我仍在学习Swift,并且正在尝试创建扩展以将占位符添加到UITextView。
我的想法是创建2个UITextViews,其中一个以文本作为占位符,当用户开始编辑文本时,它实际上是隐藏的,用户正在修改另一个UITextView。
但是,我的问题不是要在UITextView中使用占位符,而是要考虑如何使用扩展来解决此问题。
我的问题是,我必须在实现中进行哪些更改才能创建从调用方看来是:myTextView.placeholder("a placeholder text..")
到目前为止,我已经在UIViewController中创建了它,需要将其移动到扩展中,但是我有很多存储的属性,因此无法使用。
这是我的代码:
import UIKit
class ViewController: UIViewController, UITextViewDelegate {
let myTextView: UITextView = {
let textView = UITextView()
textView.tag = 0
textView.backgroundColor = UIColor.yellow
textView.layer.cornerRadius = 8
textView.translatesAutoresizingMaskIntoConstraints = false
return textView
}()
let textViewPlaceHolder: UITextView = {
let textViewPlaceHolder = UITextView()
textViewPlaceHolder.tag = 1
textViewPlaceHolder.text = "Placeholder text.."
textViewPlaceHolder.textColor = UIColor.lightGray
textViewPlaceHolder.backgroundColor = UIColor.clear
textViewPlaceHolder.translatesAutoresizingMaskIntoConstraints = false
return textViewPlaceHolder
}()
func textViewDidChange(_ textView: UITextView) {
myTextView.becomeFirstResponder()
if textView.tag == 1 && (myTextView.text != nil || myTextView.text != "") {
textView.isHidden = true
textViewPlaceHolder.resignFirstResponder()
} else if textView.tag == 0 {
if myTextView.text == nil || myTextView.text == "" {
textViewPlaceHolder.becomeFirstResponder()
myTextView.resignFirstResponder()
textViewPlaceHolder.isHidden = false
textViewPlaceHolder.text = "Placeholder text.."
}
}
}
func textViewDidBeginEditing(_ textView: UITextView) {
DispatchQueue.main.async {
self.textViewPlaceHolder.selectedRange = NSMakeRange(0, 0)
}
}
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor.lightGray
view.addSubview(myTextView)
textViewConstraints()
view.addSubview(textViewPlaceHolder)
myTextViewPHConstraints()
myTextView.delegate = self
textViewPlaceHolder.delegate = self
}
func textViewConstraints() {
myTextView.widthAnchor.constraint(equalTo: self.view.widthAnchor, constant: -16).isActive = true
myTextView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
myTextView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor).isActive = true
myTextView.heightAnchor.constraint(equalToConstant: 200).isActive = true
}
func myTextViewPHConstraints() {
textViewPlaceHolder.widthAnchor.constraint(equalTo: self.view.widthAnchor, constant: -16).isActive = true
textViewPlaceHolder.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
textViewPlaceHolder.centerYAnchor.constraint(equalTo: self.view.centerYAnchor).isActive = true
textViewPlaceHolder.heightAnchor.constraint(equalToConstant: 200).isActive = true
}
}
正如我上面提到的,我仍然在学习Swift,这个问题不是要解决一个非常具体的问题,而不仅仅是解决这个问题,它意味着要学习如何解决Swift扩展中的问题。
注意:不要使用上面的代码来解决占位符问题,因为它不能完美地工作。
最佳答案
您可以执行以下操作:
extension UITextView {
private struct AssociatedKeys {
static var placeholder = "placeholder"
}
var placeholder: String! {
get {
guard let placeholder = objc_getAssociatedObject(self, &AssociatedKeys.placeholder) as? String else {
return String()
}
return placeholder
}
set(value) {
objc_setAssociatedObject(self, &AssociatedKeys.placeholder, value, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
}
关于ios - 具有存储属性的扩展,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/44113732/