox 0.00 txtTotalCan AlignText: Right ReadOnly: True Label Soda 20 Oz.     TextBox 0 txtQtySoda20 AlignText: Right TextBox 1.45 txtPriceSoda20 AlignText: Right TextBox 0.00 txtTotalSoda20 AlignText: Right ReadOnly: True Label Soda 2L Bottle     TextBox 0 txtQtySoda2L AlignText: Right TextBox 1.45 txtPriceSoda2L AlignText: Right TextBox 0.00 txtTotalSoda2L AlignText: Right ReadOnly: True Label Orange Juice     TextBox 0 txtQtyOJ AlignText: Right TextBox 2.25 txtPriceOJ AlignText: Right TextBox 0.00 txtTotalOJ AlignText: Right ReadOnly: True Label Water     TextBox 0 txtQtyWater AlignText: Right TextBox 1.25 txtPriceWater AlignText: Right TextBox 0.00 txtTotalWater AlignText: Right ReadOnly: True Button Close btnClose   Label Total Price     TextBox 0.00 txtTotalPrice AlignRight: Right ReadOnly: True

24. Save everything

By default, a check box appears empty, which makes its statement false. To make the statement true, the user can click it. There are three main ways you can use this property of a check box. To select a check box, you can set its Checked property to True. You can also do it programmatically as follows:

Public Sub InitializeComponent()

            chkValidate = New CheckBox()

            Controls.Add(chkValidate)

            chkValidate.Checked = True

End Sub

To find out if an item is selected, get the value of its Checked property. Another possibility consists of toggling the state of the check mark. For example, you can check or uncheck the check mark when the user clicks another button. To do this, you can simply negate the truthfulness of the control as follows.

Like the radio button, when a check box is clicked, the control fires a CheckedChanged event to let you know that it has been checked. This event is of type EventArgs. If the check box can display only two states, checked or unchecked, this event is enough.

1. Right-click the form and click View Code
2. Inside the class, create the following procedure:
    

   Public Class Exercise Private Sub CalculatePrice() Dim PriceSize As Double Dim PriceEachTopping As Double Dim BWings As Double Dim Bread As Double Dim SodaCan As Double Dim Soda20 As Double Dim Soda2L, OJ As Double Dim Water As Double Dim PriceToppings As Double Dim TotalOrder As Double Dim Pepperoni As Integer Dim Sausage As Integer Dim ExtraCheese As Integer Dim Onions As Integer Dim Olives As Integer Try ' Get the price of pizza depending on the selected size If rdoSmall.Checked = True Then PriceSize = CDbl(txtSmall.Text) End If If rdoMedium.Checked = True Then PriceSize = CDbl(txtMedium.Text) End If If rdoLarge.Checked = True Then PriceSize = CDbl(txtLarge.Text) End If Catch ex As Exception MsgBox("The value you typed for the price of a pizza is invalid" & _ vbCrLf & "Please try again") End Try ' Get the price of a topping if it was selected If chkPepperoni.Checked = True Then Pepperoni = 1 Else Pepperoni = 0 End If If chkSausage.Checked = True Then Sausage = 1 Else Sausage = 0 End If If chkExtraCheese.Checked = True Then ExtraCheese = 1 Else ExtraCheese = 0 End If If chkOnions.Checked = True Then Onions = 1 Else Onions = 0 End If If chkOlives.Checked = True Then Olives = 1 Else Olives = 0 End If ' Get the price of each topping Try PriceEachTopping = CDbl(txtEachTopping.Text) Catch MsgBox("The value you typed for the price of a each topping is invalid" & _ vbCrLf & "Please try again") End Try PriceToppings = (Pepperoni + Sausage + ExtraCheese + _ Onions + Olives) * PriceEachTopping ' Calculate the price of the side dishes ' depending on the quantity entered BWings = CDbl(txtTotalWings.Text) Bread = CDbl(txtTotalBread.Text) ' Calculate the price of the drink(s) SodaCan = CDbl(txtTotalCan.Text) Soda20 = CDbl(txtTotalSoda20.Text) Soda2L = CDbl(txtTotalSoda2L.Text) OJ = CDbl(txtTotalOJ.Text) Water = CDbl(txtTotalWater.Text) TotalOrder = PriceSize + PriceToppings + BWings + Bread + _ SodaCan + Soda20 + Soda2L + OJ + Water txtTotalOrder.Text = FormatNumber(TotalOrder) End Sub End Class

3. Under the above procedure, create the following procedure:
    

   Private Sub rdoSmall_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoSmall.Click, _ rdoMedium.Click, _ rdoMedium.Click, _ chkExtraCheese.Click, _ chkOlives.Click, _ chkOnions.Click, _ chkPepperoni.Click, _ chkSausage.Click CalculatePrice() End Sub

