(二十一)[OC高效系列]理解NSCopying协议

1.NSCopying协议

若想令自己所写的对象具有拷贝功能，则需要实现NSCopying协议

• 实现copyWithZone方法
  • 方法中应该用全能初始化方法，来初始化待拷贝的对象

//.h
      @interface Person : NSObject <NSCopying>
          @property (nonatomic,copy) NSString *name;
          @property (nonatomic,readonly) NSArray *friends;
          @property (nonatomic,assign) int age;
          - (instancetype)initWithName:(NSString *)name age:(int)age;
      @end
    //.m
      @interface Person ()
        @property (nonatomic,readwrite,strong) NSMutableArray *friends;
      @end
      @implementation Person
        - (instancetype)initWithName:(NSString *)name age:(int)age
        {
            self = [super init];
            if (self) {
                self.name = name;
                self.age = age;
                _friends = [NSMutableArray array];
            }
            return self;
      }
      ... 
      - (id)copyWithZone:(NSZone *)zone{
          Person *p = [[[self class] allocWithZone:zone] initWithName:_name age:_age];
          return p;
      }
     @end

• 如果全能初始化不能满足要求，还应该手动的加上一些操作

        //.h
        @interface Person : NSObject <NSCopying>
            @property (nonatomic,copy) NSString *name;
            @property (nonatomic,readonly) NSArray *friends;
            @property (nonatomic,assign) int age;
            - (instancetype)initWithName:(NSString *)name age:(int)age;
        @end
        //.m
        @interface Person ()
          @property (nonatomic,readwrite,strong) NSMutableArray *friends;
        @end
        @implementation Person
        - (instancetype)initWithName:(NSString *)name age:(int)age
        {
              self = [super init];
                if (self) {
                    self.name = name;
                    self.age = age;
                    _friends = [NSMutableArray array];
                }
                return self;
      }
      ... 
      - (id)copyWithZone:(NSZone *)zone{
            Person *p = [[[self class] allocWithZone:zone] initWithName:_name age:_age];
            p->_friends = [_friends mutableCopy]; //额外的代码
    
            return p;
        }
    @end

• 如果自定义对象分为可变版本和不可变版本,那么就要同时实现NSCopying与NSMutableCopying协议

2.深拷贝与浅拷贝

• 深拷贝浅拷贝的对比图

  
  深拷贝与浅拷贝
• 复制对象时应该决定是深拷贝还是浅拷贝，一般情况下是浅拷贝,如果你所写的对象需要深拷贝，那么需要新增一个专门执行深拷贝的方法