Swift视图没有显示出来

Question

I'm trying to create a UITextView on my main view, I managed to do it with textView = UITextView(frame: CGRect(x: 10, y: 10, width: 300, height: 300)) however, I can't do it with constraints for some reasons. Here's my function that I call in viewDidLoad() :

private func configureTextView() {
        view.addSubview(textView)
        textView.topAnchor.constraint(equalTo: view.topAnchor, constant: 10)
        textView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 10)
        textView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -10)
        textView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -10)
        textView.backgroundColor = .red
        print(view.subviews)
}

And here's the textView :

private let textView: UITextView = {
        let view = UITextView()
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
}()

I'm still a very beginner, but print(view.subviews) shows that textView is a subview of the main view (I guess)

[<UITextView: 0x7fdf64809600; frame = (0 0; 0 0); text = '';
clipsToBounds = YES; gestureRecognizers = <NSArray: 0x60000062f450>;
layer = <CALayer: 0x60000083b360>; contentOffset: {0, 0}; contentSize:
{0, -8}; adjustedContentInset: {0, 0, 0, 0}>]

Answer 1

You create constraints, but never set them as active. Changing to this should help make it display properly:

textView.topAnchor.constraint(equalTo: view.topAnchor, constant: 10).isActive = true
textView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 10).isActive = true
textView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -10).isActive = true
textView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -10).isActive = true

Answer 2

You can also use "SnapKit"

https://github.com/SnapKit/SnapKit

pod 'SnapKit', '~> 5.0.0'

    self.addSubView(textView)
    textView.snp.makeConstraints { (make) -> Void in
           make.top.equalTo(0)
           make.bottom.equalTo(0)
           make.left.equalTo(0)
           make.right.equalTo(0)
    }