4. Under the above procedure, create the following procedure:
    

   Private Sub ItemPriceLeave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtSmall.Leave, _ txtMedium.Leave, _ txtLarge.Leave, _ txtMedium.Leave, _ txtLarge.Leave, _ txtEachTopping.Leave, _ txtQtyBread.Leave, _ txtPriceBread.Leave, _ txtQtyWings.Leave, _ txtPriceWings.Leave, _ txtQtyCan.Leave, _ txtPriceCan.Leave, _ txtQtySoda20.Leave, _ txtPriceSoda20.Leave, _ txtQtySoda2L.Leave, _ txtPriceSoda2L.Leave, _ txtQtyOJ.Leave, _ txtPriceOJ.Leave, _ txtQtyWater.Leave, _ txtPriceWater.Leave Dim QtyBread As Integer Dim QtyWings As Integer Dim QtyCan As Integer Dim QtySoda20 As Integer Dim QtySoda2L As Integer Dim QtyOJ As Integer Dim QtyWater As Integer Dim PriceBread As Double Dim TotalBread As Double Dim PriceWings As Double Dim TotalWings As Double Dim PriceCan As Double Dim TotalCan As Double Dim PriceSoda20 As Double Dim TotalSoda20 As Double Dim PriceSoda2L As Double Dim TotalSoda2L As Double Dim PriceOJ As Double Dim TotalOJ As Double Dim PriceWater As Double Dim TotalWater As Double ' Retrieve the quantity set in the text box Try QtyBread = CInt(txtQtyBread.Text) Catch ex As Exception MsgBox("The value you entered for the quantify " & _ "of bread sticks is not valid" & _ vbCrLf & "Please try again!") End Try ' Get the unit price of the item Try PriceBread = CDbl(txtPriceBread.Text) Catch ex As Exception MsgBox("The value you entered for the price " & _ "of bread sticks is not valid" & _ vbCrLf & "Please try again!") End Try ' Calculate the sub-total of this item TotalBread = QtyBread * PriceBread ' Display the sub-total in the corresponding text box txtTotalBread.Text = TotalBread.ToString("F") Try PriceWings = CInt(txtQtyWings.Text) Catch ex As Exception MsgBox("The value you entered for the quantify " & _ "of orders of buffalo wings is not valid" & _ vbCrLf & "Please try again!") End Try Try PriceWings = CDbl(txtPriceWings.Text) Catch ex As Exception MsgBox("The value you entered for the price " & _ "of buffalo wings is not valid" & _ vbCrLf & "Please try again!") End Try TotalWings = QtyWings * PriceWings txtTotalWings.Text = TotalWings.ToString("F") Try QtyCan = CInt(txtQtyCan.Text) Catch ex As Exception MsgBox("The value you entered for the " & _ "quantify of soda cans is not valid" & _ vbCrLf & "Please try again!") End Try Try PriceCan = CDbl(txtPriceCan.Text) Catch ex As Exception MsgBox("The value you entered for the " & _ "price of soda cans is not valid" & _ vbCrLf & "Please try again!") End Try TotalCan = QtyCan * PriceCan txtTotalCan.Text = TotalCan.ToString("F") Try QtySoda20 = CInt(txtQtySoda20.Text) Catch ex As Exception MsgBox("The value you entered for the " & _ "quantify of soda 20 Oz. is not valid" & _ vbCrLf & "Please try again!") End Try Try PriceSoda20 = CDbl(txtPriceSoda20.Text) Catch ex As Exception MsgBox("The value you entered for the " & _ "price of soda 20 Oz. is not valid" & _ vbCrLf & "Please try again!") End Try TotalSoda20 = QtySoda20 * PriceSoda20 txtTotalSoda20.Text = TotalSoda20.ToString("F") Try QtySoda2L = CInt(txtQtySoda2L.Text) Catch ex As Exception MsgBox("The value you entered for the quantify " & _ "of bottles of soda 2-litter is not valid" & _ vbCrLf & "Please try again!") End Try Try PriceSoda2L = CDbl(txtPriceSoda2L.Text) Catch ex As Exception MsgBox("The value you entered for the price " & _ "of a bottle of soda is not valid" & _ vbCrLf & "Please try again!") End Try TotalSoda2L = QtySoda2L * PriceSoda2L txtTotalSoda2L.Text = TotalSoda2L.ToString("F") Try QtyOJ = CInt(txtQtyOJ.Text) Catch ex As Exception MsgBox("The value you entered for the quantify " & _ "of a bottle of orange juice is not valid" & _ vbCrLf & "Please try again!") End Try Try PriceOJ = CDbl(txtPriceOJ.Text) Catch ex As Exception MsgBox("The value you entered for the price " & _ "of bottles of orange is not valid" & _ vbCrLf & "Please try again!") End Try TotalOJ = QtyOJ * PriceOJ txtTotalOJ.Text = TotalOJ.ToString("F") Try QtyWater = CInt(txtQtyWater.Text) Catch ex As Exception MsgBox("The value you entered for the quantify " & _ "of bottles of water is not valid" & _ vbCrLf & "Please try again!") End Try Try PriceWater = CDbl(txtPriceWater.Text) Catch ex As Exception MsgBox("The value you entered for the price " & _ "of bottle of water is not valid" & _ vbCrLf & "Please try again!") End Try TotalWater = QtyWater * PriceWater txtTotalWater.Text = TotalWater.ToString("F") CalculatePrice() End Sub

