Action<> and Func<> delegates

these new generic delegates were added in .NET 3.5 for LINQ, but they’re also very useful in your own classes. Action<> allows you to specify types for up to 4 parameters and returns void, and Func<> does the same except you can also specify a return type. if you look at the LINQ extension methods, you’ll see these delegates extensively.

so for example, if you needed a delegate that returned void and took no parameters, you’d have to write something like:

public delegate void VoidDelegate();

public event VoidDelegate MyEvent;

so what you end up with is repetitive declarations of such a VoidDelegate delegate in lots of classes. now, you can just use the Action<> delegate to do this (Action<> works in any case where you return void and take up to 4 parameters):

public event Action MyEvent;

same goes for Func<>. before, you’d have to create a delegate for each specific set of input variable and return types:

public delegate string TakeTwoStringsAndReturnStringDelegate(string String1, string String2);

and then call it like:

return (String)Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Normal,
 (TakeTwoStringsAndReturnStringDelegate)delegate 
 { 
  return TakeTwoStringsAndReturnString("1", "2"); 
 } 
);

now you can use Func<> instead (Func<> also works for up to 4 parameters):

return (String)Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Normal,
 (Func<String, String, String>)delegate 
 { 
  return TakeTwoStringsAndReturnString("1", "2"); 
 } 
);

there are probably still times when you’ll want to create your own delegate, but these two generics are very useful for filling in the gaps—