Summary of several common IOS callback Methods

1. function pointer-the most essential and underlying call

2. Block syntax-package, essentially called through function pointers

3.tar get-action mode-encapsulate the function pointer (use the OC Function Name string to search for the function pointer through sel-@ selector ), do not know the function to be called back (essentially a function pointer)

4. Delegate protocol mode-encapsulate the function pointer (use the OC Function Name string to find the function pointer through sel-@ selector) and know the function to be called back (essentially a function pointer)

5. Message notification-send messages to multiple objects using a single object (essentially a function pointer)