AsyncAwaitBestPractices.MVVM

AsyncAwaitBestPractices.MVVM

• Available on NuGet: https://www.nuget.org/packages/AsyncAwaitBestPractices.MVVM/

• Allows for Task to safely be used asynchronously with ICommand:

  • IAsyncCommand : ICommand
  • AsyncCommand : IAsyncCommand
  • IAsyncCommand<T> : ICommand
  • AsyncCommand<T> : IAsyncCommand<T>
  • IAsyncCommand<TExecute, TCanExecute> : IAsyncCommand<TExecute>
  • AsyncCommand<TExecute, TCanExecute> : IAsyncCommand<TExecute, TCanExecute>

• Allows for ValueTask to safely be used asynchronously with ICommand:

  • IAsyncValueCommand : ICommand
  • AsyncValueCommand : IAsyncValueCommand
  • IAsyncValueCommand<T> : ICommand
  • AsyncValueCommand<T> : IAsyncValueCommand<T>
  • IAsyncValueCommand<TExecute, TCanExecute> : IAsyncValueCommand<TExecute>
  • AsyncValueCommand<TExecute, TCanExecute> : IAsyncValueCommand<TExecute, TCanExecute>

• Usage instructions

Setup

• Available on NuGet: https://www.nuget.org/packages/AsyncAwaitBestPractices.MVVM/
• Add to any project supporting .NET Standard 1.0

AsyncCommand

Allows for Task to safely be used asynchronously with ICommand:

• AsyncCommand<TExecute, TCanExecute> : IAsyncCommand<TExecute, TCanExecute>
• IAsyncCommand<TExecute, TCanExecute> : IAsyncCommand<TExecute>
• AsyncCommand<T> : IAsyncCommand<T>
• IAsyncCommand<T> : ICommand
• AsyncCommand : IAsyncCommand
• IAsyncCommand : ICommand

public AsyncCommand(Func<TExecute, Task> execute,
                     Func<TCanExecute, bool>? canExecute = null,
                     Action<Exception>? onException = null,
                     bool continueOnCapturedContext = false)

public AsyncCommand(Func<T, Task> execute,
                     Func<object?, bool>? canExecute = null,
                     Action<Exception>? onException = null,
                     bool continueOnCapturedContext = false)

public AsyncCommand(Func<Task> execute,
                     Func<object?, bool>? canExecute = null,
                     Action<Exception>? onException = null,
                     bool continueOnCapturedContext = false)

public class ExampleClass
{
    bool _isBusy;

    public ExampleClass()
    {
        ExampleAsyncCommand = new AsyncCommand(ExampleAsyncMethod);
        ExampleAsyncIntCommand = new AsyncCommand<int>(ExampleAsyncMethodWithIntParameter);
        ExampleAsyncIntCommandWithCanExecute = new AsyncCommand<int, int>(ExampleAsyncMethodWithIntParameter, CanExecuteInt);
        ExampleAsyncExceptionCommand = new AsyncCommand(ExampleAsyncMethodWithException, onException: ex => Console.WriteLine(ex.ToString()));
        ExampleAsyncCommandWithCanExecuteChanged = new AsyncCommand(ExampleAsyncMethod, _ => !IsBusy);
        ExampleAsyncCommandReturningToTheCallingThread = new AsyncCommand(ExampleAsyncMethod, continueOnCapturedContext: true);
    }

    public IAsyncCommand ExampleAsyncCommand { get; }
    public IAsyncCommand<int> ExampleAsyncIntCommand { get; }
    public IAsyncCommand<int, int> ExampleAsyncIntCommandWithCanExecute { get; }
    public IAsyncCommand ExampleAsyncExceptionCommand { get; }
    public IAsyncCommand ExampleAsyncCommandWithCanExecuteChanged { get; }
    public IAsyncCommand ExampleAsyncCommandReturningToTheCallingThread { get; }
    
    public bool IsBusy
    {
        get => _isBusy;
        set
        {
            if (_isBusy != value)
            {
                _isBusy = value;
                ExampleAsyncCommandWithCanExecuteChanged.RaiseCanExecuteChanged();
            }
        }
    }

    async Task ExampleAsyncMethod()
    {
        await Task.Delay(1000);
    }
  
    async Task ExampleAsyncMethodWithIntParameter(int parameter)
    {
        await Task.Delay(parameter);
    }

    async Task ExampleAsyncMethodWithException()
    {
        await Task.Delay(1000);
        throw new Exception();
    }

    bool CanExecuteInt(int count)
    {
        if(count > 2)
            return true;
        
        return false;
    }

    void ExecuteCommands()
    {
        _isBusy = true;
    
        try
        {
            ExampleAsyncCommand.Execute(null);
            ExampleAsyncIntCommand.Execute(1000);
            ExampleAsyncExceptionCommand.Execute(null);
            ExampleAsyncCommandReturningToTheCallingThread.Execute(null);
            
            if(ExampleAsyncCommandWithCanExecuteChanged.CanExecute(null))
                ExampleAsyncCommandWithCanExecuteChanged.Execute(null);
            
            if(ExampleAsyncIntCommandWithCanExecute.CanExecute(1))
                ExampleAsyncIntCommandWithCanExecute.Execute(1);
        }
        finally
        {
            _isBusy = false;
        }
    }
}

AsyncValueCommand

Allows for ValueTask to safely be used asynchronously with ICommand.

