UIButton does not scroll when adding to UIScrollView - ios

Question

I have added a UIButton, and a UILabel to a UIScrollView. I added two constraints to the button using Auto Layout, and none to the label. I can see label moving on the screen, however I do not see the button moving. I figure this has something to do with the Auto Layout constraints I added to the button. I would like to see to the button scroll the same way I see the label scrolling around on the window / screen.
Below is how I set everything up:
_welcomeScroller = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height)];
_welcomeScroller.userInteractionEnabled = YES;
_welcomeScroller.scrollEnabled = YES;
_welcomeScroller.showsHorizontalScrollIndicator = YES;
_welcomeScroller.showsVerticalScrollIndicator = YES;
#ifdef DEBUG
[_welcomeScroller setBackgroundColor:[UIColor greenColor]];
#endif
[self.view addSubview:_welcomeScroller];
CGSize welcomeScrollerSize = CGSizeMake(2000, 2000);
[_welcomeScroller setContentSize:welcomeScrollerSize];
// add test label
_test = [[UILabel alloc] initWithFrame:CGRectMake(200, 200, 200, 200)];
[_test setText:#"TEST"];
[_test setFont:[UIFont systemFontOfSize:44]];
[_test setBackgroundColor:[UIColor redColor]];
[_welcomeScroller addSubview:_test];
// add about btn to lower right
_welcomeAbout = [UIButton buttonWithType:UIButtonTypeInfoDark];
[_welcomeAbout addTarget:self action:#selector(showAboutScreen:) forControlEvents:UIControlEventTouchUpInside];
[_welcomeAbout setTranslatesAutoresizingMaskIntoConstraints:NO];
[_welcomeScroller addSubview:_welcomeAbout];
NSLayoutConstraint *pullToBottom = [NSLayoutConstraint constraintWithItem:_welcomeAbout attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:_welcomeScroller.superview attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-10.0];
NSLayoutConstraint *pullToRight = [NSLayoutConstraint constraintWithItem:_welcomeAbout attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:_welcomeScroller.superview attribute:NSLayoutAttributeRight multiplier:1.0 constant:-10];
[_welcomeScroller.superview addConstraints:#[pullToBottom, pullToRight]];

Answer 1

From Apple's technical note:
In general, Auto Layout considers the top, left, bottom, and right
edges of a view to be the visible edges. That is, if you pin a view to
the left edge of its superview, you’re really pinning it to the
minimum x-value of the superview’s bounds. Changing the bounds origin
of the superview does not change the position of the view.
The UIScrollView class scrolls its content by changing the origin of
its bounds. To make this work with Auto Layout, the top, left, bottom,
and right edges within a scroll view now mean the edges of its content
view.
The button isn't scrolling because constraints are set relative to the visible left edge of the scrollview.
Apple's solution suggests:
Create a plain UIView content view for your scroll view that will be
the size you want your content to have. Make it a subview of the
scroll view but let it continue to translate the autoresizing mask
into constraints.
Inside this content view, you can use constraints as you would normally.