How do update a variable periodically ?

[jeromelaban]

From Discord:

I have spent 2 days trying to update a variable cyclically in the UI through binding and I've had no success. I am using the UNO.Extensions template that targets all platforms and includes a 2nd page.

1. View - ViewModel Mapping:

.UseNavigation(ReactiveViewModelMappings.ViewModelMappings, RegisterRoutes)

Where

views.Register(new ViewMap<MainPage, MainViewModel>());

3. ViewModel Inheritance

public partial class MainViewModel : ObservableObject

5. ViewModel Observable Property

[ObservableProperty]
private int _sampleRate;

7. Update Task

public async Task UpdateSampleRateAsync()
    {
        try
        {
            while (true)
            {
                SampleRate = _mcService?.GetSampleRate() ?? -1;
                await Task.Delay(1);
            }
        }
        catch (Exception ex)
        {
            var e = ex;
        }
    }

9. Binding

<TextBlock Text="{Binding SampleRate}" />

or

<TextBlock Text="{x:Bind ViewModel.SampleRate}" />

where:

public sealed partial class MainPage : Page
{
    public MainViewModel? ViewModel => DataContext as MainViewModel;

nothing has worked. and my hot reload also does not work. all i did was create a template with uno command and using latest VS22

[jpgarza93]

I created an "Uno Platform App" project from Visual Studio 22 (v17.3.6) and everything worked as expected:

1. x:Bind
2. Hot Reload

I am just not using the UNO Extensions template:

.UseNavigation(ReactiveViewModelMappings.ViewModelMappings, RegisterRoutes)
views.Register(new ViewMap<MainPage, MainViewModel>());

[francoistanguay]

Can you please try to remove the 1st parameter in UseNavigation? You're using MVVM Toolkit and therefore dont need to rely on Extensions.Reactive

.UseNavigation(ReactiveViewModelMappings.ViewModelMappings, RegisterRoutes)

to

.UseNavigation(RegisterRoutes)

[francoistanguay]

And yes you can add an attachment if my suggestion didnt fix your issue

[jpgarza93]

Removing this ReactiveViewModelMappings.ViewModelMappings did not fix the issue

[jpgarza93]

My bindable property updates correctly one time, but then the next time it tries to assign the value again I get this error:

{"The application called an interface that was marshalled for a different thread. (0x8001010E (RPC_E_WRONG_THREAD))"}

[dr1rrb]

Well this error means that you are trying to update the view from a background thread. Looking at your code, the most probable reason is that you are updating the SampleRate from a background thread, which will raise the NotifyPropertyChanged from that background thread (I think that the MVVM toolkit does not handle multi-threading : it's your responsibility to make sure to go back on the UI thread before updating the SampleRate).

Note: This could be achieve automatically by the system if you make sure to invoke your public async Task UpdateSampleRateAsync() from the UI thread.

You can request for an IDispatcher in your VM constructor do to that.