Xamarin Forms MvvmCross binding a button command error

Question

I'm working on a Xamarin Forms MvvmCross project. I'm binding a common button command on the view with a IMvxAsyncCommand on the view model, as follows:

• View

   <views:MvxContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                     xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                     xmlns:views="clr- namespace:MvvmCross.Forms.Views;assembly=MvvmCross.Forms"
                     x:Class="TestProject.Pages.TestPage">
   <ContentView>
       <StackLayout>
           <Button Text="Test the command!" Command="{Binding TestAsyncCommand}"/>
       </StackLayout>
   </ContentView>
  

  </views:MvxContentPage>

• View model

   namespace TestProject.ViewModels
   {
       public class TestViewModel : MvxNavigationViewModel
       {
           public TestViewModel(IMvxLogProvider logProvider, IMvxNavigationService navigationService)
               : base(logProvider, navigation)
           {
           }
  
           public IMvxAsyncCommand TestAsyncCommand => new MvxAsyncCommand(async () => await TestAsyncCommandMethod());
  
           private async Task TestAsyncCommandMethod()
           {
               //await some stuff
           }
       }
   }
  

Anythings seems to work fine but rarely sometimes after a pression of the button it becames disable. What could happen? It does not happen if I use Command in place of MvxAsyncCommand, like here:

public Command TestAsyncCommand => new Command(async () => await TestAsyncCommandMethod());

Note: TestAsyncCommandMethod is entirely encased in a try-catch block to avoid possible exceptions.

Answer 1

I think what you are doing wrong here is that instead of creating a Property to Bind the View and the ViewModel you are using a field can you try this:

public IMvxAsyncCommand TestAsyncCommand {get; set;}

And then in your constructor do this:

public TestViewModel(IMvxLogProvider logProvider, IMvxNavigationService navigationService)
        : base(logProvider, navigation)
    {
      TestAsyncCommand = new MvxAsyncCommand(async () => await TestAsyncCommandMethod());
    }

UPDATE

This seems to be a bug with MvvmCross! Issue can be found in the added link

https://github.com/MvvmCross/MvvmCross/issues/1589