Here's my code:
__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
and buttonTwo
is not properties.
After I call addressOptionView getter
, these two buttons are deallocated immediately, thus they don't show up in the view (I guess, nil when NSLog
).
I changed the setupButton
block to @property
and it doesn't work either. Changing two button to @property
doesn't work too.
However, when I change the setupButton
block to
UIButton * (^setupButton)(NSString *, NSInteger)
Two buttons do show up, but I cannot access them later in other methods ( nil
already).
Can somebody give me a brief explanation about what do I do wrong ? How do I make it work ? Thanks.
@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;
}
This line is the problem...
button = [[UIButton alloc] init];
Once you do that, the copy of the reference to your button that you passed into your block is now pointing to a different location in memory. This does not change where the original button reference is pointing as you are only changing where the copied button reference is pointing. Remember, objective-c is pass by value!
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