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How to: Set the Selection in List Web Server Controls

  • Artigo

The information in this topic applies to all list Web server controls: ListBox, DropDownList, CheckBoxList, and RadioButtonList.

Normally, users select items in a list Web server control to indicate a choice. However, you might want to preselect items or select items at run time (programmatically) based on some condition.

To set the selection in a list Web server control at design time

  • Set the Selected property of the list item to true. If the control supports multiple selection, you can set Selected property for each item to be selected.

    The following code example shows how to select the first item in a ListBox control.

    <asp:ListBox ID="ListBox1" runat="server">
    <asp:ListItem Selected="True">A</asp:ListItem>
    <asp:ListItem>B</asp:ListItem>
    <asp:ListItem>C</asp:ListItem>
</asp:ListBox>&nbsp;</div>

To set a single selection in a list Web server control programmatically

  • Set the control's SelectedIndex property to the index value of the item to select. The index is zero-based. To set no selection, set SelectedIndex to -1.

    ' Selects the third item.
ListBox1.SelectedIndex = 2

    // Selects the third item.
ListBox1.SelectedIndex = 2;

To set multiple selections in a list control programmatically

  • Loop through the control's Items collection and set the Selected property of every individual item.

    NoteNote

    You can select multiple items only if the control's SelectionMode property is set to Multiple.

    The following code example shows how you can set selections in a multi-selection ListBox control called ListBox1. The code selects every other item.

    Protected Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
   Dim i As Integer
   Dim li As ListItem
   For Each li In ListBox1.Items
      i += 1
      If (i Mod 2 = 0) Then
         li.Selected = True
      End If
   Next
End Sub

    Protected void Button1_Click(object sender, System.EventArgs e)
{
   // Counter.
   int i = 0;
   foreach(ListItem li in ListBox1.Items)
   {
      if( (i%2) == 0)
      {
         li.Selected = true; 
      }
      i += 1;
   }
}

See Also

Reference

CheckBox and CheckBoxList Web Server Controls Overview
DropDownList Web Server Control Overview
ListBox Web Server Control Overview
RadioButton and RadioButtonList Web Server Controls Overview