Xamarin Community Toolkit AsyncValueCommand

Enables the ValueTask type to safely be used asynchronously with an ICommand.

For more information about the ValueTask type, see Understanding the Whys, Whats, and Whens of ValueTask .

Syntax

AsyncValueCommand<TExecute, TCanExecute> : IAsyncValueCommand<TExecute, TCanExecute>

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

AsyncValueCommand<T> : IAsyncValueCommand<T>

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

public AsyncValueCommand(
    Func<T, ValueTask> execute,
    Func<bool> canExecute,
    Action<Exception> onException = null,
    bool continueOnCapturedContext = false,
    bool allowsMultipleExecutions = true)
    : this(execute, _ => canExecute(), onException, continueOnCapturedContext, allowsMultipleExecutions)

AsyncValueCommand : IAsyncValueCommand

public AsyncValueCommand(
    Func<Task> execute,
    Func<object, bool> canExecute = null,
    Action<Exception> onException = null,
    bool continueOnCapturedContext = false,
    bool allowsMultipleExecutions = true)

public AsyncValueCommand(
    Func<Task> execute,
    Func<bool> canExecute,
    Action<Exception> onException = null,
    bool continueOnCapturedContext = false,
    bool allowsMultipleExecutions = true)
    : this(execute, _ => canExecute(), onException, continueOnCapturedContext, allowsMultipleExecutions)

IAsyncValueCommand<TExecute, TCanExecute>

interface IAsyncValueCommand<TExecute, TCanExecute> : IAsyncValueCommand<TExecute>

IAsyncValueCommand<T>

interface IAsyncValueCommand<T> : ICommand

IAsyncValueCommand

interface IAsyncValueCommand : ICommand

Methods

Methods Return Type Description
ExecuteAsync() ValueTask Executes the Command as a ValueTask.
ExecuteAsync(T) ValueTask Executes the Command as a ValueTask.
ExecuteAsync(TExecute) ValueTask Executes the Command as a ValueTask.

Examples

AsyncValueCommand

class MyViewModel
{
    bool _isBusy;

    public MyViewModel()
    {
        ButtonCommand = new AsyncValueCommand(() => ExecuteButtonCommand(), _ => !IsBusy);
    }

    public IAsyncValueCommand ButtonCommand { get; }

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

    async ValueTask ExecuteButtonCommand()
    {
        // ...
    }
}

AsyncValueCommand<T>

class MyViewModel
{
    bool _isBusy;

    public MyViewModel()
    {
        ButtonCommand = new AsyncValueCommand<int>(buttonClicks => ExecuteButtonCommand(buttonClicks), _ => !IsBusy);
    }

    public IAsyncValueCommand<int> ButtonCommand { get; }

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

    async ValueTask ExecuteButtonCommand(int buttonClicks)
    {
        // ...
    }
}

AsyncValueCommand<TExecute, TCanExecute>

class MyViewModel
{
    public MyViewModel()
    {
        ButtonCommand = new AsyncValueCommand<int, bool>(buttonClicks => ExecuteButtonCommand(buttonClicks), isBusy => !isBusy);
    }

    public IAsyncValueCommand<int, bool> ButtonCommand { get; } 
    

    async ValueTask ExecuteButtonCommand(int buttonClicks)
    {
        // ...
    }
}

Sample project

You can see this element in action in the Xamarin community toolkit sample app.

API