gistfile1.cs

public class DelegateCommand : DelegateCommand<object>
{
    public DelegateCommand(Action executeMethod)
        : base(o => executeMethod())
    {
    }

    public DelegateCommand(Action executeMethod, Func<bool> canExecuteMethod)
        : base(o => executeMethod(), o => canExecuteMethod())
    {
    }
}

/// <summary>
/// A command that calls the specified delegate when the command is executed.
/// </summary>
/// <typeparam name="T"></typeparam>
public class DelegateCommand<T> : ICommand, IRaiseCanExecuteChanged
{
    private readonly Func<T, bool> _canExecuteMethod;
    private readonly Action<T> _executeMethod;
    private bool _isExecuting;

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

    public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod)
    {
        if ((executeMethod == null) && (canExecuteMethod == null))
        {
            throw new ArgumentNullException("executeMethod", @"Execute Method cannot be null");
        }
        _executeMethod = executeMethod;
        _canExecuteMethod = canExecuteMethod;
    }

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

    public void RaiseCanExecuteChanged()
    {
        CommandManager.InvalidateRequerySuggested();
    }

    bool ICommand.CanExecute(object parameter)
    {
        return !_isExecuting && CanExecute((T)parameter);
    }

    void ICommand.Execute(object parameter)
    {
        _isExecuting = true;
        try
        {
            RaiseCanExecuteChanged();
            Execute((T)parameter);
        }
        finally
        {
            _isExecuting = false;
            RaiseCanExecuteChanged();
        }
    }

    public bool CanExecute(T parameter)
    {
        if (_canExecuteMethod == null)
            return true;

        return _canExecuteMethod(parameter);
    }

    public void Execute(T parameter)
    {
        _executeMethod(parameter);
    }
}

I can't find CommandManager in my Prism 4.1 & Silverlight 5 Application. what is this? More I'm getting Error 5 Cannot find all types required by the 'async' modifier. Are you targeting the wrong framework version, or missing a reference to an assembly? D:\Projecttrial\Aminations\showHideOne\AsyncSupport\AsyncCommandBase.cs 53 9 showHideOne
Error.
How to resolve it and how I can use it in this scenerio
http://stackoverflow.com/questions/25001089/delegatecommand-async-support-prism-4-1/25001195#25001195

Where can I find IRaiseCanExecuteChanged description?

@AndreyMikhailov https://gist.github.com/JakeGinnivan/5166866