Tutorial :Using C# MethodInvoker.Invoke() for a GUI app… is this good?



Question:

Using C# 2.0 and the MethodInvoker delegate, I have a GUI application receiving some event from either the GUI thread or from a worker thread.

I use the following pattern for handling the event in the form:

private void SomeEventHandler(object sender, EventArgs e)  {      MethodInvoker method = delegate          {              uiSomeTextBox.Text = "some text";          };        if (InvokeRequired)          BeginInvoke(method);      else          method.Invoke();  }  

By using this pattern I do not duplicate the actual UI code but what I'm not sure about is if this method is good.

In particular, the line

method.Invoke()  

does it use another thread for invoking or does it translate somewhat to a direct call to the method on the GUI thread?


Solution:1

The method.Invoke() call executes the delegate on the current executing thread. Using the BeginInvoke(method) ensures that the delegate is called on the GUI thread.

This is the correct way of avoiding code duplication when the same method can be called both from the GUI thread and other threads.


Solution:2

Personally I like this method:

private void ExecuteSecure(Action a)  {      if (InvokeRequired)          BeginInvoke(a);      else          a();  }  

And then you can write one-liners like this:

ExecuteSecure(() => this.Enabled = true);  


Solution:3

Keep in mind that Control.InvokeRequired returns false if you are on background thread AND Control.IsHandleCreated is false. I would safeguard the code with a Debug.Assert that checks for unmanaged handle creation.


Solution:4

For WinForms, calling Control.Invoke(Delegate) sends a message to the UI's thead's message pump. The thread then processes the message and calls the delegate. Once it has been processed, Invoke stops blocking and the calling thread resumes running your code.


Solution:5

It makes the call on the same thread. You can check by stepping through the code. There is nothing wrong with that approach.


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