UITextView doesn't display all of the text on small screens when using exclusions

I have a UITextView:

var textView: UITextView = {
    let textView = UITextView()
    textView.textColor = .orange
    textView.isScrollEnabled = false
    textView.isEditable = false
    return textView
}()

I have it constrained to another view, which is in turn part of a UIStackView

    mainStack.axis = .vertical
    mainStack.addArrangedSubview(titleView)
    mainStack.addArrangedSubview(bodyView)
    
    titleView.addSubview(textView)
    textView.translatesAutoresizingMaskIntoConstraints = false
    
    let padding: CGFloat = 5
    
    NSLayoutConstraint.activate([
        textView.leadingAnchor.constraint(equalTo: titleView.leadingAnchor, constant: padding),
        textView.trailingAnchor.constraint(equalTo: titleView.trailingAnchor, constant: -padding),
        textView.topAnchor.constraint(equalTo:  titleView.topAnchor, constant: padding),
        textView.bottomAnchor.constraint(equalTo: titleView.bottomAnchor, constant: -padding)
    ])

In addition I have a button constrained partially in the same area

let mainActionButton = UIButton()
titleView.addSubview(mainActionButton)
        
mainActionButton.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            mainActionButton.trailingAnchor.constraint(equalTo: titleView.trailingAnchor),
            mainActionButton.topAnchor.constraint(equalTo:  titleView.topAnchor),
            mainActionButton.heightAnchor.constraint(equalTo: mainActionButton.widthAnchor)
        ])

At runtime, after viewDidLoad is called, I use the following to make sure the text flows around the button

    textView.textContainer.exclusionPaths = [UIBezierPath(rect: mainActionButton.frame)]
    self.layoutSubviews()

Generally, this works nicely, as you can see from the screenshot:

However, when I changed the padding to anything less than 4 in the constraints for the uitextview, on small screens only, it does not display the last line, as you can see below:

Again, this doesn't happen if:

• There is no exclusion path (button)
• It is on a large screen
• The padding is more than 3 px

Does anyone have any idea why this might be happening?

While I'm not 100% sure why this was happening, I think it's because I had placed the UITextView in a stackview that was also in a scrollview, and therefore it was never getting any hard definition of a content size.

What I did was create a method that is called after the view is loaded, which calculates the intrinsic content size of a label that would be in the same location using 'systemLayoutSizeFitting' (and of course subtracting any extra padding / width'). I took that height value and set a hard constraint. For some reason, I had to add 30 to make it work properly - there must be some other aspect of the textfield that adds 30 px of padding.

func layoutTitle() {
let label = UILabel()
label.font = Fonts.titleFont
label.numberOfLines = -1
label.text = titleTextView.text
let size = CGSize(width: self.frame.width - (padding * 2) - mainActionButton.frame.width, height: 0)
let newSize = label.systemLayoutSizeFitting(size, withHorizontalFittingPriority: .required, verticalFittingPriority: .fittingSizeLevel)
var height = newSize.height + 30
titleTextView.heightAnchor.constraint(greaterThanOrEqualToConstant: height).isActive = true
}

NOTE I'm adding a minimum reproducible example below; you should be able to pop this into the view controller file of a single view app. The tricky part is that different lengths of string work on different phones, but if you run the iPhone 14 Pro Max simulator, you'll see that only up to the number 16 appears, hiding 17, 18, and 19. If you then add '20' to the titleTextView's text, it appears again.

import UIKit
class ViewController: UIViewController {
let primaryView = PrimaryView()
override func viewDidLoad() {
super.viewDidLoad()
self.view.constrain(primaryView)
}
override func viewDidLayoutSubviews() {
primaryView.layoutTitle()
}
}
class PrimaryView: UIView {
var viewController: UIViewController!
var mainScroll = UIScrollView()
var mainStack: UIStackView = {
let stackView = UIStackView()
stackView.axis = .vertical
return stackView
} ()
var titleTextView: UITextView = {
let textView = UITextView()
textView.font = UIFont.systemFont(ofSize: 36)
textView.isScrollEnabled = false
textView.isEditable = false
return textView
}()
var mainActionButtonArea = UIView()
var mainActionButton: UIButton = {
let button = UIButton()
button.setImage(UIImage(systemName: "square.and.pencil.circle.fill", withConfiguration: UIImage.SymbolConfiguration(pointSize: 36)), for: .normal)
return button
}()
var bodyView = UIStackView()
init() {
super.init(frame: .zero)
setUpMainStack()
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setUpMainStack() {
// Constrain scrollview to view
self.constrain(mainScroll, padding: 30)
// Constrain UIStackView to scroll view
mainScroll.constrain(mainStack)
mainScroll.widthAnchor.constraint(equalTo: mainStack.widthAnchor).isActive = true
// Add child views
mainStack.addArrangedSubview(titleTextView)
mainStack.addArrangedSubview(bodyView)
titleTextView.text = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19"
// Add action button area + action button
mainScroll.constrain(mainActionButtonArea, except: [.leading, .bottom])
mainActionButtonArea.constrain(mainActionButton, padding: 10)
mainActionButton.heightAnchor.constraint(equalTo: mainActionButton.widthAnchor).isActive = true
}
func layoutTitle() {
// This adds the exception path; needs to be called after subviews are already laid out
let buttonPath = UIBezierPath(rect: mainActionButtonArea.frame)
titleTextView.textContainer.exclusionPaths = [buttonPath]
}
}
// Helper function
extension UIView {
enum ConstraintType: CaseIterable { case leading, trailing, top, bottom }
func constrain(_ child: UIView, padding: CGFloat = 0, except: [ConstraintType] = []) {
self.addSubview(child)
child.translatesAutoresizingMaskIntoConstraints = false
for type in ConstraintType.allCases where !except.contains(type) {
switch type {
case .leading:
child.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: padding).isActive = true
case .trailing:
child.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: -padding).isActive = true
case .top:
child.topAnchor.constraint(equalTo: self.topAnchor, constant: padding).isActive = true
case .bottom:
child.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: -padding).isActive = true
}
}
}
}

Based on your "minimum reproducible example" ...

