ios - 如何使用 Swift 根据 UITextView 文本长度启用和禁用 Alertaction 按钮

Question

我正在 UIAlertController 和两个按钮中实现 UITextView。在这里，我需要使用 Swift 验证基于 AlertviewController 按钮 Done 的 Textview empty 启用和禁用。

带有 TextView 的 AlertView

@IBAction func alertAction(_ sender: Any) {

        let alert = UIAlertController(title: "Hello Alert!", message: "Write Your Text and Informations\n\n\n\n\n", preferredStyle: .alert)
        alert.view.autoresizesSubviews = true

        textView = UITextView(frame: CGRect.zero)
        textView.translatesAutoresizingMaskIntoConstraints = false
        textView.backgroundColor = UIColor.clear
        textView.delegate = self
        textView.text = "Placeholder text goes right here..."
        textView.textColor = UIColor.lightGray

        let leadConstraint = NSLayoutConstraint(item: alert.view, attribute: .leading, relatedBy: .equal, toItem: textView, attribute: .leading, multiplier: 1.0, constant: -8.0)
        let trailConstraint = NSLayoutConstraint(item: alert.view, attribute: .trailing, relatedBy: .equal, toItem: textView, attribute: .trailing, multiplier: 1.0, constant: 8.0)

        let topConstraint = NSLayoutConstraint(item: alert.view, attribute: .top, relatedBy: .equal, toItem: textView, attribute: .top, multiplier: 1.0, constant: -64.0)
        let bottomConstraint = NSLayoutConstraint(item: alert.view, attribute: .bottom, relatedBy: .equal, toItem: textView, attribute: .bottom, multiplier: 1.0, constant: 64.0)
        alert.view.addSubview(textView)
        NSLayoutConstraint.activate([leadConstraint, trailConstraint, topConstraint, bottomConstraint])

        alert.addAction(UIAlertAction(title: "Cancel", style: .default, handler: { action in

        }))

        alert.addAction(UIAlertAction(title: "Done", style: .default, handler: { action in
            print("\(String(describing: self.textView.text))")
        }))
        present(alert, animated: true)
    }

    func textViewDidBeginEditing(_ textView: UITextView) {
        if textView.textColor == UIColor.lightGray {
            textView.text = ""
            textView.textColor = UIColor.black
        }
    }

    func textViewDidEndEditing(_ textView: UITextView) {

        if textView.text == "" {
            textView.text = "Placeholder text ..."
            textView.textColor = UIColor.lightGray
        }
    }

Answer 1

UIAlertController 可以已经包含 UITextFields。您可以根据 textField 是否为空来管理 UIAlertAction 的 isEnabled 状态。

1. 在您的 ViewController 中为 UIAlertAction 创建属性。

var doneAction: UIAlertAction?

2. 在 alertAction 按钮事件上，添加 textField、cancelAction 和 doneAction 在上面创建的 alert 中。

@IBAction func alertAction(_ sender: Any) {
    let alert = UIAlertController(title: "Hello Alert!", message: "Write Your Text and Informations\n\n\n\n\n", preferredStyle: .alert)
    alert.view.autoresizesSubviews = true

    //TextField...
    let textView = UITextView(frame: CGRect.zero)
    textView.translatesAutoresizingMaskIntoConstraints = false
    textView.backgroundColor = UIColor.clear
    textView.delegate = self
    textView.textColor = UIColor.lightGray
    textView.text = "Placeholder text goes right here..."

    let leadConstraint = NSLayoutConstraint(item: alert.view, attribute: .leading, relatedBy: .equal, toItem: textView, attribute: .leading, multiplier: 1.0, constant: -8.0)
    let trailConstraint = NSLayoutConstraint(item: alert.view, attribute: .trailing, relatedBy: .equal, toItem: textView, attribute: .trailing, multiplier: 1.0, constant: 8.0)

    let topConstraint = NSLayoutConstraint(item: alert.view, attribute: .top, relatedBy: .equal, toItem: textView, attribute: .top, multiplier: 1.0, constant: -64.0)
    let bottomConstraint = NSLayoutConstraint(item: alert.view, attribute: .bottom, relatedBy: .equal, toItem: textView, attribute: .bottom, multiplier: 1.0, constant: 64.0)
    alert.view.addSubview(textView)
    NSLayoutConstraint.activate([leadConstraint, trailConstraint, topConstraint, bottomConstraint])

    //Done action...
    let doneAction = UIAlertAction(title: "Done", style: .default) { (action) in
        print("\(String(describing: alert.textFields?.first?.text))")
    }
    doneAction.isEnabled = false
    alert.addAction(doneAction)
    self.doneAction = doneAction

    //Cancel action...
    alert.addAction(UIAlertAction(title: "Cancel", style: .default, handler: nil))

    self.present(alert, animated: true)
}

3. 现在，覆盖 UITextViewDelegate 的 textView(_:, shouldChangeTextIn:replacementText:) 方法，

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    let text = (textView.text! as NSString).replacingCharacters(in: range, with: text)
    self.doneAction?.isEnabled = !text.isEmpty && text != "Placeholder text goes right here..."
    textView.textColor = (!text.isEmpty && text != "Placeholder text goes right here...") ? .black : .lightGray
    return true
}

func textViewDidBeginEditing(_ textView: UITextView) {
    textView.text = nil
}