Returns the application defined widget data associated
with the receiver, or null if it has not been set. The
<em>widget data</em> is a single, unnamed field that is
stored with every widget.
<p>
Applications may put arbitrary objects in this field. If
the object stored in the widget data needs to be notified
when the widget is disposed of, it is the application's
responsibility to hook the Dispose event on the widget and
do so.
</p>
@return the widget data
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - when the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - when called from the wrong thread</li>
</ul>
Returns the application defined widget data associated with the receiver, or null if it has not been set. The <em>widget data</em> is a single, unnamed field that is stored with every widget. <p> Applications may put arbitrary objects in this field. If the object stored in the widget data needs to be notified when the widget is disposed of, it is the application's responsibility to hook the Dispose event on the widget and do so. </p>
@return the widget data
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - when the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - when called from the wrong thread</li> </ul>
@see #setData(Object)