App crash when add some views (ie UIView, UITextView, UIImageView, ...) to main view
import UIKit
class ViewController: UIViewController {
let textview: UITextView = {
let textview2 = UITextView()
textview2.text = "Hello World"
textview2.font = UIFont.boldSystemFont(ofSize: 18)
textview2.textAlignment = .center
return textview2
}()
override func viewDidLoad() {
super.viewDidLoad()
textview.translatesAutoresizingMaskIntoConstraints = false
textview.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
textview.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
view.addSubview(textview)
}
}
How to create views by programmatically?
Edit: I forgot to add the view before setting constraints. So you need to set constraints after adding subviews.
You must set constraints after view.addSubview like this :
import UIKit
class ViewController: UIViewController {
let textview: UITextView = {
let textview2 = UITextView()
textview2.text = "Hello World"
textview2.font = UIFont.boldSystemFont(ofSize: 18)
textview2.textAlignment = .center
return textview2
}()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(textview)
textview.translatesAutoresizingMaskIntoConstraints = false
textview.heightAnchor.constraint(equalToConstant: 100).isActive = true
textview.widthAnchor.constraint(equalToConstant: 200).isActive = true
textview.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
textview.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
}
}
First you need to add view.addSubview(textview) then add constraints.
import UIKit
class testViewController: UIViewController {
let textview: UITextView = {
let textview2 = UITextView()
textview2.text = "Hello World"
textview2.font = UIFont.boldSystemFont(ofSize: 18)
textview2.textAlignment = .center
return textview2
}()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(textview)
textview.translatesAutoresizingMaskIntoConstraints = false
textview.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
textview.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
// you need to specify height and width constraints as well otherwise UITextView will not appear
textview.widthAnchor.constraint(equalToConstant: 100).isActive = true
textview.heightAnchor.constraint(equalToConstant: 30).isActive = true
}
}
You need to add subview first view.addSubview(textview)
before adding constraints and set height and width also for textview as you can see updated code:
import UIKit
class ViewController: UIViewController {
let textview: UITextView = {
let textview2 = UITextView()
textview2.text = "Hello World"
textview2.font = UIFont.boldSystemFont(ofSize: 18)
textview2.textAlignment = .center
return textview2
}()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(textview)
textview.translatesAutoresizingMaskIntoConstraints = false
textview.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
textview.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
textview.widthAnchor.constraint(equalToConstant: 150).isActive = true
textview.heightAnchor.constraint(equalToConstant: 80).isActive = true
}
}
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