iOS：如何使用NSMutableArray

Question

In my code, I must to store an array inside another array: What's the best way?

first:

NSArray *arrayTemp = myArray;

second:

NSMutableArray *arrayTemp = [[NSMutableArray alloc]init];
[arrayTemp addObjectsFromArray:myArray]; 
...instruction....
[arrayTemp release];

Answer 1

By doing arrayTemp = myArray , you declare arrayTemp as a new pointer to your existing array myArray . That's not a copy (if you put X in myArray[42], arrayTemp[42] will also be X).

The second variant looks like you're doing a copy of your array, but still the array's values are copied by reference (by pointer), when you seem to need a copy "by value".

What you should try is simply:

NSArray *arrayCopy = [myArray copy];

Beware: from a memory management point of view, this is equivalent to a retain or a alloc/init : you should release your arrayCopy after use.