[Objective-C] basic concepts and usage of protocols in OC

Basic concepts of Protocol

The Declaration of the Protocol looks similar to the interface of a class in Java, but unlike the interface, the Protocol does not have a parent class and cannot define instance variables.

A protocol is a special program design structure used to declare methods implemented by other classes. Protocols are useful in the following scenarios:

 

• Methods that need to be implemented by other classes
• Declare an unknown class Interface
• Communication between two classes

  Basic Features of the Protocol

   

  • Methods that can be implemented by any class
  • The Protocol itself is not a class. It defines an interface that can be implemented by other classes.
  • Protocol can also be used for the category (not used much)

    Keyword in the Protocol

     

    • @ Required: indicates the method that must be implemented forcibly.
    • @ Optional: indicates a selective implementation method.

      Example:

      Agreement statement:

       

      // Protocol declaration # import
             
              
      @ Protocol OneProtocol
              
               
      // Optional implementation method: @ optional-(void) optionalMethod1;-(void) optionalMethod2; // required implementation method: @ required-(void) requiredMethod1; @ end // use the Protocol (Test. h) # import "OneProtocol. h "@ interface Test: NSObject
               
              
             

       

       

      Protocol implementation method:

       

      # Import "Test. h "@ implementation Test-(void) optionalMethod1 {// optional implementation method 1}-(void) optionalMethod2 {// optional implementation method 2}-(void) requiredMethod1 {// required implementation method 2} @ end

      Main. m method:

       

       

       Test *test=[[Test alloc]init];        [test optionalMethod1];        [test optionalMethod2];        [test requiredMethod1];        [test autorelease];