I've found in the past that when setting .exclusionPaths in a UITextView, the layout needs to be "prompted" to update. It also seems much more reliable to set the .text after setting the exclusion paths.

Also - while not related to what's going on here - I find it very helpful during development to give UI elements contrasting background colors to make it easy to see the framing at run-time.

So, here is your example, almost as-is, with these changes:

• constrained PrimaryView to the safe-area
• gave bodyView a height, and added a label as a subview to identify it
• gave all the views background colors

your "helper" function - unmodified

// Helper function
extension UIView {
enum ConstraintType: CaseIterable { case leading, trailing, top, bottom }
func constrain(_ child: UIView, padding: CGFloat = 0, except: [ConstraintType] = []) {
self.addSubview(child)
child.translatesAutoresizingMaskIntoConstraints = false
for type in ConstraintType.allCases where !except.contains(type) {
switch type {
case .leading:
child.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: padding).isActive = true
case .trailing:
child.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: -padding).isActive = true
case .top:
child.topAnchor.constraint(equalTo: self.topAnchor, constant: padding).isActive = true
case .bottom:
child.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: -padding).isActive = true
}
}
}
}

view controller class - modified to respect safe-area

class ExclusionTestViewController: UIViewController {
let primaryView = MyPrimaryView()
override func viewDidLoad() {
super.viewDidLoad()
//self.view.constrain(primaryView)
primaryView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(primaryView)
let g = view.safeAreaLayoutGuide
NSLayoutConstraint.activate([
primaryView.topAnchor.constraint(equalTo: g.topAnchor, constant: 0.0),
primaryView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 0.0),
primaryView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: 0.0),
primaryView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: 0.0),
])
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
primaryView.layoutTitle()
}
}

PrimaryView class - original, except added colors and bodyView properties

class MyPrimaryView: UIView {
var mainScroll = UIScrollView()
var mainStack: UIStackView = {
let stackView = UIStackView()
stackView.axis = .vertical
return stackView
} ()
var titleTextView: UITextView = {
let textView = UITextView()
textView.font = UIFont.systemFont(ofSize: 36)
textView.isScrollEnabled = false
textView.isEditable = false
return textView
}()
var mainActionButtonArea = UIView()
var mainActionButton: UIButton = {
let button = UIButton()
button.setImage(UIImage(systemName: "square.and.pencil.circle.fill", withConfiguration: UIImage.SymbolConfiguration(pointSize: 36)), for: .normal)
return button
}()
var bodyView = UIStackView()
init() {
super.init(frame: .zero)
setUpMainStack()
// set background colors to make it easy to see framing
self.backgroundColor = .cyan
mainScroll.backgroundColor = .systemBlue
mainStack.backgroundColor = .systemYellow
titleTextView.backgroundColor = .green
mainActionButtonArea.backgroundColor = .red.withAlphaComponent(0.75)
mainActionButton.backgroundColor = .white
bodyView.backgroundColor = UIColor(white: 0.95, alpha: 1.0)
// let's give the bodyView a height constraint of 180
bodyView.heightAnchor.constraint(equalToConstant: 180.0).isActive = true
// and add a label to identify it
let v = UILabel()
v.font = .italicSystemFont(ofSize: 24.0)
v.text = "Body View"
bodyView.constrain(v, padding: 12.0, except: [.trailing, .bottom])
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setUpMainStack() {
// Constrain scrollview to view
self.constrain(mainScroll, padding: 30)
// Constrain UIStackView to scroll view
mainScroll.constrain(mainStack)
mainScroll.widthAnchor.constraint(equalTo: mainStack.widthAnchor).isActive = true
// Add child views
mainStack.addArrangedSubview(titleTextView)
mainStack.addArrangedSubview(bodyView)
titleTextView.text = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19"
// Add action button area + action button
mainScroll.constrain(mainActionButtonArea, except: [.leading, .bottom])
mainActionButtonArea.constrain(mainActionButton, padding: 10)
mainActionButton.heightAnchor.constraint(equalTo: mainActionButton.widthAnchor).isActive = true
}
func layoutTitle() {
// This adds the exception path; needs to be called after subviews are already laid out
let buttonPath = UIBezierPath(rect: mainActionButtonArea.frame)
titleTextView.textContainer.exclusionPaths = [buttonPath]
}
}

and it looks like this:

As you pointed out, the "17 18 19" line is missing.

So, let's force the text view to update its layout when we set the exclusion path. The only change will be a few lines added here:

func layoutTitle() {
// This adds the exception path; needs to be called after subviews are already laid out
let buttonPath = UIBezierPath(rect: mainActionButtonArea.frame)
titleTextView.textContainer.exclusionPaths = [buttonPath]
// "re-set" the text view's text and force a layout pass
let str: String = titleTextView.text ?? ""
titleTextView.text = ""
titleTextView.text = str
titleTextView.setNeedsLayout()
titleTextView.layoutIfNeeded()
}

Now when we run it, we get:

and there's no need to create a temporary label with sizing calculations that may, or may not, be reliable and flexible.

As a side note, to get this to "play well" with dynamic size changes - such as device rotation - it's still got a bit of work to do.