What is the meaning of delegate{ }

Question

Can someone please explain the meaning of delegate{ } below

public event EventHandler CanExecuteChanged = delegate { };

Also why does it eliminate the need for a null reference check on CanExecuteChanged, and what (if any) are the potential performance hits for using it.

Put simply, it's an empty method (so now `CanExecuteChanged` is bound to a ["NOOP"](https://en.wikipedia.org/wiki/NOP)) — Brad Christie, Aug 10 '15 at 18:08

score 8 · Answer 1 · answered Aug 10 '15 at 18:12

This is a sentinel value for parameterless delegate. It represents an anonymous method that does nothing.

It eliminates the need for null-checking because you can call such delegate without triggering a null reference exception.

Note: This trick becomes less relevant in C# 6.0, because the language provides an alternative syntax to calling delegates that may be null:

delegateThatCouldBeNull?.Invoke(this, value);

Above, null conditional operator ?. combines null checking with a conditional invocation.

score 3 · Answer 2 · answered Aug 10 '15 at 18:08

Here delegate { } is an Anonymous method block which will act as an event handler for the hooked up event. You can write necessary event processing logic here. Example below:

public event EventHandler CanExecuteChanged = delegate {
Console.WriteLine("CanExecuteChanged Event has been fired"); };

score 3 · Answer 3 · answered Aug 10 '15 at 18:09

delegate {} is an anonymous method with an empty body. It's a method that does nothing. The CanExecuteChanged event will always have a delegate assigned to it so it will never be null.

The only down side is that you've created a new delegate instance that will live in memory.

What is the meaning of delegate{ }

3 Answers3