是在Silverlight中调用Dispatcher.CheckAccess（）好的形式吗？

Question

I wonder if the following code buys any performance gains:

if (Deployment.Current.Dispatcher.CheckAccess())
{
    DoUIWork();
}
else
{
    Deployment.Current.Dispatcher.BeginInvoke(() =>
    DoUIWork());
}

Is the Dispatcher smart enough to short circuit a dispatch to the UI thread if its unnecessary?

Answer 1

I couldn't say whether the dispatcher does anything expensive when dispatching from the UI thread to itself, compared with the check. But BeginInvoke from the UI thread may behave differently from executing the operation directly, as it's at least put on the queue rather than invoked immediately. You could tell the difference between this and removing the conditional statement if you had code directly afterwards.

Certainly worth being aware of the control flow, enough to know if the difference doesn't matter.

Answer 2

If it is anything like standard Windows SynchronizationContext (and it probably is) then the two options are not the same. BeginInvoke will basicaly queue up the method to be executed by the dispatcher message pump after the current execution of any existing message has been processed. In your example the two options be the same if you were to use Invoke instead of BeginInvoke.