How to contain overflowed UILabel's text inside UIView?

Solution 1:

Here are my thoughts on what I think is happening.

I will start with the padding bit. I believe both these cases are actually the same:

The default behaviour is to center the text and in both cases this is happening. In the second case (image on the right) which you say there is a padding, the UILabel cannot fit another line of text at that font size and so it stops at line 4 and centers the text with the label's frame.

If you increase the label height to 500 for example, you will see that it is not a random padding, but rather a centering.

Here is a simple approximation of how many lines of text a given height might support.

let label = UILabel()
label.text = "This is my text.This is my text.This is my text.This is my text.This is my text.This is my text.This is my text."
label.numberOfLines = 0
label.sizeToFit()

// I added these line
print("Max lines that will fit: \(floor(100.0 / label.font.lineHeight))")
print("Max lines that will fit: \(floor(130.0 / label.font.lineHeight))")

The answer printed out is 4.0 and 6.0. As I increased your label height to 130 as follows, and it gave me 6 lines as approximated:

// Inside your set up function
container.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
    container.leadingAnchor.constraint(equalTo: view.leadingAnchor),
    container.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
    container.heightAnchor.constraint(equalToConstant: 130.0),
    container.widthAnchor.constraint(equalToConstant: 100.0)
])

let label = UILabel()
label.text = "This is my text.This is my text.This is my text.This is my text.This is my text.This is my text.This is my text."
label.numberOfLines = 0
label.sizeToFit()

So I hope that explains the bit about the padding.

Now coming to how to prevent the overflow, I think your autolayout already prevents that. I think also adding clipsToBounds on the container will prevent the label from overflowing.

Finally, aligning the label to the top is a different question altogether. However there was a wonderful solution I came across here which was subclassing a UILabel and overriding drawRect like so:

// Credit to Ma11hew28 https://stackoverflow.com/a/41367948/1619193
class TopAlignedLabel: UILabel {
  override func drawText(in rect: CGRect) {
    let textRect = super.textRect(forBounds: bounds, limitedToNumberOfLines: numberOfLines)
    super.drawText(in: textRect)
  }
}

// Your new set up function will be like this, I have commented
// the 2 changes I made
private func setup() {
    let container = UIView()
    container.backgroundColor = .red
    view.addSubview(container)
    
    container.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        container.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
        container.heightAnchor.constraint(equalToConstant: 100.0),
        container.widthAnchor.constraint(equalToConstant: 100.0)
    ])
    
    // Use top aligned label
    let label = TopAlignedLabel()
    label.text = "This is my text."
    label.numberOfLines = 0
    label.sizeToFit()
    
    container.addSubview(label)
    
    label.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        label.widthAnchor.constraint(equalTo: container.widthAnchor)
    ])
    
    // Clip container to bounds to prevent overflow
    container.clipsToBounds = true
}

Final version prevents overflow and aligns text to the top when there is less text: