Changing/Animating maximumNumberOfLines in UITextView? - ios

Question

I have a UITextView and initially I want to set it to have 4 lines, however when the user clicks a read more button, I want to expand it to full length, I assume this is either through getting maximumNumberOfLines to 0 or to a high number, say 30
Issue is, after changing lines from 4 to 0 (or 30) it doesn't relayout the uitextview to be its full height, it seems capped at 4 lines.
I call self.setNeedsLayout() and self.layoutIfNeeded() to trigger layout, but it won't revert to its full height
I have also tried calling descriptionTextView.invalidateIntrinsicContentSize() after changing the line count with no luck
What am I doing wrong here?
Thanks

Answer 1

You may be doing a couple things wrong...
First, in order to "auto-size" the height of the textView, it must have scrolling disabled.
Second, it cannot have a fixed height (neither a height constraint not top & bottom constraints).
Edit: For clarification... When I say "no bottom constraint" that doesn't mean it cannot have a bottom constraint. Rather, the bottom constraint cannot be set in a way that would prevent the textView's height from changing. So, for example, if the textView is in a table view cell, a bottom constraint is fine, as long as the cell is designed and used in a way that the height of the textView controls (or contributes to) the height of the cell.
This is a simple example that will toggle the textView between 4-lines and Zero-lines (showing all the text content):
class ExpandingTextViewViewController: UIViewController {
let descriptionTextView: UITextView = {
let v = UITextView()
v.translatesAutoresizingMaskIntoConstraints = false
// disable scrolling
v.isScrollEnabled = false
// give it a background color to make it easy to see the frame
v.backgroundColor = .yellow
return v
}()
let theButton: UIButton = {
let v = UIButton()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .red
v.setTitle("Toggle TextView", for: .normal)
return v
}()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(theButton)
view.addSubview(descriptionTextView)
NSLayoutConstraint.activate([
// button 40-pts from the top, centered horizontally
theButton.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 40.0),
theButton.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 0.0),
// textView 40-pts from bottom of button, 20-pts padding left and right
// NO height or bottom constraint
descriptionTextView.topAnchor.constraint(equalTo: theButton.bottomAnchor, constant: 40.0),
descriptionTextView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 20.0),
descriptionTextView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -20.0),
])
// give the textView some sample text
descriptionTextView.text = "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum."
// start with max number of lines set to 4
descriptionTextView.textContainer.maximumNumberOfLines = 4
theButton.addTarget(self, action: #selector(toggleTextView), for: .touchUpInside)
}
#objc func toggleTextView() -> Void {
// toggle max number of lines between 4 and Zero
descriptionTextView.textContainer.maximumNumberOfLines =
(descriptionTextView.textContainer.maximumNumberOfLines == 4) ? 0 : 4
// tell auto-layout abour the change
descriptionTextView.invalidateIntrinsicContentSize()
}
}
Results:
Of course, you'll need to add some code to handle a case where your textView has so much text it will extend beyond the bottom of the screen (or outside the bounds of its superview) -- either by checking the resulting height, adjusting it and toggling scrolling, or embedding the textView in a UIScrollView (for example).

Answer 2

Changing the number of lines on your textField just affects the number of lines your textField is allowed to use to display its text. Setting maximumNumberOfLines to 0 crams the text all on one "line" and truncates it at the end of its width - so it doesn't really hide the remaining text in that sense.
Instead of changing maximumNumberOfLines, you'd be best off letting the text fill the number of lines that is natural for it, and animating the UITextView's heightAnchor instead.