__week and autorelease pool in ARC in Xcode 4.2

转载于 2012-01-08 01:27:28 发布 · 1.3k 阅读

文章标签：

#xcode #string #reference #null

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本文探讨了Objective-C中弱引用变量与自动释放池的交互作用，并通过具体代码示例展示了如何正确使用弱引用避免内存管理问题。

NSString __weak *string;
@autoreleasepool {
        string = [NSString stringWithFormat:@"%@", @"AAA"];
}

NSLog(@"string: %@", string);

it outputs as the following what you want.

string: (null)

Thus,

string = [NSString stringWithString:@"AAA"];

is same as

string = @"AAA";

the constant string literal that is not allocated in the heap.

EDITED:

str variable has still strong reference for the autoreleased object.

The following code is what exactly you want.

NSString __weak *string;
{
    NSString __strong *str;
    @autoreleasepool {
        str = [NSString stringWithFormat:@"%@", @"AAA" ];
        string = str;
    }
}
NSLog(@"string: %@", string);

And

NSString __weak *string;
@autoreleasepool {
    NSString __strong *str;
    str = [NSString stringWithFormat:@"%@", @"AAA" ];
    string = str;
}
NSLog(@"string: %@", string);