Question

我正在向UITextField添加UIAlertController，其显示为AlertView。在驳回UIAlertController之前，我想验证UITextField的输入。基于验证，我想要忽略UIAlertController。但我不知道如何在按下按钮时阻止UIAlertController的解雇操作。有没有人解决这个问题或任何想法从哪里开始？我去谷歌但没有运气：/谢谢！

Answer 1

您已更正：如果用户可以点按提醒中的按钮，则系统会将其解除警报。所以你想阻止用户点击按钮！这只是禁用UIAlertAction按钮的问题。如果禁用了提醒操作，则用户无法点击提醒操作。

要将其与文本字段验证相结合，请使用文本字段委托方法或操作方法（在创建时在文本字段的配置处理程序中配置），以根据文本的具体情况适当启用/禁用UIAlertActions（或者还没有输入。

这是一个例子。我们创建了这样的文本字段：

alert.addTextFieldWithConfigurationHandler {
    (tf:UITextField!) in
    tf.addTarget(self, action: "textChanged:", forControlEvents: .EditingChanged)
}

我们有一个取消操作和一个OK操作，我们将OK操作带入禁用的世界：

(alert.actions[1] as UIAlertAction).enabled = false

随后，除非文本字段中有实际文字，否则用户无法点击确定：

func textChanged(sender:AnyObject) {
    let tf = sender as UITextField
    var resp : UIResponder = tf
    while !(resp is UIAlertController) { resp = resp.nextResponder() }
    let alert = resp as UIAlertController
    (alert.actions[1] as UIAlertAction).enabled = (tf.text != "")
}

编辑以上代码的当前版本（Swift 3.0.1及更高版本）：

alert.addTextField { tf in
    tf.addTarget(self, action: #selector(self.textChanged), for: .editingChanged)
}

和

alert.actions[1].isEnabled = false

和

@objc func textChanged(_ sender: Any) {
    let tf = sender as! UITextField
    var resp : UIResponder! = tf
    while !(resp is UIAlertController) { resp = resp.next }
    let alert = resp as! UIAlertController
    alert.actions[1].isEnabled = (tf.text != "")
}

Answer 2

我已经简化了亚马的答案，而没有观察层次结构。这将把动作本身作为一个弱变量。这是一个完全有效的例子：

weak var actionToEnable : UIAlertAction?

func showAlert()
{
    let titleStr = "title"
    let messageStr = "message"

    let alert = UIAlertController(title: titleStr, message: messageStr, preferredStyle: UIAlertControllerStyle.Alert)

    let placeholderStr =  "placeholder"

    alert.addTextFieldWithConfigurationHandler({(textField: UITextField) in
        textField.placeholder = placeholderStr
        textField.addTarget(self, action: "textChanged:", forControlEvents: .EditingChanged)
    })

    let cancel = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.Cancel, handler: { (_) -> Void in

    })

    let action = UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: { (_) -> Void in
        let textfield = alert.textFields!.first!

        //Do what you want with the textfield!
    })

    alert.addAction(cancel)
    alert.addAction(action)

    self.actionToEnable = action
    action.enabled = false
    self.presentViewController(alert, animated: true, completion: nil)
}

func textChanged(sender:UITextField) {
    self.actionToEnable?.enabled = (sender.text! == "Validation")
}

Answer 3

克服@Matt的答案，这里是我在Obj-C中做同样事情的方式

- (BOOL)textField: (UITextField*) textField shouldChangeCharactersInRange: (NSRange) range replacementString: (NSString*)string
{
    NSString *newString = [textField.text stringByReplacingCharactersInRange: range withString: string];

    // check string length
    NSInteger newLength = [newString length];
    BOOL okToChange = (newLength <= 16);    // don't allow names longer than this

    if (okToChange)
    {
        // Find our Ok button
        UIResponder *responder = textField;
        Class uiacClass = [UIAlertController class];
        while (![responder isKindOfClass: uiacClass])
        {
            responder = [responder nextResponder];
        }
        UIAlertController *alert = (UIAlertController*) responder;
        UIAlertAction *okAction  = [alert.actions objectAtIndex: 0];

