removeObjectAtIndex 导致“消息发送到释放的实例”

Question

我正在将一些代码转换为 ARC。代码在 NSMutableArray 中搜索元素，然后查找、删除并返回该元素。问题是元素在“removeObjectAtIndex”后立即被释放：

- (UIView *)viewWithTag:(int)tag
{
    UIView *view = nil;
    for (int i = 0; i < [self count]; i++)
    {
        UIView *aView = [self objectAtIndex:i];
        if (aView.tag == tag) 
        {
            view = aView;
            NSLog(@"%@",view); // 1 (view is good)
            [self removeObjectAtIndex:i];
            break;
        }
    }
    NSLog(@"%@",view); // 2 (view has been deallocated)
    return view;
}

当我运行它时，我得到了

*** -[UIView respondsToSelector:]: message sent to deallocated instance 0x87882f0

在第二条日志语句中。

在 ARC 之前，我在调用 removeObjectAtIndex: 之前小心地保留了对象，然后自动释放它。我如何告诉 ARC 做同样的事情？

Answer 1

使用__autoreleasing 限定符声明UIView *view 引用，如下所示：

- (UIView *)viewWithTag:(int)tag
{
    __autoreleasing UIView *view;
    __unsafe_unretained UIView *aView;

    for (int i = 0; i < [self count]; i++)
    {
        aView = [self objectAtIndex:i];
        if (aView.tag == tag) 
        {
            view = aView;
            //Since you declared "view" as __autoreleasing,
            //the pre-ARC equivalent would be:
            //view = [[aView retain] autorelease];

            [self removeObjectAtIndex:i];
            break;
        }
    }

    return view;
}

__autoreleasing 会给你正是你想要的，因为在分配时，新指针被保留、自动释放，然后存储到左值中。

见ARC reference