IOS深拷貝和淺拷貝

第一、淺拷貝：

    Car *car=[[[self class] allocWithZone:zone] init];    car.engine=_engine;    car.name=_name;    car.weight=_weight;    return car;

測試代碼：

 Car *car = [[Car alloc] init];        Engine *engine = [[Engine alloc] init];        car.engine = engine;        [engine release];        //NSLog(@"engine retaincount is %lu",[engine retainCount]);        car.name = @"奧迪";        car.weight = @1000;        Car *car2=[car copy];       // NSLog(@"car2 retaincount is %lu",[car2 retainCount]);        NSLog(@"car %@,car2:%@",car.engine,car2.engine);

輸出結果：

car ,car2:

可以看出淺複製只是複製指標，並沒有建立新的記憶體空間

第二、深拷貝：

- (id)copyWithZone:(NSZone *)zone {    /***淺拷貝**/    Car *car=[[[self class] allocWithZone:zone] init];    Engine *engineCopy=[[_engine copy] autorelease];    car.engine=engineCopy;        NSString *namecopy=[[_name copy] autorelease];    car.name=namecopy;        NSNumber *weightcopy=[[_weight copy] autorelease];    car.weight=weightcopy;    return car;}

測試代碼：

Car *car = [[Car alloc] init];        Engine *engine = [[Engine alloc] init];        car.engine = engine;        [engine release];        //NSLog(@"engine retaincount is %lu",[engine retainCount]);        car.name = @"奧迪";        car.weight = @1000;        Car *car2=[car copy];       // NSLog(@"car2 retaincount is %lu",[car2 retainCount]);        NSLog(@"car %@,car2:%@",car.engine,car2.engine);

結果：

car ,car2:

開闢了新的空間,zone代表一塊記憶體空間

 Car *car=[[[self class] allocWithZone:zone] init];

注意上述代碼用的是【self class】，而不是car，因為如果是用car，那麼car的子類在調用此方法去實現copy協議時，就會出現記憶體問題

另外，當子類繼承了父類時，他繼承了父類的一切屬性，包括要實現的協議

第三、NSFoundation，當我們copy的時一個不可變對象時，預設的copy都是淺拷貝,相當於retain

        NSArray *array =[NSArray arrayWithObjects:@"one",@"two",@"three", nil];        NSArray *array1 = [array copy];        NSLog(@"%p",array);        NSLog(@"%p",array1);        NSLog(@"the retaincount is %lu",[array retainCount]);

輸出結果：

copyDemo1[673:303] 0x10010a5d0

2013-12-28 20:01:10.969 copyDemo1[673:303] 0x10010a5d0

2013-12-28 20:01:10.969 copyDemo1[673:303] the retaincount is 2

注意retaincount會增加

當使用mutableCopy時，不管對象是否可變，都會實現深拷貝

        NSArray *array =[NSArray arrayWithObjects:@"one",@"two",@"three", nil];        NSMutableArray *array1 = [array mutableCopy];        NSLog(@"%p",array);        NSLog(@"%p",array1);        NSLog(@"the retaincount is %lu",[array retainCount]);

結果：

copyDemo1[695:303] 0x10010a5d0

2013-12-28 20:07:08.570 copyDemo1[695:303] 0x10010b260

2013-12-28 20:07:08.570 copyDemo1[695:303] the retaincount is 1

第四、retain相當於兩個對象指向同一個指標

        NSMutableArray *array1 = [[NSMutableArray alloc] initWithObjects:@"one",@"two",@"three",@"foure", nil];        NSMutableArray *array2 = [array1 retain];        [array2 removeLastObject];        NSLog(@"%@",array1);        NSLog(@"the retaincount is %ld",array2.retainCount);

結果：

2013-12-28 20:13:02.915 copyDemo1[736:303] (    one,    two,    three)2013-12-28 20:13:02.917 copyDemo1[736:303] the retaincount is 2