Delegate:
1. delegate is the function pointer. Type-safe function pointer (this restriction is not found in C)
2. A delegate can be considered as a method signature of a certain type. This type is only applicable to the return value and method parameters. That is, the method parameter format, sequence, number, and return type are the same, regardless of its static/instance, public/private/Internal /..., it can be defined as a type of Delegate (called by the delegate), that is, the delegate instance, so there is no static, in its Declaration
3. Delegate inheritance structure: DeleGate <-- system. multicastdelegate <-- system. Delegate. When a multicast delegate is used, the delegate type must be void (because the return type of each delegate method is unknown)
4. The methods in multicast delegation are called in sequence (FIFO), so it is best to have no dependency between methods.
Event:
1. The event depends on the delegate, which processes the eventProgramRegister with the delegate.
2. events can be associated with multiple delegates (instances of the same type). These delegates have no execution sequence. Of course, the event handler is also of the void type.
