Bug 30655 [DND] Check selection in NavigatorDragAdapter.dragStart
bundles/org.eclipse.ui.views/src/org/eclipse/ui/views/navigator/NavigatorDragAdapter.java
return;
		
		if (actualLength < length) {
			String[] tempFileNames = fileNames;
			fileNames = new String[actualLength];
			for (int i = 0; i < actualLength; i++)
				fileNames[i] = tempFileNames[i];
		}
		event.data = fileNames;
	}
	/**
	 * @see DragSourceListener#dragStart
	 */
	public void dragStart(DragSourceEvent event) {
		
		DragSource dragSource = (DragSource) event.widget;
		Control control = dragSource.getControl();
		if (control != control.getDisplay().getFocusControl()) {
			event.doit = false;
			return;
		}
		IStructuredSelection selection =
			(IStructuredSelection) selectionProvider.getSelection();
		for (Iterator i = selection.iterator(); i.hasNext();) {
			Object next = i.next();
			if (!(next instanceof IFile || next instanceof IFolder)) {
				event.doit = false;
				return;
			}
		}