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:

using System;
using System.Drawing;
using System.Windows.Forms;

public class Exercise : System.Windows.Forms.Form
{
    CheckBox chkValidate;

    public Exercise()
    {
        InitializeComponent();
    }

    private void InitializeComponent()
    {
        chkValidate = new CheckBox();

        Controls.Add(chkValidate);
    }
}

public class Program
{
    static int Main()
    {
        System.Windows.Forms.Application.Run(new Exercise());
        return 0;
    }
}

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.cs and click Rename
3. Type Exercise.cs 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:

private void Form1_Load(object sender, System.EventArgs e)
{
        checkBox1.Checked = true;
}

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:

checkBox1.Checked = ! checkBox1.Checked;

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. On the form click the Small radio button
2. Press and hold Shift
3. Click the Medium radio button, the Large radio button, the Pepperoni, the Sausage, the Extra Cheese, the Olives, and the Onions check boxes
4. Release Shift
5. In the Properties window, click the Events button
6. In the Events section, double-click Click
7. Return to the form
8. Click the txtSmall text box
9. Press and hold Shift
10. Click each of the following controls: txtMedium, txtLarge, txtEachTopping, txtQtyBread, txtPriceBread, txtQtyWings, txtPriceWince, txtQtyCan, txtPriceCan, txtQtySoda20, txtPriceSoda20, txtQtySoda2L, txtPriceSoda2L, txtQtyOJ, txtPriceOJ, txtQtyWater, and txtPriceWater
11. Release Shift
12. In the Events section of the Properties window, double-click Leave
13. In the Code Editor, define a method named CalculatePrice() and implement the events as follows:
     

