How to accomplish a weak delegate，and the protocol in swift How to inherit ？- 2018-01-11

How to accomplish a weak delegate，and the protocol in swift How to inherit ？

• The way to accomplish a weak delegate，and that protocol‘s inheritance in swift ？

• A smaple:

    protocol ProtocolNameDelegate {
        // Protocol stuff goes here
    }
    
    class SomeClass {
        weak var delegate: ProtocolNameDelegate? \\ error occured
    }           
  

  • error:

    • 当你在swift中为代理设置weak属性以便于避免循环引用的时候，报编译错误

        'weak' may only be applied to class and class-bound protocol types, not 'MyImageCellDelegate'
      

  • Why did this error occur?

    • 因为在swift中协议是不仅可以被引用类型实现，也可以被值类型引用，但是weak只能用来修饰引用类型，所以在使用weak修饰没有加任何限定词的协议时报错，我们将如何使用weak修饰协议定义的类型属性呢

      • 有如下三种方法：

          protocol ProtocolNameDelegate: class {
              // Protocol stuff goes here
          }
          
          or
          
          protocol ProtocolNameDelegate: NSObjectProtocol {
              // Protocol stuff goes here
          }
          
          or
          
          @objc protocol ProtocolNameDelegate {
              // Protocol stuff goes here
          }
          
          Although, under code is successed to build, but which one is the best?
          
          class SomeClass {
              weak var delegate: ProtocolNameDelegate?
          }
        

      • which one is the best way to use the weak keywords with Protocol Type Parameter ?

        • NSObjectProtocol is equal to NSObject Protrocol in Objective-C
        • @objc keyword is define the type as objective-c types
        • class keyword limit the protocol only used for reference type in swift

        All in all ， NSObjectProtocol > class > @objc