CheckAllCheck

The CheckAllCheck event occurs when the check all items check box of the RadComboBox is changed.

The CheckAllCheck event does not fire unless the AutoPostBack property is True .

The CheckAllCheck receives one argument which indicates whether the check all check box is checked or unchecked.

ASPNET

<telerik:RadComboBox RenderMode="Lightweight" ID="RadComboBox1" runat="server" OnCheckAllCheck="RadComboBox1_CheckAllCheck"
	EnableCheckAllItemsCheckBox="true" AutoPostBack="true" CheckBoxes="true">
	<Items>
		<telerik:RadComboBoxItem Text="Item1" />
		<telerik:RadComboBoxItem Text="Item2" />
		<telerik:RadComboBoxItem Text="Item3" />
	</Items>
</telerik:RadComboBox>
<asp:Label ID="Label1" runat="server" />

C#

protected void RadComboBox1_CheckAllCheck(object sender, RadComboBoxCheckAllCheckEventArgs e)
{
	bool allChecked = e.CheckAllChecked;
	if (allChecked)
	{
		Label1.Text = "All items are checked.";
	}
	else
	{
		Label1.Text = "All items are unchecked";
	}
}

VB.NET

Protected Sub RadComboBox1_CheckAllCheck(sender As Object, e As RadComboBoxCheckAllCheckEventArgs)
	Dim allChecked As Boolean = e.CheckAllChecked
	If allChecked Then
		Label1.Text = "All items are checked."
	Else
		Label1.Text = "All items are unchecked"
	End If
End Sub