updating wpf UI while running process

Question

I have a custom WPF control that I want to show when a button is clicked and hide when processing is finished, I am trying this but the control is not visible until the processing is done.

public delegate void UpdateTextCallback(string message);

private void UpdateText(string message)
{
    if (message == "v")
        crclLoading.Visibility = Visibility.Visible;
    else
        crclLoading.Visibility = Visibility.Hidden;
}

private void TestThread()
{
    crclLoading.Dispatcher.Invoke(
        new UpdateTextCallback(this.UpdateText),
        new object[] {"v" }
    );
}

private void TestThread2()
{
    crclLoading.Dispatcher.Invoke(
        new UpdateTextCallback(this.UpdateText),
        new object[] { "s" }
    );
}

and in butoon_click:

Thread show= new Thread(new ThreadStart(TestThread));
show.Start();
//long time conusming processing
Thread hide= new Thread(new ThreadStart(TestThread2));
hide.Start();

mm8 · Accepted Answer · 2017-07-20 12:18:04Z

2

All you do on your background threads is to call Dispatcher.Invoke and this executes the specified delegate synchronously on the UI thread.

Also, you start second thread right after you have started the first one and your code doesn't make much sense at all.

You need to actually perform some potentially long-running operation on the background thread.

By the way, the recommended way to execute something on a background thread is to start a new Task nowadays. Try this:

crclLoading.Visibility = Visibility.Visible;
Task.Factory.StartNew(()=> 
{
    //do something that might take a while here....
    System.Threading.Thread.Sleep(5000);
}).ContinueWith(task => 
{
//and then set the Visibility to Hidden once the task has finished
crclLoading.Visibility = Visibility.Hidden;
}, System.Threading.CancellationToken.None, TaskContinuationOptions.None, TaskScheduler.FromCurrentSynchronizationContext());

answered Jul 20, 2017 at 12:18

mm8

170k10 gold badges70 silver badges102 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Yahya Hussein Over a year ago

by //processing I wanted to say that I have time consuming process here

mm8 Over a year ago

The problem is that you haven't. Check my code. I have a Thread.Sleep that simulates a long-running process. You have no long-running operation in your code.

mm8 Over a year ago

Did you even bother to try my code sample? It will make crclLoading visible for 5 seconds.

Yahya Hussein Over a year ago

of course I am working on it, thank you for your efforts, I will get back to you soon

Yahya Hussein Over a year ago

can I add more explanation to your answer, please? what is the difference between running UI process in background and running computation process in background besides that running UI process on the same thread is more logical?

|

Bradley Uffner · Accepted Answer · 2017-07-20 13:01:25Z

2

In WPF, only the thread that created a DispatcherObject may access that object. For example, a background thread that is spun off from the main UI thread cannot update the contents of a Button that was created on the UI thread. In order for the background thread to access the Content property of the Button, the background thread must delegate the work to the Dispatcher associated with the UI thread. This is accomplished by using either Invoke or BeginInvoke. Invoke is synchronous and BeginInvoke is asynchronous. The operation is added to the event queue of the Dispatcher at the specified DispatcherPriority. Invoke is a synchronous operation; therefore, control will not return to the calling object until after the callback returns.

use Dispatcher.Invoke(new Action(() => MethodName));

edited Jul 20, 2017 at 13:01

Bradley Uffner

17.1k4 gold badges42 silver badges80 bronze badges

answered Jul 20, 2017 at 12:48

Bhushan Shimpi

1001 silver badge10 bronze badges

2 Comments

mm8 Over a year ago

How does this relate to the question...?

mm8 Over a year ago

"but the control is not visible until the processing is done...". That's because all code is being run on the UI thread. Dispatcher.Invoke certainly doesn't change this fact...

Collectives™ on Stack Overflow

updating wpf UI while running process

2 Answers 2

7 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related