初始化内部块后对象变为零

Question

这是我的代码：

    __block UIButton buttonOne;
    __block UIButton buttonTwo;
    - (UIView *)addressOptionView
    {
        if (!_addressOptionView) {
            _addressOptionView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.view.frame), addressButtonArray.count * BasedAdditionForSegment)];

            void (^setupButton)(UIButton *, NSString *, NSInteger) = ^
            void (UIButton *button, NSString *title, NSInteger idx) {
                if (!button)
                    button = [[UIButton alloc] init];
                button.frame = ({
                    CGRect frame = _addressOptionView.bounds;
                    frame.origin.x += 20;
                    frame.size.width -= 40;
                    frame.origin.y = idx * BasedAdditionForSegment;
                    frame.size.height = BasedAdditionForSegment;
                    frame;
                });
                [button setTitle:title forState:UIControlStateNormal];
            };
            setupButton(buttonOne, addressButtonArray[0], 0);
            setupButton(buttonTwo, addressButtonArray[1], 1);

            DebugLog(@"%@", buttonOne);
            [_addressOptionView addSubview:buttonOne];
            [_addressOptionView addSubview:buttonTwo];
        }
        return _addressOptionView;
    }

buttonOne和buttonTwo不是属性。

在我调用addressOptionView getter ，这两个按钮会立即被释放，因此它们不会显示在视图中（我想在NSLog时为nil）。

我将setupButton块更改为@property ，它也不起作用。 将两个按钮更改为@property也不起作用。

但是，当我将setupButton块更改为

UIButton * (^setupButton)(NSString *, NSInteger)

确实出现了两个按钮，但是以后我无法以其他方法访问它们（已经为nil ）。

有人可以简要说明我做错了什么吗？ 我该如何运作？ 谢谢。

Answer 1

@implementation SomeObject {
  // do not make these __block types
  UIButton* _buttonOne;
  UIButton* _buttonTwo;
}

- (UIView *)addressOptionView
{
  // most of method removed for brevity, see question
  void (^setupButton)(UIButton*__autoreleasing*, NSString *, NSInteger) = ^
   void (UIButton*__autoreleasing*button, NSString *title, NSInteger idx) {
    NSAssert( button, @"Must not pass nil reference as button" );
    UIButton* localButton = *button;
    if (!localButton) {
      // continue to work on the more convenient localButton, but make sure
      // that the button reference is written to the ivar...
      localButton = *button = [UIButton buttonWithType:UIButtonTypeCustom];
    }
    // other button setup clipped
  };
  // compiler will generate strong stack-allocated temporary variable here
  // to deal with autoreleasing assignment, but make sure ivars are not
  // __block class
  setupButton(&_buttonOne, addressButtonArray[0], 0);
  setupButton(&_buttonTwo, addressButtonArray[1], 1);

  DebugLog(@"%@", _buttonOne);
  [_addressOptionView addSubview:_buttonOne];
  [_addressOptionView addSubview:_buttonTwo];

  // top-most branch was clipped for this example
  return _addressOptionView;
}

Answer 2

这行是问题所在...

button = [[UIButton alloc] init];

完成此操作后，传递给块的按钮引用的副本现在指向内存中的其他位置。 这不会改变其中原始按钮引用指向你在那里复制的按钮引用指向只更改。 请记住，目标-c是价值传递！