關於深拷貝淺拷貝

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.
以上三句出自於蘋果官方文檔 Collections.pdf。

意思大體以下：

有兩種類型的對象拷貝，淺拷貝和深拷貝。正常的拷貝，生成一個新的容器，但倒是和原來的容器共用內部的元素，這叫作淺拷貝。深拷貝不只生成新的容器，還生成了新的內部元素。

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.
以上兩句出自於蘋果官方文檔 CFMemoryMgmt.pdf。

OK，有官方文檔爲證。淺拷貝複製容器，深拷貝複製容器及其內部元素。

淺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]];

//如上代碼雖然使用的是mutableCopy，但依舊是淺copy，與使用copy意義是同樣的其實；所以僅僅是copy的數組容器，並無開闢新空間容納數組內的數據，所以newArray中數據更改時，對應的self.dataArr的數據也是在更改；

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";
    }
    
    //   該代碼就是self.dataArr替換更改過的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的實現方式，所以從新開闢新空間以供數組元素存儲，所以newArray中model發生改變時，並不會影響self.dataArr的數據。

不過使用深copy時須要注意一點：須要對自定義的model重寫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;
}

 

最後來總結一下：

全部系統容器類的copy或mutableCopy方法，都是淺拷貝！！！

淺拷貝複製容器，深拷貝複製容器及其內部元素