OnClientCheckAllChecking

The OnClientCheckAllChecking client-side occurs before the check all items check box is checked. This event is added in 2013 Q3 release (Telerik.Web.UI.dll v.2013.3.1015).

The event handler receives two parameters:

1. The instance of the combobox firing the event.

2. An eventArgs parameter containing the following methods:

• set_cancel lets you prevent the drop-down from opening.

• get_domEvent() returns the DOM event object of the drop-down opening.

• get_checked() returns the value of the Check All check box before it is checked.

The example below shows how to cancel the event if the check all check box is unchecked:

<telerik:RadComboBox RenderMode="Lightweight" ID="RadComboBox1" runat="server" OnClientCheckAllChecking="OnClientCheckAllChecking"
    CheckBoxes="true" EnableCheckAllItemsCheckBox="true">
    <items>
    <telerik:RadComboBoxItem Text="Item1" />
    <telerik:RadComboBoxItem Text="Item2" />
    <telerik:RadComboBoxItem Text="Item3" />
</items>
</telerik:RadComboBox>

function OnClientCheckAllChecking(sender, args) {
    if (args.get_checked()) {
        args.set_cancel(true);
    }
}