Does RaiseCanExecuteChanged need to be called on the UI thread?

[CodingOctocat]

I found this question at StackOverflow, should the RaiseCanExecuteChanged method be executed on the UI thread instead?

Why people use CommandManager.InvalidateRequerySuggested() on ICommands? - StackOverflow

public void RaiseCanExecuteChanged()
{
    Application.Current.Dispatcher.Invoke(() => CanExecuteChanged?.Invoke(this, null)); 
}

[brminnick]

Hi @CodingOctocat!

The answer is "It Depends".

Non UI Frameworks

No, you do not need to marshall RaiseCanExecuteChanged to the main thread

UI Frameworks

If you are using a UI dependent framework, such as WinForms, WPF, Xamarin, etc.,

AND

ICommand is bound to a UI control (eg a Button), then yes you will need to invoke RaiseCanExecuteChanged on the main thread:

Xamarin Example

public IAsyncCommand ButtonCommand { get; } = new AsyncCommand(ExecuteButtonCommand);

static async Task ExecuteButtonCommand()
{
    // Handle Button Command
}

void OnCanExecuteChanged() => Device.BeginInvokeOnMainThread(ButtonCommand.RaiseCanExecuteChanged);

[CodingOctocat]

Thank you! I read the source code, so the default implementation of AABP has no platform detection and it works for non-UI projects? If my project is wpf, I need to compile a copy myself?

[brminnick]

You don't need to compile a copy of AsyncAwaitBestPractices; using the NuGet package works just fine.

On WPF, just make sure to use Application.Current.Dispatcher.Invoke when you call RaiseCanExecuteChanged.

WPF Example

public IAsyncCommand ButtonCommand { get; } = new AsyncCommand(ExecuteButtonCommand);

static async Task ExecuteButtonCommand()
{
    // Handle Button Command
}

void OnCanExecuteChanged() => Application.Current.Dispatcher.Invoke(ButtonCommand.RaiseCanExecuteChanged);

[CodingOctocat]

If I'm lazy and I don't want to manually call RaiseCanExecuteChanged to refresh the UI state every time/every command, and I want the RaiseCanExecuteChanged method to be executed automatically after Execute, then maybe I need to change the source code? (although I don't actually need to, just curious)

[brminnick]

Correct, AsyncAwaitBestPractices will not automatically call RaiseCanExecuteChanged

[CodingOctocat]

Thanks a lot really, I think I understand that part now!