How can I update progress bar without blocking UI? [duplicate] - multithreading

Question

This question already has answers here:
How do I update the GUI from another thread?
(47 answers)
Closed 1 year ago.
Currently I am creating a background STA thread to keep the UI responsive but it slows down my function calls on the main thread.
Based on this thread How to update progress bar while working in the UI thread I tried the following but the UI only gets updated after all of the work has finished. I tried playing around with the Dispatcher priorities but none of them seem to work.
What I also tried is adding _frmPrg.Refresh() to my Progress callback but this does not seem to change anything.
Dim oProgress = New Progress(Of PrgObject)(Sub(runNumber)
_frmPrg.Invoke((Sub()
_frmPrg.Status = runNumber
End Sub))
End Sub)
System.Windows.Threading.Dispatcher.CurrentDispatcher.BeginInvoke(Sub()
DoLongRunningWork(oProgress, _cancellationToken)
End Sub, System.Windows.Threading.DispatcherPriority.Background)

Answer 1

I can't really help you with your problem, but I'll try to clarify what happens in your posted code.
DoLongRunningWork will be invoked through Dispatcher on the UI thread, when the UI thread is not busy. But once started, it will block the UI thread until it completes. So you can't show a progress this way. Your single chance is, to let DoLongRunningWork run on a background thread. That brings you nothing, if the long-running methods come from office objects, which must be accessed from the UI thread...
The Progress class (see the remarks section) invokes your event handler on the UI thread automatically, so you don't need _frmPrg.Invoke in your event handler.
Maybe you can start a STAthread for your progress form and show it from there. The instance of your Progress class must be created in this thread too, but not before your form is shown to ensure, that the thread becomes a WindowsFormsSynchronisationContext (or you set one explicitly after starting the thread). A plain SynchronisationContext won't work!
At least you get updates in your form this way, but the UI thread of the office app will still be blocked. And of course, any action you make with your progress form must be invoked on the UI thread, if accessing office objects.

Answer 2

After reading some other posts, I decided to suggest another solution. My previous answer still contains usable information, so I'll leave it there. I'm not familiar with VB.NET syntax, so the samples are in C#. I have tested the code in a VSTO plugin for PowerPoint, but it should run in any office application.
Forget the Progress class and background threads. Run everything on the UI thread!
Now use some async code. To stay on the UI thread, we need a "good" SynchronizationContext.
private static void EnsureWinFormsSyncContext()
{
// Ensure that we have a "good" SynchronisationContext
// See https://stackoverflow.com/a/32866156/10318835
if (SynchronizationContext.Current is not WindowsFormsSynchronizationContext)
SynchronizationContext.SetSynchronizationContext(new WindowsFormsSynchronizationContext());
}
This is the event handler of a button. Note the manually added async keyword. The SynchronizationContext.Current gets resetted again and again, so ensure the good one in the EventHandler:
private async void OnButtonClick(object sender, EventArgs e)
{
EnsureWinFormsSyncContext();
// Return from event handler, ensure that we are really async
// See https://stackoverflow.com/a/22645114/10318835
await Task.Yield();
await RunLongOnUIThread();
}
This will be the worker method, also running on the UI thread.
private async Task RunLongOnUIThread()
{
//Dummy code, replace it with your code
var pres = addIn.Application.Presentations.Add();
for (int i = 0; i < 100; i++)
{
Debug.Print("Creating slide {0} on thread {1}", i, Thread.CurrentThread.ManagedThreadId);
// If you have some workloads that can be run on a background
// thread, execute them with await Task.Run(...).
try
{
var layout = pres.Designs[1].SlideMaster.CustomLayouts[1];
var slide = pres.Slides.AddSlide(i + 1, layout);
var shape = slide.Shapes.AddLabel(Microsoft.Office.Core.MsoTextOrientation.msoTextOrientationHorizontal, 0, 15 * i, 100, 15);
shape.TextFrame.TextRange.Text = $"Text on slide {i + 1}";
}
catch (Exception ex)
{
Debug.Print("I don't know what am I doing here, I'm not familiar with PowerPoint... {0}", ex);
}
// Update UI
statusLabel.Text = $"Slide {i + 1} done";
progressBar1.Value = i + 1;
// This is the magic! It gives the main thread the opportunity to update the UI.
// It also processes input messages so you need to disable unwanted buttons etc.
await IdleYield();
}
}
The following method is for Windows Forms Applications where it does the job perfect. I've tried it also in PowerPoint. If you are facing problems, try the WPF flavour with await Dispatcher.Yield(DispatcherPriority.ApplicationIdle) instead of await IdleYield().
private static Task IdleYield()
{
var idleTcs = new TaskCompletionSource<bool>();
void handler(object s, EventArgs e)
{
Application.Idle -= handler;
idleTcs.SetResult(true);
}
Application.Idle += handler;
return idleTcs.Task;
}
Here are the (clickable) links to the answers that I used (I can't put them in the code-blocks...).
Incorrect async/await working, Excel events in Excel Application Level Add-in
When would I use Task.Yield()?
Task.Yield - real usages?
If in your real code something runs not as expected, check the thread you are running on and SynchronizationContext.Current.