A summary of the SEL and selector principles of "iOS development"

introduction of Selector (selector) A selector is a name used to select a method to execute for an object, or to replace the name of a unique identifier for that name when compiling the source code. A selector does not do anything by itself. It simply identifies a method. The compiler ensures that the selector is unique, except that the method name of the selector is different from the normal string. What makes a selector useful is (at runtime) it is like a dynamic function pointer , which automatically points to a method's implementation for a given name and applies to any class it uses. Suppose you have a Run method selector and a class dog, Student. The selector can use an instance of each class to invoke its running method, even if the implementation of each class may be different. second, get a selector The type of the compiled selector is the SEL. There are two common ways to get selectors: (1) When compiling, the compiler instruction @selector to obtain.

SEL aselector = @selector (methodname); (2) at runtime, the string is used to get a method name nsselectorfromstring

SEL aselector = nsselectorfromstring (@ "methodname"); iii. use of selector Use the selector that you have created. You can invoke a method by Performselector:

Create a Run method selector
SEL aselector = @selector (run);

//through Performselector: To invoke the run method
[Adog Performselector:aselector] of the object;
[Anstudent Performselector:aselector]; Note: A selector is typically created on its own under special circumstances, such as when you expose a button's click event to the outside class to implement its click Method,-(void) Addtarget: (ID) Target action: (SEL) Action; This is where @selector is used.