关于深拷贝浅拷贝

There are two kinds of object copying: shallow copies and deep copies. The normal copy is a shallow copy that produces a new collection that shares ownership of the objects with the original. Deep copies create new objects from the originals and add those to the new collection.
以上三句出自于苹果官方文档 Collections.pdf。

意思大致如下：

有两种类型的对象拷贝，浅拷贝和深拷贝。正常的拷贝，生成一个新的容器，但却是和原来的容器共用内部的元素，这叫做浅拷贝。深拷贝不仅生成新的容器，还生成了新的内部元素。

In the case of these objects, a shallow copy means that a new collection object is created, but the contents of the original collection are not duplicated—only the object references are copied to the new container. 
A deep copy duplicates the compound object as well as the contents of all of its contained objects.
以上两句出自于苹果官方文档 CFMemoryMgmt.pdf。

OK，有官方文档为证。浅拷贝复制容器，深拷贝复制容器及其内部元素。

浅copy示例：

NSMutableArray *newArray = [self.dataArr mutableCopy];
    WeekModel *model = [newArray objectAtIndex:indexPath.row];
    
    if ([model.isCheck isEqualToString:@"1"]) {
        model.isCheck = @"0";
    } else {
        model.isCheck = @"1";
    }
    ChooseCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    [cell setCheckd:[self.dataArr objectAtIndex:indexPath.row]];

//如上代码虽然使用的是mutableCopy，但依旧是浅copy，与使用copy意义是一样的其实；因此仅仅是copy的数组容器，并没有开辟新空间容纳数组内的数据，因此newArray中数据更改时，对应的self.dataArr的数据也是在更改；

深copy示例：

　　//深copy
    NSMutableArray *newArray = [[NSMutableArray alloc] initWithArray:self.dataArr copyItems:YES];
    
    WeekModel *model = [newArray objectAtIndex:indexPath.row];
    
    if ([model.isCheck isEqualToString:@"1"]) {
        model.isCheck = @"0";
    } else {
        model.isCheck = @"1";
    }
    
    //   该代码就是self.dataArr替换更改过的model
     [self.dataArr replaceObjectAtIndex:indexPath.row withObject:model];
    
    ChooseCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    [cell setCheckd:[self.dataArr objectAtIndex:indexPath.row]];

如上就是深copy的实现方式，因此重新开辟新空间以供数组元素存储，因此newArray中model发生改变时，并不会影响self.dataArr的数据。

不过使用深copy时需要注意一点：需要对自定义的model重写copyWithZone:方法

//.h文件
@interface WeekModel : NSObject

@property (strong, nonatomic) NSString *weekId;
@property (strong, nonatomic) NSString *weekName;
@property (assign, nonatomic) NSString *isCheck;

- (instancetype)initWithId:(NSString *)weekId weekName:(NSString *)weekName isCheck:(NSString *)isCheck;

- (id)copyWithZone:(NSZone *)zone;

//.m文件
- (instancetype)initWithId:(NSString *)weekId weekName:(NSString *)weekName isCheck:(NSString *)isCheck {
    self = [super init];
    if (self) {
        self.weekId = weekId;
        self.weekName = weekName;
        self.isCheck = isCheck;
    }
    return self;
}

- (id)copyWithZone:(NSZone *)zone {
    
    WeekModel *model = [[WeekModel allocWithZone:zone] init];
    model.weekId = self.weekId;
    model.weekName = self.weekName;
    model.isCheck = self.isCheck;
    return model;
}

 

最后来总结一下：

所有系统容器类的copy或mutableCopy方法，都是浅拷贝！！！

浅拷贝复制容器，深拷贝复制容器及其内部元素