UIScrollView contentsize is reset to zero when using auto layout [duplicate]

Question

I'm using autolayout to change the height of my scrollview. I add some subviews to the scrollview where I manually increment the content size. But when I get an event where I am about to change the height the content size is zero.

Here is the code:

-(void) addTag:(NSString *)tagName {

    ...
    [button addTarget:self action:@selector(tagPressed:) forControlEvents:UIControlEventTouchUpInside];
    [self setContentSize:CGSizeMake(self.frame.size.width, self.contentSize.height+60)];
    [self.items addObject: button];
    NSLog(@"content height: %0.2f", self.contentSize.height);


}

Console Output:

 2013-04-18 18:23:06.106 TouchSelectApp[19944:c07] content height: 120.00

Here I output the contentSize :

- (void)tagPressed:(UIButton *)sender {

    NSLog(@"1 content height: %0.2f", self.contentSize.height);
    ...
}

The console shows:

 2013-04-18 18:17:24.747 TouchSelectApp[19944:c07] 1 content height: 0.00

I don't why the content height is set to zero. Help Me!

Update: Here is the problem I am trying to solve.

I am have a scroll view with buttons. Initially it only shows one button. When the button is pressed tagPressed: is called. Tag Pressed changes the height to show all the buttons. Then when the user selects a button the scrollview's height is changed to the original and the offset is set to the button's origin. The below code works but the animation is all wrong. If I change the offset and before the animation block then it just sets the offset to zero.

- (void)tagPressed:(UIButton *)sender {

     CGPoint p;
     float maxHeight = self.items.count * 60;


     if (self.height.constant == maxHeight) {
        self.height.constant = 60;
        p = CGPointMake(0, sender.frame.origin.y-5);     
     }else {
         self.height.constant = maxHeight;
         p = CGPointMake(0, 0);
     }

     [self.superview setNeedsUpdateConstraints];

     [UIView animateWithDuration:0.5f animations: ^{
          [self.superview layoutIfNeeded];
     } completion:^(BOOL finished) {
          [self setContentOffset:p];

     }];

}

Answer 1

If you use auto layout with a UIScrollView, you don't set the contentSize property. See here for more information (scroll down to the section on UIScrollView).