Swift insert big height label into view - ios

Question

I'm new to the Swift and trying to add label programmatically to UIView which is embedded into scroll view.
Actually, i want to have something with header (picture and title for half of the screen) and content below (text with unknown length and images).
I'm added a view container and depending on content i want to add label or image view.
Most of the time it will be like that:
text
image
text
image
and so on.
Add label code (Swift 4):
let label = UILabel()
label.numberOfLines = 0
label.text = blogItem.text
containerView.addSubview(label)
label.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint(item: label, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem: containerView, attribute: NSLayoutAttribute.top, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: label, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: containerView, attribute: NSLayoutAttribute.leading, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: label, attribute: NSLayoutAttribute.trailing, relatedBy: NSLayoutRelation.equal, toItem: containerView, attribute: NSLayoutAttribute.trailing, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: label, attribute: NSLayoutAttribute.bottom, relatedBy: NSLayoutRelation.equal, toItem: containerView, attribute: NSLayoutAttribute.bottom, multiplier: 1, constant: 0).isActive = true
The problem is that text is truncated, when comes to the end of the screen and no scrolling at all.
How can i add bottom constraint correctly (i believe that's all happens because of it?) to make expected behaviour?

Answer 1

Make sure you created a proper hierarchy for working UIScrollView:
Add a scrollView to the hierarchy and use autolayout to properly layout it, e.g., if it is supposed to cover the whole view of the viewController:
scrollView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
scrollView.leftAnchor.constraint(equalTo: self.view.leftAnchor),
scrollView.rightAnchor.constraint(equalTo: self.view.rightAnchor),
scrollView.topAnchor.constraint(equalTo: self.view.topAnchor),
scrollView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
])
Then you need to add a contentView to the scrollView and provide a proper layout constraints for it, so if you want vertically scrollable scrollView in the example I started above, you need following autolayout constraints:
contentView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
// horizontal anchors of contentView are constrained to scrollView superview
// to prevent it from scrolling horizontally
contentView.leftAnchor.constraint(equalTo: self.view.leftAnchor),
contentView.rightAnchor.constraint(equalTo: self.view.rightAnchor),
// but vertical anchors of contentView are constrained to
// scrollView to allow scrolling
contentView.topAnchor.constraint(equalTo: scrollView.topAnchor),
contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor),
])
Notice here that I constrained the leftAnchor and rightAnchor of the contentView to the self.view rather than to scrollView to make it of fixed width. However, top and bottom anchors are constrained to the scrollView, so they are expanded and scrollable when contentView needs more space.
Now you add to the contentView all the content that you want, and you lay it out using autolayout as if the contentView was a view with infinite height - scrollView will take care of presenting it whole by scrolling. So in my example if the only content would be one huge UILabel with many lines (label is a subview of contentView):
label.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
label.leftAnchor.constraint(equalTo: contentView.leftAnchor),
label.rightAnchor.constraint(equalTo: contentView.rightAnchor),
label.topAnchor.constraint(equalTo: contentView.topAnchor),
label.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
])
Try to go over your code and check your constraints. It might be that you miss constraints in both cases, and the fact that it works in first case is just a coincidence.