5. In the Class Name combo box, select btnClose
6. 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

7. Execute the application and test the form. Here is an example:
    
   
8. Close the form and return to your programming environment

By default, the square box of a check control is positioned to the left side of its accompanying label. Instead of this default left position, you can change as you wish. The position of the round box with regards to its label is controlled by the CheckAlign property that of type ContentAlignment. To programmatically set the check alignment of a check box, you can call the ContentAlignment enumeration and select the desired value. Here is an example:

Public Sub InitializeComponent()

            chkValidate = New CheckBox()

            Controls.Add(chkValidate)

            chkValidate.CheckAlign = ContentAlignment.MiddleRight

End Sub

Instead of being definitely checked, you can let the user know that the decision of making the statement true or false is not complete. This means that a check box can display as "half-checked". In this case the check mark would appear as if it were disabled. This behavior is controlled through the CheckState property. To provide this functionality, assign the Indeterminate value to its CheckState property. You can do this programmatically as follows:

Public Sub InitializeComponent() chkValidate = New CheckBox() Controls.Add(chkValidate) chkValidate.CheckState = CheckState.Indeterminate End Sub

The CheckState property only allows setting the check box control as "undecided". If you actually want the user to control three states of the control as checked, half-checked, or unchecked, use the ThreeState property.

By setting the CheckState Boolean property to true, the user can click it two to three times to get the desired value. When this ability is given to the user, you can use or check the value of the Indeterminate property to find out whether the control is checked, half-checked, or unchecked.

Here is an example of specifying the check box control as being able to display one of three states:

Public Sub InitializeComponent()

            chkValidate = New CheckBox()

            Controls.Add(chkValidate)

            chkValidate.CheckAlign = ContentAlignment.MiddleRight
            chkValidate.CheckState = CheckState.Indeterminate
            chkValidate.ThreeState = True

End Sub

If a check box is configured to assume one of three states when it's clicked, that is, if the ThreeState property of a check button is set to True, when the user clicks such a button, the button acquires one of the available three states, which are Checked, Unchecked, or Indeterminate. This causes the control to fire a CheckStateChanged event. This event also is of type EventArgs. This means that it does not let you know the current state of the button. You would have to find it out yourself, which is easily done by getting the value of the CheckState property.

By default, a check box appears as a square box that gets a check mark when the user clicks it. Optionally, you can make a check box appear as a toggle button. In that case, the button would appear as a regular button. When the user clicks it, it appears down. If the user clicks it again, it becomes up.

To change the appearance of a check box, assign the Button or Normal value to its Appearance property. The Appearance values are defined in the Appearance enumeration. You can also do this programmatically as follows:

Public Sub InitializeComponent()

            chkValidate = New CheckBox()

            chkValidate.Appearance = Appearance.Button
            Controls.Add(chkValidate)

End Sub

Like the radio button, the check box control fires an AppearanceChanged event when the button's appearance changes from Normal to Button or vice-versa.

1. To start a new application, on the main menu, click File -> New Project...
2. In the Templates list, click Windows Application and set the name to Logic1
3. Click OK
4. Design the form as follows:
    

   Control Text Name Font FlatStyle Appearance Label A   Microsoft Sans Serif, 24pt     Label B   Microsoft Sans Serif, 24pt     Label A ^ B lblOperation Microsoft Sans Serif, 24pt     CheckBox False chkOperand1 Microsoft Sans Serif, 18pt System Button CheckBox False chkOperand2 Microsoft Sans Serif, 18pt System Button CheckBox False chkResult Microsoft Sans Serif, 18pt System Button Button New Operation btnNewOperation Microsoft Sans Serif, 15.75pt     Button Check btnCheckOperation Microsoft Sans Serif, 18pt     Button Close btnClose Microsoft Sans Serif, 15.75pt

5. Double-click the top-left (False) button and implement its event as follows:
    

   Private Sub chkOperand1_CheckedChanged(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles chkOperand1.CheckedChanged If chkOperand1.Checked = True Then chkOperand1.Text = "True" Else chkOperand1.Text = "False" End If End Sub

