copy，mutableCopy和赋值之间有什么区别？

Question

我以为我理解了copy和mutableCopy之间的区别。但今天我怀疑自己。我还是不明白。

NSArray *arrayB = [NSArray arrayWithObject:@"a"];
NSArray *arrayA = [arrayB copy];
NSArray *arrayC = [arrayB mutableCopy];
NSArray *arrayD = arrayB;

当我对arrayA，arrayC或arrayD进行一些更改时，arrayB与更改的arrayA，arrayC和arrayD之间的更改是否相同？

Answer 1

NSArray *arrayB = [NSArray arrayWithObject:@"a"]; // Can't modify this NOW

NSArray *arrayA = [arrayB copy]; // Create another copy of Array B like XEROX. If you change in XEROX it does not reflect to original Copy

NSArray *arrayC = [arrayB mutableCopy]; // This is just Mutable copy so you can make changes in this and you have to change NSArray to NSMutableArray here as it the mutable copy.

NSArray *arrayD = arrayB;// Any change made in arrayD reflect to ArrayB but ArrayD is NSArray (immutable) so you can not make any changes in ArrayD

希望这有助于为您解决问题。

Answer 2

您无法对arrayA，arrayB或arrayD进行更改，它们是不可变的（并且arrayD不是新实例，它指向arrayB所执行的同一对象）。您只能将这些指针设置为指向其他数组。  如果你对arrayC（这里唯一可变的实例）进行了更改，那么不会，之前从中复制的arrayB将不会更改。