Question

I have a scrollview. I add a button to this scrollview and release it after.

UIButton * saveButton = [UIButton buttonWithType:UIButtonTypeCustom];
saveButton.frame = CGRectMake(415.0, 473, 80, 38);
saveButton.titleLabel.font = [UIFont fontWithName:@"Heiti TC" size:24];
[saveButton setTitle:@"" forState:UIControlStateNormal];
[saveButton setContentEdgeInsets:UIEdgeInsetsMake(2, 0, 0, 0)];
saveButton.backgroundColor = [UIColor clearColor];
[saveButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal ];
[saveButton setBackgroundImage:[UIImage imageNamed:@"save.png"] forState:UIControlStateNormal];
[saveButton addTarget:self action:@selector(save) forControlEvents:UIControlEventTouchUpInside];
saveButton.hidden = NO;
[self.scrollview addSubview:saveButton];
[saveButton release];

The application crashes when the view appears on screen, and I try and touch any part of the screen.

If I comment out

[saveButton release];

the application works perfectly.

I thought the retain count of the button would be incremented once I add it to the scrollview so it would be safe for me to release the button.

What’s going on here? Is adding something to a scrollview not the same as adding it to the main view like below?

[self.view addSubview:saveButton];

Answer 1

buttonWithType: is a convenience constructor, so it already creates an autoreleased instance, and there is no need to release the object.

That means the following line of code is an error:

[saveButton release];

You should not send release, as the instance is already autoreleased.

Check the UIButton reference for details.