NSCopying协议

NSCopying协议：

@protocol NSCopying

- (id)copyWithZone:(nullable NSZone *)zone; //实例方法

@end

@protocol NSMutableCopying

- (id)mutableCopyWithZone:(nullable NSZone *)zone; //实例方法

@end

分为不可变和可变两种拷贝。zone参数是被忽略的，因此可以不管。

实现：

具体怎么实现直接参考知名开源框架的写法，跟着大佬来肯定没错。

@property (nonatomic, strong, nullable) NSSet <NSData *> *pinnedCertificates;
- (instancetype)copyWithZone:(NSZone *)zone {
    AFSecurityPolicy *securityPolicy = [[[self class] allocWithZone:zone] init];
    securityPolicy.SSLPinningMode = self.SSLPinningMode; //值类型，直接赋值就可以了。
    securityPolicy.allowInvalidCertificates = self.allowInvalidCertificates;
    securityPolicy.validatesDomainName = self.validatesDomainName;
    securityPolicy.pinnedCertificates = [self.pinnedCertificates copyWithZone:zone]; //对象类型调用copyWithZone，需要确保对象已经实现了copy协议。这里不需要可变所以调用copyWithZone

    return securityPolicy;
}


@property (readwrite, nonatomic, strong) NSMutableDictionary *mutableHTTPRequestHeaders;
- (instancetype)copyWithZone:(NSZone *)zone {
    AFHTTPRequestSerializer *serializer = [[[self class] allocWithZone:zone] init];
    dispatch_sync(self.requestHeaderModificationQueue, ^{
      	//这里需要可变所以调用mutableCopyWithZone
        serializer.mutableHTTPRequestHeaders = [self.mutableHTTPRequestHeaders mutableCopyWithZone:zone];
    });
    serializer.queryStringSerializationStyle = self.queryStringSerializationStyle;
    serializer.queryStringSerialization = self.queryStringSerialization;

    return serializer;
}

//---AFHTTPResponseSerializer
#pragma mark - NSCopying

- (instancetype)copyWithZone:(NSZone *)zone {
    AFHTTPResponseSerializer *serializer = [[[self class] allocWithZone:zone] init]; //不能写死为[AFHTTPResponseSerializer allocWithZone:zone]
    serializer.acceptableStatusCodes = [self.acceptableStatusCodes copyWithZone:zone];
    serializer.acceptableContentTypes = [self.acceptableContentTypes copyWithZone:zone];

    return serializer;
}

//---AFCompoundResponseSerializer:AFHTTPResponseSerializer
@property (readwrite, nonatomic, copy) NSArray *responseSerializers;
- (instancetype)copyWithZone:(NSZone *)zone {
    AFCompoundResponseSerializer *serializer = [super copyWithZone:zone];
    serializer.responseSerializers = self.responseSerializers; //responseSerializers属性是copy，所以可以直接赋值。setter方法里会调用copy.

    return serializer;
}

如果父类实现了则必须调用super，否则会丢失信息：

- (instancetype)copyWithZone:(NSZone *)zone {
    AFPropertyListResponseSerializer *serializer = [super copyWithZone:zone]; //调用super
    serializer.format = self.format;
    serializer.readOptions = self.readOptions;

    return serializer;
}

注意：NSObject是没有实现copy协议的。

NSObject下有两个实例方法：

- (id)copy;
- (id)mutableCopy;

他们仅仅是返回对应的copy协议方法的值。如果对象没实现则会崩溃。这两个方法只是方便使用。

This is a convenience method for classes that adopt the NSCopying protocol. An exception is raised if there is no implementation for copyWithZone:.
NSObject does not itself support the NSCopying protocol. Subclasses must support the protocol and implement the copyWithZone: method. A subclass version of the copyWithZone: method should send the message to super first, to incorporate its implementation, unless the subclass descends directly from NSObject.