Question

如果TextField为空，我需要禁用make按钮。否则它会崩溃我的应用

（主题1：致命错误：在解开可选值时意外发现nil ）。

我知道，这里人们写了很多次。但我尝试了StackOverflow的许多例子，如：

if (MyTextField.text?.isEmpty)! {
MyButton.isEnabled = false
MyButton.alpha = 0.5
}

上面的代码我放入了viewDidLoad并且它没有用。如果我按下按钮：

@IBAction func acceptButton(_ sender: Any) {
if (MyTextField.text?.isEmpty)! {
MyButton.isEnabled = false
MyButton.alpha = 0.5
...

然后按钮始终禁用。甚至我在TextField中放了一些数字。

下面的代码也不起作用：

override func viewDidLoad() {
        super.viewDidLoad()
MyTextField.addTarget(self, action: #selector(actionTextFieldIsEditingChanged), for: UIControlEvents.editingChanged)
...
}
...
 @objc func actionTextFieldIsEditingChanged(sender: UITextField) {
        if sender.MyTextField.isEmpty {
            MyButton.isEnabled = false
            MyButton.alpha = 0.5
        } else {
            MyButton.isEnabled = true
            MyButton.alpha = 1.0
        }
 }

我不能使用的其他部分代码，因为它是从2014 - 2015年开始的。

Answer 1

You need to implement UITextFieldDelegate method to enable button when there is text in text filed.

class ViewController: UIViewController { 

   override func viewDidLoad() {
    super.viewDidLoad()

       myTextField.delegate = self
   }

}

Implement this delegate method...

extension ViewController: UITextFieldDelegate { 


  func textFieldDidEndEditing(_ textField: UITextField) {

    if let text = textField.text, text.isEmpty {
        MyButton.isUserInteractionEnabled = false
        MyButton.isEnabled = false
        MyButton.alpha = 0.5
    } else {
       MyButton.isUserInteractionEnabled = true
        MyButton.isEnabled = true
        MyButton.alpha = 1
   }

  }

}

You can disable button in viewDidLoad method as well.

if let text = MyTextField.text, text.isEmpty {
    MyButton.isUserInteractionEnabled = false
    MyButton.isEnabled = false
    MyButton.alpha = 0.5
}

EDIT

You can also enable and disable button as user types in textfield.

extension ViewController: UITextFieldDelegate {  

  func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {

    let text = (textField.text! as NSString).replacingCharacters(in: range, with: string)

    if text.isEmpty{

        MyButton.isUserInteractionEnabled = false
        MyButton.isEnabled = false
        MyButton.alpha = 0.5

    } else {

        MyButton.isUserInteractionEnabled = true
        MyButton.isEnabled = true
        MyButton.alpha = 1
   }

    return true
  }
}

Answer 2

第一组

override func viewDidLoad()
{
    super.viewDidLoad()
    btn.isEnabled = false
}

然后使用文本字段委托方法

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    print(textField.text?.count ?? "default")
    if textField == MyTextField
    {
    if MyTextField.text?.count == 1 && string == ""
            {
                MyButton.isEnabled = false
            }
            else
            {
                MyButton.isEnabled = true
            }
    }
    return true
}

Answer 3

@IBAction func acceptButton(_ sender: Any) {
  if (MyTextField.text?.isEmpty)! {
    print("i am not doing anything")
   }
  else{
      //perform the code
  }
 }

Answer 4

为此使用UITextFieldDelegate方法shouldChangeCharactersIn。

首先将您的课程与UITextFieldDelegate这样绑定

class ClassName: UIViewController, UITextFieldDelegate { ...

然后将此代码添加到您的viewDidLoad

myTextField?.delegate = self
MyButton?.isUserInteractionEnabled = false
MyButton?.alpha = 0.5

并实现此委托方法

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

        let text = (textField.text! as NSString).replacingCharacters(in: range, with: string)

        if !text.isEmpty{
            MyButton?.isUserInteractionEnabled = true
            MyButton?.alpha = 1.0
        } else {
            MyButton?.isUserInteractionEnabled = false
            MyButton?.alpha = 0.5
        }
        return true
    }

Answer 5

我没有看到完整的答案，所以去了：

iOS有一个严格的约定，即变量名和函数名应以小写字母开头。仅类和类型应以大写字母开头。因此，在下面的代码中，我将MyButton更改为myButton，并将MyTextField更改为myTextField。
请勿使用isUserInteractionEnabled和alpha。只需设置按钮的isEnabled标志，然后让UIKit决定如何绘制禁用的按钮即可。这样，您就可以按照正常的HIG约定显示禁用按钮。
如果您的文本字段为空，则向您的viewWillAppear(_:)函数添加代码以禁用该按钮。

赞：

override func viewWillAppear(_ animated: Bool) {
    myButton.isEnabled = (myTextField.text?.count ?? 0) > 0
}

使您的视图控制器符合UITextFieldDelegate协议。然后，将控件从文本字段拖放到视图控制器上，以连接委托链接。
如果文本字段为空，则向视图控制器添加textField(_:shouldChangeCharactersIn:replacementString:)函数以禁用按钮。请注意，此函数必须确定替换完成后文本字段是否为空，因此它需要计算替换字符串后字段文本的长度。您可以将UITextFieldDelegate函数添加到视图控制器的扩展中，以很好地将它们分开。

赞：

extension ViewController: UITextFieldDelegate {
    func textField(_ textField: UITextField, 
      shouldChangeCharactersIn range: NSRange, 
      replacementString string: String) -> Bool {
        //Make sure this method is being called
        guard textField == myTextField else { return true }
        let newLength = (textField.text?.count ?? 0) - range.length + string.count
        myButton.isEnabled = newLength > 0
        return true
    }
}

如果TextField为空，则禁用Button

5 个答案: