Question

I am using this code to make a Simple Command:

public class SimpleCommand : ICommand
{
    public Predicate<object> CanExecuteDelegate { get; set; }
    public Action<object> ExecuteDelegate { get; set; }

    #region ICommand Members

    public bool CanExecute(object parameter)
    {
        if (CanExecuteDelegate != null)
            return CanExecuteDelegate(parameter);
        return true;// if there is no can execute default to true
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public void Execute(object parameter)
    {
        if (ExecuteDelegate != null)
            ExecuteDelegate(parameter);
    }

    #endregion
}

I did not write this. But I enjoy using it. When I use it it ends up being like this:

// This is the value that gets set to the command in the UI
public SimpleCommand DoSomethingCommand { get; set; }


public DoSomethingCommandConstructor()
{
    DoSomethingCommand = new SimpleCommand
                        {
                            ExecuteDelegate = x => RunCommand(x)
                        };
}

private void RunCommand(object o)
{
    // Run the command.
}

The only problem with this is that the parameter of RunCommand is an object. I think I have been spoiled by generics. I always want the IDE/compiler to just know what the type I am working with is with out casting.

Is it possible to change this SimpleCommand class to be implemented using generics?

Answer 1

Sure. Was gonna point you to Prism’s implementation, but CodePlex source tab seems to not be working. It would look something like:

public class SimpleCommand<T> : ICommand
{
    public Predicate<T> CanExecuteDelegate { get; set; }
    public Action<T> ExecuteDelegate { get; set; }

    #region ICommand Members

    public bool CanExecute(object parameter)
    {
        if (CanExecuteDelegate != null)
            return CanExecuteDelegate((T)parameter);
        return true;// if there is no can execute default to true
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

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

    #endregion
}

Incidentally, your usage of SimpleCommand in your question is a little roundabout. Instead of this:

DoSomethingCommand = new SimpleCommand
                    {
                        ExecuteDelegate = x => RunCommand(x)
                    };

You could just have:

DoSomethingCommand = new SimpleCommand
                    {
                        ExecuteDelegate = this.RunCommand
                    };

Specifying a lambda is really only useful if you’re doing the work inline like this:

DoSomethingCommand = new SimpleCommand
                    {
                        ExecuteDelegate = o => this.SelectedItem = o,
                        CanExecuteDelegate = o => o != null
                    };