DialogHost Opened event fires before dialog is rendered - should it be "Opening"?

[BrensNina]

I’m working with MaterialDesignInXaml – DialogHost in a WPF application and I have a question about the behavior (and naming) of the Opened event.

What I’m trying to achieve

I want the dialog to:

1. Appear on screen first

2. Then start loading data asynchronously (showing a loading indicator)

Current behavior

The Opened handler is executed before the dialog is visually rendered.
If I start an async load inside Opened, the dialog appears only after loading finishes

This makes it impossible to reliably show a loading state at dialog startup.

await DialogHost.Show(dialogView, "RootDialog", SalesRecordDialogOpened);

private async void SalesRecordDialogOpened(object sender, DialogOpenedEventArgs eventArgs)
{
    var view = (SalesRecordDialog)eventArgs.Session.Content!;
    var viewModel = (SalesRecordDialogViewModel)view.DataContext;

    await viewModel.LoadSaleRecords();
}

What I tried

• Moving the logic to the UserControl Loaded event

Unfortunately, even with Loaded, the dialog still doesn’t reliably render before the loading starts.

My questions

-Is this behavior by design?

-Would the name Opened be more accurate as Opening, since it fires before the dialog is actually rendered?

-Is there a recommended pattern to ensure:

The dialog is fully visible
Then async loading starts

I’m open to any suggestions to deal with this
Thanks in advance for your help!

[corvinsz]

@BrensNina I can't reproduce the problem you are describing. Could this be a problem with how you are consuming this library?
I have created a repo which showcases your needs:

1. Fully open the dialog
2. Then start loading data asychronously
   https://github.com/user-attachments/assets/9cbbea1e-b20a-4a7b-97af-b2ce7f8b5f20

https://github.com/corvinsz/LoadDataOnDialogHostOpeningExample

LoadDataOnDialogHostOpeningExample is your approach.
LoadDataOnDialogHostOpeningExample2 is my alternative approach described below.

Alternative approach

While your approach works, you are forced to define an async void method, which - as you might know - is not best practice.
I commonly just bind the loaded event of my UserControl (which is the Dialog content) to an async command in my viewmodel.
Here is how:

1. Install the Microsoft.Xaml.Behaviors.Wpf nuget package (this should already be installed if you are using MDIX)
2. Bind the loaded event to an async command in your VM

<i:Interaction.Triggers>
    <i:EventTrigger EventName="Loaded">
        <i:InvokeCommandAction Command="{Binding LoadSaleRecordsCommand}" />
    </i:EventTrigger>
</i:Interaction.Triggers>

3. Leverage the IsRunning property on the generated ICommand to control the visibility of a UI element which indicates loading (e.g. ProgressBar) This assumes you are using the CommunityToolkit.Mvvm library. If not you would just add an IsCommandRunning property to your VM and manage it's state manually.

[BrensNina]

I found my problem, when I call await viewModel.LoadSaleRecords(); (is async Task, i forgot put the Async name convention in final) do things for example load a observable collection after do a query and this blocks UI thread i think unlike Task.Delay that is a "perfect" async implementation. I'm not related in async too deep and idk how to fix this, Do you know of any good async resources get out of this quickly? I'd rather not read all the massive async documentation in mc learn for now. Thanks a lot!

[corvinsz]

If you provide a small POC of what your problem is I might be able to help you out a little easier.
When it comes to resources for learning async/await it really comes down how you learn the best. For example I'm able to learn way faster visually (via images or videos) than by just reading text.

For learning on YouTube you can just search up "c# async await" and find a lot of examples.
Here some recommendations of mine:

• @Keboo: https://www.youtube.com/watch?v=w5bHszEB7Bw
• Raw Coding: https://www.youtube.com/watch?v=il9gl8MH17s
• Coding Tutorials: https://www.youtube.com/@CodingTutorialsAreGo/search?query=async
  The Coding Tutorials channel is one of my favorites. He produces very high quality videos and has done a lot of content on async/await.

[BrensNina]

After spend one day and just for future reference, I'm using EFCore with SQLite, the issue here was the DbSet<>.ToListAsync() method is not working correctly in WPF and all his stuff of UI thread so do you need use Task.Run() to fix this.

https://stackoverflow.com/questions/66341931/ef-core-async-functions-are-blocking-ui