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In the previous chapter, we looked at some of the more common user interface elements and how to place and interact with them. The user interfaces presented in Windows Forms are not so different from the familiar MFC ones with which we are familiar. However, the MFC controls can require a lot of programming to make them useful. Some of the Windows Forms elements, such as the TreeView and ListView controls, are very complex and look as if they require a lot of coding to populate and use. This is not always the case, especially when controls are tied to database tables through data binding.

Data Binding Strategies

Data is generally held in tables that have one or more rows and one or more columns. Data Binding is the technique of tying user interface controls directly to individual elements, whole rows, whole columns, or entire tables for the purpose of viewing, manipulating, or editing them.

There are two types of data binding. Simple Binding ties a simple data viewer such as a text box or a numeric edit box to a single data item in a data table. Complex Binding presents a view of a whole table or many tables.

Data Binding Sources

Suitable sources for data binding include any object that exposes the IList interface. Most of the .NET collections implement this interface. Data objects provided by ADO.NET also expose Ilist, and you can also write your own objects that expose data through this interface.

The IList Interface

The Ilist interface has only a few methods. They are as follows:

•Add adds an item to the list.

•Clear removes all items from a list.

•Contains searches a list for a certain value.

•IndexOf determines the index of a particular value within the list.

•Insert places a value into the list before a given index. This moves all following indexes

up one and makes the list longer.

•Remove takes an item out of the list.

•RemoveAt removes one item from a specific index.

Accessing items within the list is done by index. For example, Item x = MyList[n] items are assumed to be objects so any data can be stored in a list if it’s a boxed value type or if it’s a

.NET object.

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Let’s take a look at using the BindingManager and CurrencyManager with a simple application that binds a text box’s Text property to a collection of strings. Listing 3.3.1 shows the DataBound application source code.

LISTING 3.3.1 databound.cs: Simple Binding of Controls to Data

1:namespace Sams

2:{

3:using System;

4:using System.Drawing;

5:using System.Collections;

6:using System.Collections.Specialized;

7:using System.ComponentModel;

8:using System.Windows.Forms;

9:

10:/// <summary>

11:/// Summary description for databound.

12:/// </summary>

13:public class databound : System.Windows.Forms.Form

14:{

15:private Button RightButton;

16:private Button LeftButton;

17:private TextBox textBox2;

18:private TextBox textBox1;

19:private Button DoneButton;

20:

21: private StringCollection sa; 22:

23:public databound()

24:{

25:this.textBox2 = new TextBox();

26:this.RightButton = new Button();

27:this.textBox1 = new TextBox();

28:this.DoneButton = new Button();

29:this.LeftButton = new Button();

30:this.SuspendLayout();

31://

32:// textBox2

33://

34:this.textBox2.Location = new Point(184, 16);

35:this.textBox2.Name = “textBox2”;

36:this.textBox2.TabIndex = 2;

37:this.textBox2.Text = “textBox2”;

38://

39:// RightButton

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LISTING 3.3.1 Continued

84:this.Text = “databound”;

85:this.ResumeLayout(false);

87://This is the setup code for the simple binding example

88://We have bound two text controls to the same StringCollection

90:// This is setting up the “database” (an IList thing)

91:sa=new StringCollection();

92:sa.Add(“Hello databinding”);

93:sa.Add(“Sams publishing”);

94:sa.Add(“C# example”);

95:sa.Add(“By Bob Powell”);

96:

97://This binds the controls to that database.

98:this.textBox1.DataBindings.Add(“Text”,sa,””);

99:this.textBox2.DataBindings.Add(“Text”,sa,””);

100://See the button handlers below for details

101://on how to move through the data.

102:}

103:

104:/// <summary>

105:/// Clean up any resources being used.

106:/// </summary>

107:public override void Dispose()

108:{

109:base.Dispose();

110:}

111:

112:

113://Very simply increments the Position property of the CurrencyManager

114:protected void RightButton_Click (object sender, System.EventArgs e)

115:{

116://Note how updating one position affects all

117://controls bound to this data

118:this.BindingContext[sa].Position++;

119:}

120:

121://Very simply decrements the Position property of the CurrencyManager

122:protected void LeftButton_Click (object sender, System.EventArgs e)

123:{

124://Note how updating one position affects all

125://controls bound to this data

126:this.BindingContext[sa].Position--;

127:}