6. In the Class Name combo box, select chkOperand2
7. In the Method Name combo box, select CheckedChanged and implement its event as follows:
    

   Private Sub chkOperand2_CheckedChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles chkOperand2.CheckedChanged If chkOperand2.Checked = True Then chkOperand2.Text = "True" Else chkOperand2.Text = "False" End If End Sub

8. In the Class Name combo box, select chkResult
9. In the Method Name combo box, select CheckedChanged and implement its event as follows:
    

   Private Sub chkResult_CheckedChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles chkResult.CheckedChanged If chkResult.Checked = True Then chkResult.Text = "True" Else chkResult.Text = "False" End If End Sub

10. In the Class Name combo box, select btnNewOperation
11. In the Method Name combo box, select Click and implement its event as follows:
     

    Private Sub btnNewOperation_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewOperation.Click Dim strBooleanValues As String() = {"True", "False"} Dim strOperations As String() = {"A ^ B", "A V B"} Dim rndNumber As Random = New Random() chkOperand1.Text = strBooleanValues(rndNumber.Next(2)) chkOperand2.Text = strBooleanValues(rndNumber.Next(2)) If chkOperand1.Text = "True" Then chkOperand1.Checked = True Else chkOperand1.Checked = False End If If chkOperand2.Text = "True" Then chkOperand2.Checked = True Else chkOperand2.Checked = False End If lblOperation.Text = strOperations(rndNumber.Next(2)) End Sub

12. In the Class Name combo box, select btnCheckResult
13. In the Method Name combo box, select Click and implement its event as follows:
     

    Private Sub btnCheckResult_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCheckResult.Click ' Logical Conjunction If lblOperation.Text = "A ^ B" Then ' If A = true If chkOperand1.Checked = True Then If chkOperand2.Checked = True Then If chkResult.Checked = True Then ' | A | B | A ^ B | ' | T | T | T | MsgBox("Bravo - Good Answer") ElseIf chkResult.Checked = False Then ' | A | B | A ^ B | ' | T | T | F | MsgBox("Wrong - Get it right next time!") End If ElseIf chkOperand2.Checked = False Then If chkResult.Checked = False Then ' | A | B | A ^ B | ' | T | F | F | MsgBox("Bravo - Good Answer") ElseIf chkResult.Checked = True Then ' | A | B | A ^ B | ' | T | F | T | MsgBox("Wrong - Get it right next time!") End If End If ElseIf chkOperand1.Checked = False Then If chkOperand2.Checked = True Then If chkResult.Checked = False Then ' | A | B | A ^ B | ' | F | T | F | MsgBox("Bravo - Good Answer") ElseIf chkResult.Checked = True Then ' | A | B | A ^ B | ' | F | T | T | MsgBox("Wrong - Get it right next time!") End If ElseIf chkOperand2.Checked = False Then If chkResult.Checked = False Then ' | A | B | A ^ B | ' | F | F | F | MsgBox("Bravo - Good Answer") ElseIf chkResult.Checked = True Then ' | A | B | A ^ B | ' | F | F | T | MsgBox("Wrong - Get it right next time!") End If End If End If End If If lblOperation.Text = "A V B" Then ' Logical Disjunction ' If A = true If chkOperand1.Checked = True Then If chkOperand2.Checked = True Then If chkResult.Checked = True Then ' | A | B | A V B | ' | T | T | T | MsgBox("Bravo - Good Answer") ElseIf chkResult.Checked = False Then ' | A | B | A V B | ' | T | T | F | MsgBox("Wrong - Get it right next time!") End If ElseIf chkOperand2.Checked = False Then If chkResult.Checked = True Then ' | A | B | A V B | ' | T | F | T | MsgBox("Bravo - Good Answer") ElseIf chkResult.Checked = False Then ' | A | B | A V B | ' | T | F | F | MsgBox("Wrong - Get it right next time!") End If End If ElseIf chkOperand1.Checked = False Then If chkOperand2.Checked = True Then If chkResult.Checked = True Then ' | A | B | A V B | ' | F | T | T | MsgBox("Bravo - Good Answer") ElseIf chkResult.Checked = False Then ' | A | B | A V B | ' | F | T | F | MsgBox("Wrong - Get it right next time!") End If ElseIf chkOperand2.Checked = False Then If chkResult.Checked = False Then ' | A | B | A V B | ' | F | F | F | MsgBox("Wrong - Get it right next time!") ElseIf chkResult.Checked = True Then ' | A | B | A V B | ' | F | F | T | MsgBox("Wrong - Get it right next time!") End If End If End If End If End Sub

14. In the Class Name combo box, select btnClose
15. In the Method Name combo box, select Click and implement its event as follows:
     

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

16. Return to the form