Returns the currently active <code>Shell</code>, or null
if no shell belonging to the currently running application
is active.
@return the active shell or null
@exception SWTException <ul>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
<li>ERROR_DEVICE_DISPOSED - if the receiver has been disposed</li>
</ul>
Returns the currently active <code>Shell</code>, or null if no shell belonging to the currently running application is active.
@return the active shell or null
@exception SWTException <ul> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> <li>ERROR_DEVICE_DISPOSED - if the receiver has been disposed</li> </ul>