Updating UI from events using asyc await

Question

I am trying to understand how to update a UI from an event while using async/await pattern. Below is the test code I am using on a WinForm app. I am not even sure this is the right way to go about it. What is necessary to allow the pwe_StatusUpdate method to update the UI? The cross-thread operation error is thrown there.

Thanks for reading.

 // calling code     ProcessWithEvents pwe = new ProcessWithEvents();     pwe.StatusUpdate += pwe_StatusUpdate;     await pwe.Run();     void pwe_StatusUpdate(string updateMsg)     {       // Error Here: Cross-thread operation not valid: Control '_listBox_Output' accessed from a thread other than the thread it was created on.       _listBox_Output.Items.Add(updateMsg);     } 

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// Class with long running process and event     public delegate void StatusUpdateHandler(string updateMsg);   public class ProcessWithEvents   {     public event StatusUpdateHandler StatusUpdate;      public async Task Run()     {         await Task.Run(() =>         {             for (int i = 0; i < 10; i++)                 {                      RaiseUpdateEvent(String.Format("Update {0}", i));                      Thread.Sleep(500);                 }             });          }          private void RaiseUpdateEvent(string msg)         {         if (StatusUpdate != null)             StatusUpdate(msg);         }    } 

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Answer 1

The async pattern has support for progress updates.

In short, your async method can take an IProgress<T>, and your calling code passes in an implementation of that interface (usually Progress<T>).

public class ProcessWithUpdates {   public async Task Run(IProgress<string> progress)   {     await Task.Run(() =>     {       for (int i = 0; i < 10; i++)       {         if (progress != null)           progress.Report(String.Format("Update {0}", i));         Thread.Sleep(500);       }     });   } }  // calling code ProcessWithUpdates pwp = new ProcessWithUpdates(); await pwp.Run(new Progress<string>(pwp_StatusUpdate));