Lesson 1: Creating and Configuring List-Display Controls in .NET

Encoding QR Code ISO/IEC18004 in .NET Lesson 1: Creating and Configuring List-Display Controls

' VB ListBox1.Items.Insert(2, "This item will be third") // C# listBox1.Items.Insert(2, "This item will be third");

You can use the Items.Remove method to remove an item from the list. This method requires a reference to the object that you want to remove from the items collection. Note that if your control contains a collection of objects that are not strings, you will need to pass a reference to the object itself to remove it, not just to the string represen tation that appears in the control. The following example demonstrates the Items.Remove method.

' VB ListBox1.Items.Remove("This string will be removed") // C# listbox1.Items.Remove("This string will be removed");

If you do not know the actual item that you want to remove at run time but have the index of the item you want to remove, you can use the Items.RemoveAt method. This method removes the item at a given index and adjusts the indexes of the other items accordingly. The Items.RemoveAt method is demonstrated in the following code example:

' VB ' Removes the third item in the list ListBox1.Items.RemoveAt(2) // C# // Removes the third item in the list listBox1.Items.RemoveAt(2);

To remove all items from a list-based control, you can use the Items.Clear method, as shown here:

' VB ListBox1.Items.Clear() // C# listBox1.Items.Clear();

If you want to determine where an item appears in a list programmatically, you can do so by using the Items.IndexOf method. This method takes the item you want to find as an argument and returns an integer that represents the index of that item. If the item

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is not found in the Items collection, the IndexOf method returns -1. An example of the IndexOf method is shown here:

anIndex = ListBox1.IndexOf("A String")

// C# int anIndex;

anIndex = listBox1.IndexOf("A String");

You can also programmatically determine the index of an item that has been selected by the user by using the SelectedIndex property. The SelectedIndex property returns the item that has been selected in the user interface at run time. If more than one item has been selected, the SelectedIndex property can return any of the selected items. The SelectedIndex property is demonstrated here:

// C# int anIndex;

anIndex = listBox1.SelectedIndex;

In controls where the SelectionMode property is set to MultiSimple or MultiExtended, you can return all of the selected indexes by using the SelectedIndices property, as shown in the following example:

Console.WriteLine(ListBox1.Items(i).ToString)

// C# foreach (int i in listBox1.SelectedIndices)

Console.WriteLine(listBox1.Items[i].ToString());

You will frequently want to expose data to the user in list-based controls. You can bind ListBox controls and ComboBox controls (but not CheckedListBox controls) to a data source by using the DataSource, DisplayMember, and ValueMember properties to bind a list-based control to a column of data in a data table.

Add a data source to your project. Adding data sources to your project is covered in detail in 5, Configuring Connections and Connecting to Data.

1. In the Designer, select the list-based control that you want to bind to a data source. 2. In the Properties window, click the DataSource property to open the data source configuration interface, as shown in Figure 3-2. Set the DataSource property to a table contained in one of the data sources in your project.

Figure 3-2

3. In the Properties window, click the DisplayMember property. Visual Studio dis plays the columns in the selected table. This is the column whose rows will be displayed in the control. 4. In the Properties window, click the ValueMember property. Choose a column name in the interface to bind the control to. This is the column whose members will provide the value that is returned from the selected index in the control. The DataSource property indicates the data source (usually a data table) that the data in the control is drawn from. The DisplayMember property represents the column of data in the data source that is displayed to the user in the control. The ValueMember property allows you to designate an additional column of values to be represented in the control. For example, you might set the DisplayMember property to the Products column to indicate a list of products to the user but set the ValueMember to a ProductsCode column that returned a numeric code for each product. In this instance, when ever an item was selected, the SelectedItem property would return the item displayed