Xamarin Community Toolkit AsyncCommand

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

Syntax

AsyncCommand<TExecute, TCanExecute> : IAsyncCommand<TExecute, TCanExecute>

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

AsyncCommand<T> : IAsyncCommand<T>

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

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

AsyncCommand : IAsyncCommand

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

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

IAsyncCommand<TExecute, TCanExecute>

interface IAsyncCommand<TExecute, TCanExecute> : IAsyncCommand<TExecute>

IAsyncCommand<T>

interface IAsyncCommand<T> : ICommand

IAsyncCommand

interface IAsyncCommand : ICommand

Methods

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

Examples

AsyncCommand

class MyViewModel
{
    bool _isBusy;

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

    public IAsyncCommand ButtonCommand { get; }

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

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

AsyncCommand<T>

class MyViewModel
{
    bool _isBusy;

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

    public IAsyncCommand<int> ButtonCommand { get; }

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

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

AsyncCommand<TExecute, TCanExecute>

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

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

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

Sample project

AboutViewModel.

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

API