Concrete Delegate vs EventHandler for Events

Well, as always it depends on what you need. The EventHandler type is just a predefined general purpose delegate type that is commonly used by most GUI controls of the .NET framework. As most events have some object that is responsible for raising the event (the "sender") and often an event requires some parameters. The EventHandler type is just a generic way to maintain compatibility with other systems.

Your line:

 public delegate void Event_Handler ();

Just declares a new delegate type with no parameters and no return type. You would only need to declare that delegate once for your entire project.

However you don't need to declare that delegate at all, since there is already the System.Action delegate type which is exactly the same as your type. There are also generic versions of that type where you can easily specify parameter types.

For example Action<Vector3, float> represents a delegate like this:

 public delegate void DelegateTypeName (Vector3 v, float f);

So if you just want to declare an event with no parameters you can simply do:

 public event System.Action Some_Event;

Furthermore there's also the "Func" type which represents a delegate with a return type.

 Func<int, int, string>

will represent

 public delegate string DelegateTypeName (int i1, int i2);