Change WPF controls from a non-main thread using Dispatcher Invoke

Question

I have recently started programming in WPF and bumped into the following problem  I don t understand how to use the Dispatcher Invoke   method  I have experience in threading and I have made a few simple Windows Forms programs where I just used the  Control CheckForIllegalCrossThreadCalls   false    Yes I know that is pretty lame but these were simple monitoring applications   The fact is now I am making a WPF application which retrieves data in the background  I start off a new thread to make the call to retrieve the data  from a webserver   now I want to display it on my WPF form  The thing is  I cannot set any control from this thread  Not even a label or anything  How can this be resolved   Answer comments   Jalfp   So I use this Dispatcher method in the  new tread  when I get the data  Or should I make a background worker retrieve the data  put it into a field and start a new thread that waits till this field is filled and call the dispatcher to show the retrieved data into the controls

User · Answer

The  japf answer above is working fine and in my case I wanted to change the mouse cursor from a Spinning Wheel back to the normal Arrow once the CEF Browser finished loading the page  In case it can help someone  here is the code   private void Browser LoadingStateChanged object sender  CefSharp LoadingStateChangedEventArgs e       if   e IsLoading             set the cursor back to arrow       Application Current Dispatcher BeginInvoke DispatcherPriority Background           new Action      gt  Mouse OverrideCursor   Cursors Arrow

User · Answer

The first thing is to understand that  the Dispatcher is not designed to run long blocking operation  such as retrieving data from a WebServer      You can use the Dispatcher when you want to run an operation that will be executed on the UI thread  such as updating the value of a progress bar    What you can do is to retrieve your data in a background worker and use the ReportProgress method to propagate changes in the UI thread   If you really need to use the Dispatcher directly  it s pretty simple   Application Current Dispatcher BeginInvoke    DispatcherPriority Background    new Action      gt  this progressBar Value   50

User · Answer

japf has answer it correctly  Just in case if you are looking at multi-line actions  you can write as below   Application Current Dispatcher BeginInvoke    DispatcherPriority Background    new Action      gt         this progressBar Value   50           Information for other users who want to know about performance   If your code NEED to be written for high performance  you can first check if the invoke is required by using CheckAccess flag   if Application Current Dispatcher CheckAccess          this progressBar Value   50    else       Application Current Dispatcher BeginInvoke        DispatcherPriority Background        new Action      gt             this progressBar Value   50                 Note that method CheckAccess   is hidden from Visual Studio 2015 so just write it without expecting intellisense to show it up  Note that CheckAccess has overhead on performance  overhead in few nanoseconds   It s only better when you want to save that microsecond required to perform the  invoke  at any cost  Also  there is always option to create two methods  on with invoke  and other without  when calling method is sure if it s in UI Thread or not  It s only rarest of rare case when you should be looking at this aspect of dispatcher

User · Answer

When a thread is executing and you want to execute the main UI thread which is blocked by current thread  then use the below   current thread   Dispatcher CurrentDispatcher Invoke MethodName      new object     parameter1  parameter2        if passing 2 parameters to method    Main UI thread   Application Current Dispatcher BeginInvoke      DispatcherPriority Background  new Action      gt  MethodName parameter

[c#] Change WPF controls from a non-main thread using Dispatcher.Invoke

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