Question

从弱强引用中可以理解的是：

强者和弱者都引用了一个对象。
虽然strong不再引用该对象，但弱指针将丢失其引用的对象。

然后我用这个例子（取自SO中的其他线程）尝试了我的完整代码：

- (void)viewDidLoad
{
  [super viewDidLoad];

  NSDate* date = [[NSDate alloc] init]; // date stays around because it's __strong
  __weak NSDate* weakDate = date;

  // Here, the dates will be the same, the second pointer (the object) will be the same
  // and will remain retained, and the first pointer (the object reference) will be different
  NSLog(@"Date(%p/%p): %@", &date, date, date);
  NSLog(@"Weak Date(%p/%p): %@", &weakDate, weakDate, weakDate);

  // This breaks the strong link to the created object and the compiler will now
  // free the memory. This will also make the runtime zero-out the weak variable
  date = nil;

  NSLog(@"Date(%p/%p): %@", &date, date, date);
  NSLog(@"Weak Date(%p/%p): %@", &weakDate, weakDate, weakDate);
}

我只是意识到这没有给出预期的结果：

Date(0xbfffdccc/0x713df20): 2013-12-04 04:19:30 +0000
Weak Date(0xbfffdcc8/0x713df20): 2013-12-04 04:19:30 +0000
Date(0xbfffdccc/0x0): (null)
Weak Date(0xbfffdcc8/0x713df20): 2013-12-04 04:19:30 +0000

为什么weakDate的第二次打印仍然打印出来？我有错误的理解吗？

注意：

我在 iOS模拟器iOS 6.0

中测试的 Xcode 4.5.1 中使用 ARC

弱与强参考

0 个答案: