C# this.invoke(mydelegate)

Question

I have a program that apparently starts a method referenced by a delegate with the following code: this.Invoke(mydelegate) Can someone refer me to so sort of documentation about this?? Thanks, Keith Stallings

S_Kiryazov · Answer

Sometimes Control.Invoke can save yout life! Exaggerated, of course. But it's quite useful. I'll tell you why. Generally, you implement logic in the form's methods, event handlers etc. But this occasionally causes the UI to freeze when you perform lengthy operations. Psychologists say that even a 30 milisecond delay before the user sees the result of the action he performed (say clicking a button) is noticeable. So you've got to start a worker thread. This task is fairly easy as long as you use ThreadPool.QueueUserWorkItem. But the trouble comes when you need to alter the UI of the form from the worker thread. This can be horrifying the first time you encounter try it. Accessing the controls from the background thread is totally upredictable. In the beggining it seems to be OK but some properties of the controls happen to changed their values, some are empty and throw exceptions that when caught show no StackTrace and you just have no idea what's going on. So, here come the Control.Invoke method. It invokes the delegate in the thread that created the control i.e. the UI thread and gets you rid of a lot of trouble. A neat approach to using it is to implement UI manipulation methods, say ShowProgress, IncrementProgress and HideProgress in this way: delegate void UIManipDelegate( ); private void ShowProgress() { if ( this.InvokeRequired ) { this.Invoke( new UIManipDelegate( ShowProgress ) ); return; } // here do the UI manipulation } In this example the InvokeRequired property shows whether the delegate needs to be invoked in the control's thread i.e. if you are calling IncrementProgress from another thread. This makes the UI manipulation methods universal - you can also call them locally, synchronously in the form without any overhead. If you need to supply parameters to the method you do as follows: public delegate void Incrementer( Int32 value ); public void IncrementProgress( Int32 value ) { if ( progressBar.InvokeRequired ) { progressBar.Invoke( new Incrementer(value), new Object[]{value} ); return; } // here do the UI manipulation }

kstallings · Answer

I found that this is a method provided by .net controls. It is used to invoke a delegate like I deducted, that is just about all there is to it. Keith