如何在Objective-C中正确子类化委托属性？ [英] How to properly subclass a delegate property in Objective-C?

问题描述

在对类进行子类化时，我还希望子类的父类的子类，因为子类现在具有其他功能。这样做的最佳方法是什么？如果我只是在子类中使用相同的名称声明另一个委托属性，我会收到警告属性类型'id'与继承自'ParentClass'的类型'id'不兼容

In subclassing a class, I want to also subclass a delegate of the parent class given that the subclass now has additional functionality. What's the best way to go about doing this? If I just declare another delegate property in the subclass with the same name I would get a warning "Property type 'id' is incompatible with type 'id' inherited from 'ParentClass'

推荐答案

鉴于此示例产生警告：

// Class A
@protocol ClassADelegete;

@interface ClassA : NSObject
@property (nonatomic, weak) id<ClassADelegete> delegate;
@end

@protocol ClassADelegete <NSObject>
- (void)classADidSomethingInteresting:(ClassA *)classA;
@end

// Class B
@protocol ClassBDelegete;

@interface ClassB : ClassA
@property (nonatomic, weak) id<ClassBDelegete> delegate; // Warning here
@end

@protocol ClassBDelegete <ClassADelegete>
- (void)classBDidSomethingElse:(ClassB *)classB;
@end

删除警告的两个解决方案是。

Two solutions that remove the warning are.

1）在子类中，将协议定义放在类定义之前。这就是 UITableView.h 中的 UITableViewDelegate ：

1) In the subclass, place the protocol definition before the class definition. This is what UITableViewDelegate in UITableView.h does:

// Class B
@class ClassB;

@protocol ClassBDelegete <ClassADelegete>
- (void)classBDidSomethingElse:(ClassB *)classB;
@end

@interface ClassB : ClassA
@property (nonatomic, weak) id<ClassBDelegete> delegate;
@end

2）在子类中，添加原始协议和新协议：

2) In the subclass, add the original protocol alongside the new one:

// Class B
@protocol ClassBDelegete;

@interface ClassB : ClassA
@property (nonatomic, weak) id<ClassADelegete, ClassBDelegete> delegate;
@end

@protocol ClassBDelegete <ClassADelegete>
- (void)classBDidSomethingElse:(ClassB *)classB;
@end

我认为（1）就像苹果这样做，Option（ 2）删除警告，但我没有编译并以这种方式运行任何设置。

I assume (1) works as Apple do it this way, Option (2) removes the warning but I haven't compiled and run anything setup this way.

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