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The OnClientDragStart client-side event occurs each time the user begins to drag an item. This event can be cancelled.

The event handler receives two parameters:

  1. The instance of the listbox firing the event

  2. An event arguments parameter containing the following methods:

  • get_sourceItem() - returns the first selected item that is dragged

  • get_sourceItems() -returns an array of the selected items that are dragged

  • set_cancel() - lets you cancel the event and prevent the dragging.

  • get_domEvent() - returns the DOM event object

  • get_htmlElement() - returns the DOM html element which the item is dropped onto.

The following example shows how to cancel the event if the number of the selected/dragged items is greater than 3:

function onClientDragStartHandler(sender, e) {
    if (e.get_sourceItems().length > 3) {
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