    using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace DaniloPizza1 { public partial class Exercise : Form { public Exercise() { InitializeComponent(); } internal void CalculatePrice() { double PriceSize = 0.00; double PriceEachTopping = 0.00, BWings, Bread, SodaCan, Soda20, Soda2L, OJ, Water, PriceToppings, TotalOrder; int Pepperoni, Sausage, ExtraCheese, Onions, Olives; try { // Get the price of pizza depending on the selected size if (rdoSmall.Checked == true) PriceSize = double.Parse(txtSmall.Text); if (rdoMedium.Checked == true) PriceSize = double.Parse(txtMedium.Text); if (rdoLarge.Checked == true) PriceSize = double.Parse(txtLarge.Text); } catch (FormatException) { MessageBox.Show("The value you typed for the " + "price of a pizza is invalid" + "\nPlease try again"); } // Get the price of a topping if it was selected if (chkPepperoni.Checked == true) Pepperoni = 1; else Pepperoni = 0; if (chkSausage.Checked == true) Sausage = 1; else Sausage = 0; if (chkExtraCheese.Checked == true) ExtraCheese = 1; else ExtraCheese = 0; if (chkOnions.Checked == true) Onions = 1; else Onions = 0; if (chkOlives.Checked == true) Olives = 1; else Olives = 0; // Get the price of each topping try { PriceEachTopping = double.Parse(txtEachTopping.Text); } catch (FormatException) { MessageBox.Show("The value you typed for the price " + "of a each topping is invalid" + "\nPlease try again"); } PriceToppings = (Pepperoni + Sausage + ExtraCheese + Onions + Olives) * PriceEachTopping; // Calculate the price of the side dishes // depending on the quantity entered BWings = double.Parse(txtTotalWings.Text); Bread = double.Parse(txtTotalBread.Text); // Calculate the price of the drink(s) SodaCan = double.Parse(txtTotalCan.Text); Soda20 = double.Parse(txtTotalSoda20.Text); Soda2L = double.Parse(txtTotalSoda2L.Text); OJ = double.Parse(txtTotalOJ.Text); Water = double.Parse(txtTotalWater.Text); TotalOrder = PriceSize + PriceToppings + BWings + Bread + SodaCan + Soda20 + Soda2L + OJ + Water; txtTotalOrder.Text = TotalOrder.ToString("F"); } private void rdoSmall_Click(object sender, EventArgs e) { CalculatePrice(); } private void txtSmall_Leave(object sender, EventArgs e) { int QtyBread = 0, QtyWings = 0, QtyCan = 0, QtySoda20 = 0, QtySoda2L = 0, QtyOJ = 0, QtyWater = 0; double PriceBread = 0.00, TotalBread = 0.00, PriceWings = 0.00, TotalWings = 0.00, PriceCan = 0.00, TotalCan = 0.00, PriceSoda20 = 0.00, TotalSoda20 = 0.00, PriceSoda2L = 0.00, TotalSoda2L = 0.00, PriceOJ = 0.00, TotalOJ = 0.00, PriceWater = 0.00, TotalWater = 0.00; // Retrieve the quantity set in the text box try { QtyBread = int.Parse(txtQtyBread.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of bread sticks is not valid" + "\nPlease try again!"); } // Get the unit price of the item try { PriceBread = double.Parse(txtPriceBread.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price " + "of bread sticks is not valid" + "\nPlease try again!"); } // 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 = int.Parse(txtQtyWings.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify of " + "orders of buffalo wings is not valid" + "\nPlease try again!"); } try { PriceWings = double.Parse(txtPriceWings.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price " + "of buffalo wings is not valid" + "\nPlease try again!"); } TotalWings = QtyWings * PriceWings; txtTotalWings.Text = TotalWings.ToString("F"); try { QtyCan = int.Parse(txtQtyCan.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of soda cans is not valid" + "\nPlease try again!"); } try { PriceCan = double.Parse(txtPriceCan.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price " + "of soda cans is not valid" + "\nPlease try again!"); } TotalCan = QtyCan * PriceCan; txtTotalCan.Text = TotalCan.ToString("F"); try { QtySoda20 = int.Parse(txtQtySoda20.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of soda 20 Oz. is not valid" + "\nPlease try again!"); } try { PriceSoda20 = double.Parse(txtPriceSoda20.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price " + "of soda 20 Oz. is not valid" + "\nPlease try again!"); } TotalSoda20 = QtySoda20 * PriceSoda20; txtTotalSoda20.Text = TotalSoda20.ToString("F"); try { QtySoda2L = int.Parse(txtQtySoda2L.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify of " + "bottles of soda 2-litter is not valid" + "\nPlease try again!"); } try { PriceSoda2L = double.Parse(txtPriceSoda2L.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price " + "of a bottle of soda is not valid" + "\nPlease try again!"); } TotalSoda2L = QtySoda2L * PriceSoda2L; txtTotalSoda2L.Text = TotalSoda2L.ToString("F"); try { QtyOJ = int.Parse(txtQtyOJ.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify of " + "a bottle of orange juice is not valid" + "\nPlease try again!"); } try { PriceOJ = double.Parse(txtPriceOJ.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price of " + "bottles of orange is not valid" + "\nPlease try again!"); } TotalOJ = QtyOJ * PriceOJ; txtTotalOJ.Text = TotalOJ.ToString("F"); try { QtyWater = int.Parse(txtQtyWater.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the quantify " + "of bottles of water is not valid" + "\nPlease try again!"); } try { PriceWater = double.Parse(txtPriceWater.Text); } catch (FormatException) { MessageBox.Show("The value you entered for the price " + "of bottle of water is not valid" + "\nPlease try again!"); } TotalWater = QtyWater * PriceWater; txtTotalWater.Text = TotalWater.ToString("F"); CalculatePrice(); } private void btnClose_Click(object sender, EventArgs e) { Close(); } } }

14. Return to the and double-click the Close button
15. Implement its Click event as follows:
     

    private void btnClose_Click(object sender, System.EventArgs e) { Close(); }

16. Execute the application and test the form. Here is an example:
     
    
17. 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:

private void Form1_Load(object sender, System.EventArgs e)
{
	this.checkBox1.Checked = true;
	this.checkBox1.CheckAlign = ContentAlignment.MiddleRight;
}

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:

this.ccheckBox1.CheckState = checkState.Indeterminate;

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:

private void Form1_Load(object sender, System.EventArgs e)
{
	checkBox1.Checked = true;
	checkBox1.ThreeState = true;
}

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:

private void Form1_Load(object sender, System.EventArgs e)
{
	checkBox1.Checked = true;
	checkBox1.ThreeState = true;
	checkBox1.Appearance = Appearance.Button;
}

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.