If you're new to ValueTask, check out this great write-up, Understanding the Whys, Whats, and Whens of ValueTask .

• AsyncValueCommand<TExecute, TCanExecute> : IAsyncValueCommand<TExecute, TCanExecute>
• IAsyncValueCommand<TExecute, TCanExecute> : IAsyncValueCommand<TExecute>
• AsyncValueCommand<T> : IAsyncValueCommand<T>
• IAsyncValueCommand<T> : ICommand
• AsyncValueCommand : IAsyncValueCommand
• IAsyncValueCommand : ICommand

public AsyncValueCommand(Func<TExecute, ValueTask> execute,
                            Func<TCanExecute, bool>? canExecute = null,
                            Action<Exception>? onException = null,
                            bool continueOnCapturedContext = false)

public AsyncValueCommand(Func<T, ValueTask> execute,
                            Func<object?, bool>? canExecute = null,
                            Action<Exception>? onException = null,
                            bool continueOnCapturedContext = false)

public AsyncValueCommand(Func<ValueTask> execute,
                            Func<object?, bool>? canExecute = null,
                            Action<Exception>? onException = null,
                            bool continueOnCapturedContext = false)

public class ExampleClass
{
    bool _isBusy;

    public ExampleClass()
    {
        ExampleValueTaskCommand = new AsyncValueCommand(ExampleValueTaskMethod);
        ExampleValueTaskIntCommand = new AsyncValueCommand<int>(ExampleValueTaskMethodWithIntParameter);
        ExampleValueTaskIntCommandWithCanExecute = new AsyncValueCommand<int, int>(ExampleValueTaskMethodWithIntParameter, CanExecuteInt);
        ExampleValueTaskExceptionCommand = new AsyncValueCommand(ExampleValueTaskMethodWithException, onException: ex => Debug.WriteLine(ex.ToString()));
        ExampleValueTaskCommandWithCanExecuteChanged = new AsyncValueCommand(ExampleValueTaskMethod, _ => !IsBusy);
        ExampleValueTaskCommandReturningToTheCallingThread = new AsyncValueCommand(ExampleValueTaskMethod, continueOnCapturedContext: true);
    }

    public IAsyncValueCommand ExampleValueTaskCommand { get; }
    public IAsyncValueCommand<int> ExampleValueTaskIntCommand { get; }
    public IAsyncCommand<int, int> ExampleValueTaskIntCommandWithCanExecute { get; }
    public IAsyncValueCommand ExampleValueTaskExceptionCommand { get; }
    public IAsyncValueCommand ExampleValueTaskCommandWithCanExecuteChanged { get; }
    public IAsyncValueCommand ExampleValueTaskCommandReturningToTheCallingThread { get; }

    public bool IsBusy
    {
        get => _isBusy;
        set
        {
            if (_isBusy != value)
            {
                _isBusy = value;
                ExampleValueTaskCommandWithCanExecuteChanged.RaiseCanExecuteChanged();
            }
        }
    }

    async ValueTask ExampleValueTaskMethod()
    {
        var random = new Random();
        if (random.Next(10) > 9)
            await Task.Delay(1000);
    }

    async ValueTask ExampleValueTaskMethodWithIntParameter(int parameter)
    {
        var random = new Random();
        if (random.Next(10) > 9)
            await Task.Delay(parameter);
    }

    async ValueTask ExampleValueTaskMethodWithException()
    {
        var random = new Random();
        if (random.Next(10) > 9)
            await Task.Delay(1000);

        throw new Exception();
    }

    bool CanExecuteInt(int count)
    {
        if(count > 2)
            return true;
        
        return false;
    }

    void ExecuteCommands()
    {
        _isBusy = true;

        try
        {
            ExampleValueTaskCommand.Execute(null);
            ExampleValueTaskIntCommand.Execute(1000);
            ExampleValueTaskExceptionCommand.Execute(null);
            ExampleValueTaskCommandReturningToTheCallingThread.Execute(null);

            if (ExampleValueTaskCommandWithCanExecuteChanged.CanExecute(null))
                ExampleValueTaskCommandWithCanExecuteChanged.Execute(null);

            if(ExampleValueTaskIntCommandWithCanExecute.CanExecute(2))
                ExampleValueTaskIntCommandWithCanExecute.Execute(2);
        }
        finally
        {
            _isBusy = false;
        }
    }
}