        // Dis/enable Ok button based on same-name
        BOOL duplicateName = NO;
        // <check for duplicates, here>

        okAction.enabled = !duplicateName;
    }


    return (okToChange);
}

Answer 4

我意识到这是在Objectiv-C中，但它显示了主体。稍后我会用swift版本更新它。

您也可以使用块作为目标。

向ViewController添加一个属性，以便该块（swift的闭包）具有强大的引用

@property (strong, nonatomic) id textValidationBlock;

然后像这样创建AlertViewController：

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Title" message:@"Message" preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {

}];

   __weak typeof(self) weakSelf = self;
UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"Ok" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
        [weakSelf doSomething];

}];
[alertController addAction:cancelAction];
[alertController addAction:okAction];
[alertController.actions lastObject].enabled = NO;
self.textValidationBlock = [^{
    UITextField *textField = [alertController.textFields firstObject];
    if (something) {
        alertController.message = @"Warning message";
        [alertController.actions lastObject].enabled = NO;
    } else if (somethingElse) {
        alertController.message = @"Another warning message";
        [alertController.actions lastObject].enabled = NO;
    } else {
        //Validation passed
        alertController.message = @"";
        [alertController.actions lastObject].enabled = YES;
    }

} copy];
[alertController addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {
    textField.placeholder = @"placeholder here";
    [textField addTarget:weakSelf.textValidationBlock action:@selector(invoke) forControlEvents:UIControlEventEditingChanged];
}];
[self presentViewController:alertController animated:YES completion:nil];

Answer 5

这与其他答案中的想法相同，但是我希望在扩展名中隔离一个简单的方法，并可以在任何UIViewController子类中使用。它显示一个带有一个文本输入字段和两个按钮的警报：“确定”和“取消”。

extension UIViewController {

    func askForTextAndConfirmWithAlert(title: String, placeholder: String, okHandler: @escaping (String?)->Void) {
        
        let alertController = UIAlertController(title: title, message: nil, preferredStyle: .alert)
        
        let textChangeHandler = TextFieldTextChangeHandler { text in
            alertController.actions.first?.isEnabled = !(text ?? "").isEmpty
        }
        
        var textHandlerKey = 0
        objc_setAssociatedObject(self, &textHandlerKey, textChangeHandler, .OBJC_ASSOCIATION_RETAIN)

        alertController.addTextField { textField in
            textField.placeholder = placeholder
            textField.clearButtonMode = .whileEditing
            textField.borderStyle = .none
            textField.addTarget(textChangeHandler, action: #selector(TextFieldTextChangeHandler.onTextChanged(sender:)), for: .editingChanged)
        }

        let okAction = UIAlertAction(title: CommonLocStr.ok, style: .default, handler: { _ in
            guard let text = alertController.textFields?.first?.text else {
                return
            }
            okHandler(text)
            objc_setAssociatedObject(self, &textHandlerKey, nil, .OBJC_ASSOCIATION_RETAIN)
        })
        okAction.isEnabled = false
        alertController.addAction(okAction)

        alertController.addAction(UIAlertAction(title: CommonLocStr.cancel, style: .cancel, handler: { _ in
            objc_setAssociatedObject(self, &textHandlerKey, nil, .OBJC_ASSOCIATION_RETAIN)
        }))

        present(alertController, animated: true, completion: nil)
    }

}

class TextFieldTextChangeHandler {
    
    let handler: (String?)->Void
    
    init(handler: @escaping (String?)->Void) {
        self.handler = handler
    }

    @objc func onTextChanged(sender: AnyObject) {
        handler((sender as? UITextField)?.text)
    }
}

防止解雇UIAlertController

5 个答案: