NSCopying协议练习

小灰灰 2022-08-18 11:44 86阅读 0赞

#import <Foundation/Foundation.h>
    
    @interface TestCopyProtocol : NSObject<NSCopying>
    
    @property (nonatomic,readwrite) NSInteger index;
    @property (nonatomic,readwrite,copy) NSString* str;
    
    - (id)copyWithZone:(NSZone *)zone;
    - (NSString *)description;
    
    @end
    
    @interface TestCopyProtocolChild : TestCopyProtocol<NSCopying>
    
    @property(nonatomic,readwrite,copy) NSString* myStr;
    
    - (id)copyWithZone:(NSZone *)zone;
    - (NSString *)description;
    @end

#import "TestCopyProtocol.h"
    #import <UIKit/UIKit.h>
    @implementation TestCopyProtocol
    
    -(id)copyWithZone:(NSZone *)zone
    {
        id copy = [[[self class] alloc] init];
        
        if (copy) {
            [copy setIndex:self.index];
            [copy setStr:self.str];
        }
        return copy;
    }
    
    -(NSString*)description
    {
        return [NSString stringWithFormat:@"super des is %@ int is %ld, str is %@",
               [super description], self.index, self.str];
    }
    
    @end
    
    @implementation TestCopyProtocolChild

-(id)copyWithZone:(NSZone *)zone
    {
        id copy = [super copyWithZone:zone];
        if (copy) {
            [copy setMyStr:self.myStr];
        }
        return copy;
    }
    
    -(NSString*)description
    {
        return [NSString stringWithFormat:@"super des is %@ myStr is %@",
                [super description], self.myStr];
    }
    @end

调用

TestCopyProtocol* t = [[TestCopyProtocol alloc]init];
        t.index = 5;
        t.str = @"hello";
        TestCopyProtocol* t1 = [t copy];
        t.str = @"world";
        NSLog(@"%@",t);
        NSLog(@"%@",t1);
        
        
        TestCopyProtocolChild* t2 = [t copy];
        NSLog(@"%@",t2.class);//这个地方是个坑吧，t2怎么就变成了TestCopyProtocol？
        TestCopyProtocolChild* t3 = [[TestCopyProtocolChild alloc] init];
        t3.index = 4;
        
        t3.myStr = @"w";
        TestCopyProtocolChild* t4 = [t3 copy];
        NSLog(@"%@",t4);

总结下吧：

1，写这个协议的时候，得看下类的上层类（可能是父类以上的类）有没有实现这个方法copyWithZone，也就是找到alloc对象的地方。

2，如果父类实现了这个协议，子类就不用写了，直接覆盖copyWithZone即可（协议的实现应该都是这样吧，和接口道理类似）。

3，调用的时候，对象变量的类型是根据被copy的类型决定的，不是声明的类型。