Why "NotifyCanExecuteChangedFor" didn't fire?

[Phil4121]

Hello!

Currently I'm playing around with the CommunityToolkit for .Net MAUI and DevExpress Controls for .Net MAUI.

In my LoginViewModel I'm using the following code snippets:

I've a class for saving mailadress and password of the user like this:

public partial class LoginModel : ObservableObject
{
    [ObservableProperty]
    private string email;

    [ObservableProperty]
    private string password;
}

In my ViewModel I've got a property of this class which also manage the execution of a command:

[ObservableProperty]
[NotifyCanExecuteChangedFor(nameof(LoginCommand))]
private LoginModel loginCredentials = new();

And now the implementation of the command:

[RelayCommand(CanExecute = nameof(ValiateLoginData))]
private async Task LoginAsync()
{
    try
    {
        IsBusy = true;

        Guard.ArgumentNotNull(LoginCredentials, nameof(LoginCredentials));

        var user = await Auth.AuthenticateUserAsync(LoginCredentials.Email, LoginCredentials.Password);
        await TryUserSignInAsync(user, tryOnlineAuthentication: false);
    }
    finally
    {
        IsBusy = false;
    }
}

ValidateLoginData checks the user input:

private bool ValiateLoginData()
{
    return  !string.IsNullOrEmpty(LoginCredentials.Email) &&
            !string.IsNullOrEmpty(LoginCredentials.Password)
}

Mail and passwort are inserted by user via GUI and are stored in Email and Passwort Property of LoginModel but [NotifyCanExecuteChangedFor] isn't called at all!

Could someone please get me some help?

Thanks
Phil

[pictos]

cc: @Sergio0694

[Sergio0694]

This is by design. [NotifyCanExecuteChangeFor] will notify the command when the annotated property (field) changes. In your case that's not what's happening: you're changing a property inside an object that's assigned to the property. But the value of the property itself is not changing — it's still the same object.

Unrelated: you don't need that IsBusy boilerplate code and additional property within the command, just bind to the IsRunning property of the generated async relay command, that'll do all of that automatically for you 🙂

[Phil4121]

Thank you Sergio for your quick reply!