getActiveWorkbenchWindow() return null 解决办法

/**
* Returns the currently active window for this workbench (if any). Returns
* <code>null</code> if there is no active workbench window. Returns
* <code>null</code> if called from a non-UI thread.
*
* @return the active workbench window, or <code>null</code> if there is
*         no active workbench window or if called from a non-UI thread
*/
public IWorkbenchWindow getActiveWorkbenchWindow();

PlatformUI.getWorkbench().getDisplay().asyncExec(new Runnable() {
public void run() {
IWorkbenchWindow window = PlatformUI.getWorkbench().getActiveWorkbenchWindow();
System.out.println(window);
//做想要做的事情吧。

}
});