How is the Message Dispatch mechanism invoked in the system?

In iOS, the Message Dispatch mechanism is implemented through the message sending system in the Objective-C runtime. When a method is called on an object, dynamic method resolution and invocation occur.

Main steps of Message Dispatch:

1. The compiler transforms the method call into a message send using the objc_msgSend function.
2. At runtime, the implementation of the method is looked up in the object's method table.
3. If the method is found, it is called with the provided parameters.
4. If the method is not found, the mechanism for handling missing methods (e.g., forwardingTargetForSelector:) is invoked.

This allows for dynamic dispatch, message interception, and flexible design patterns such as delegation and proxies.

Example of invocation:

[obj doSomething]; // Compiled into objc_msgSend(obj, @selector(doSomething))

Thus, Message Dispatch is the core of dynamic method invocation in iOS, providing flexibility and extensibility of applications.