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Delegate, Lambda and invoke.

Posted on 2010-11-29
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Last Modified: 2012-05-10
Hi!

I have a question regarding these examples I have here. Is there another way to do this , a better way? Should I use the MethodInvoker?
// using delegate 
this.workflowRuntime.WorkflowCompleted += delegate(object sender, WorkflowCompletedEventArgs e)
{
     BeginInvoke(new MethodInvoker(delegate()
     {
          this.uxInfo.Text = "Completed";
      }));
};

// Using lambda
this.workflowRuntime.WorkflowCompleted += (sender, e) => BeginInvoke(new MethodInvoker(delegate
{
     this.uxInfo.Text = "Completed";
}));

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Question by:AWestEng
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Accepted Solution

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Richard Lee earned 2000 total points
ID: 34231342
Both examples are the same. The second just uses the more concise lamba syntax. Your aim here is to execute the method asynchronously which is achieve by BeginInvoke, however one drawback is that it is executed asynchronously on the same thread that created the UI control's handle was created on, see:

http://msdn.microsoft.com/en-us/library/system.windows.forms.control.begininvoke.aspx

You should consider using the new .NET 4 multi-threading features which will execute on another thread and synchronise to allow UI updates. The following example demonstrates both doing the above in a WPF application, but then customised to work with any type of application.

http://blogs.msdn.com/b/csharpfaq/archive/2010/06/18/parallel-programming-task-schedulers-and-synchronization-context.aspx

DaTribe
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LVL 18

Expert Comment

by:Richard Lee
ID: 34231368
BTW there are four articles in this series. You should probably start from 1 to appreciate fully the new Task Parallel Library (TPL).

http://blogs.msdn.com/b/csharpfaq/archive/2010/06/01/parallel-programming-in-net-framework-4-getting-started.aspx

DaTribe
0
 
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Author Comment

by:AWestEng
ID: 34232412
sounds really nice, I will read the articles, but I use Winforms in this app, is it possible to do it there too?
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LVL 18

Expert Comment

by:Richard Lee
ID: 34232589
The articles focus on WPF and WinForms. The TPL works the same for both the only difference is just how the UI controls are updated.

DaTribe
0
 
LVL 1

Author Comment

by:AWestEng
ID: 34233204
nice reading, thx.

In this case I have a workflow instance, and what I have read the workflow is executed in it's own thread, it is sending back some stuff to the ui tread. But I'm not sure how to use this in my workflow. Is it possible to implement it here to? But when is it good to use, in the case when there is only a lot of data exchange between a backround thread and the UI thread or is good to use  even when there is few data exchange between them?
0
 
LVL 18

Expert Comment

by:Richard Lee
ID: 34233308
When faced with this decision it is prudent to ask yourself if the work to be accomplished will be enough to cause the UI to freeze preventing the user from performing any actions. If the answer is yes, then you have valid candidate.

Besides UI situations if your application required background work to be done (meaning your application can proceed while a background thread does something) then this is a valid candidate.

I think the question to ask here is are you having a problem to begin with or do you just want to perform multi-threading.

What exactly is the problem?

DaTribe
0
 
LVL 1

Author Comment

by:AWestEng
ID: 34233709
in this case  there are really no problems. this is more of a "good practice" question.

I use a "WF - state machine" in my app, and I send back which state is currently executed and show that informaiton in a listview and light up som "leds" that are placed in image that represents the state machine, so I can see how the states are executed.
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LVL 18

Expert Comment

by:Richard Lee
ID: 34237933
If the application is working already and the workflow executes on a separate thread then unless there are more specifics peculiarities then there is no recommended that I can provide besides what has been previously mentioned.

DaTribe
0
 
LVL 1

Author Closing Comment

by:AWestEng
ID: 34238018
thx man :)
0
 
LVL 18

Expert Comment

by:Richard Lee
ID: 34238260
No probs.
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