Any WinRT iCommand/CommandBinding implementaiton samples out there?

Question

Abstracting commands into the View Model is a valuable practice with XAML/MVVM projects. I get that. And, I see ICommand in in WinRT; but, how do we implement it? I haven't found a sample that actually works. Anyone know?

Answer 1

My all time favorite has to be the DelegateCommand provided by the Microsoft Patterns and Practices team. It allows you to create a typed command:

MyCommand = new DelegateCommand<MyEntity>(OnExecute);
...
private void OnExecute(MyEntity entity)
{...}

It also provides a way to raise the CanExecuteChanged event (to disable/enable the command)

MyCommand.RaiseCanExecuteChanged();

Here's the code:

public class DelegateCommand<T> : ICommand
{
    private readonly Func<T, bool> _canExecuteMethod;
    private readonly Action<T> _executeMethod;

    #region Constructors

    public DelegateCommand(Action<T> executeMethod)
        : this(executeMethod, null)
    {
    }

    public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod)
    {
        _executeMethod = executeMethod;
        _canExecuteMethod = canExecuteMethod;
    }

    #endregion Constructors

    #region ICommand Members

    public event EventHandler CanExecuteChanged;

    bool ICommand.CanExecute(object parameter)
    {
        try
        {
            return CanExecute((T)parameter);
        }
        catch { return false; }
    }

    void ICommand.Execute(object parameter)
    {
        Execute((T)parameter);
    }

    #endregion ICommand Members

    #region Public Methods

    public bool CanExecute(T parameter)
    {
        return ((_canExecuteMethod == null) || _canExecuteMethod(parameter));
    }

    public void Execute(T parameter)
    {
        if (_executeMethod != null)
        {
            _executeMethod(parameter);
        }
    }

    public void RaiseCanExecuteChanged()
    {
        OnCanExecuteChanged(EventArgs.Empty);
    }

    #endregion Public Methods

    #region Protected Methods

    protected virtual void OnCanExecuteChanged(EventArgs e)
    {
        var handler = CanExecuteChanged;
        if (handler != null)
        {
            handler(this, e);
        }
    }

    #endregion Protected Methods
}

Answer 2

Check out RelayCommand class (only METRO code). The NotifyPropertyChanged class can be found here. The NotifyPropertyChanged class is only used to allow bindings on CanExecute and update it with RaiseCanExecuteChanged.

The original relay command class can be found here