如何实现占位符文本在 UITextField 中逐字符消失

Question

你能帮帮我吗

在 UITextField 中，当我们提供占位符文本时，当我们输入任何字符时，其占位符字符串将消失。我怎样才能实现只输入的字符而不是完整的字符串？这意味着如果我输入 3 个字符，只有占位符的前 3 个字符会消失。

#编辑 1

另外，新输入的字符文字颜色会发生变化，其余字符文字颜色保持不变。

提前致谢。

Answer 1

否如果在 UITextfield 上创建自定义层后，您将无法执行此操作，您需要检查输入的字符是否与占位符字符串匹配，然后只会替换该字符。另见

Answer 2

我的解决方案是使用 UITextField 文本属性

+(BOOL)shouldChangeCharactersInRange:(NSRange)range
                   replacementString:(NSString *)string
                           textField:(UITextField *)textField
                                mask:(NSString *)mask withMaskTemplate:(NSString *)maskTemplate{

    NSString * alreadyExistString = @"";
    if (string.length == 0) {
        alreadyExistString = textField.text;
        for (int i = range.location; i >= 0; i--) {
            unichar  currentCharMask = [maskTemplate characterAtIndex:i];
            unichar  currentChar = [alreadyExistString characterAtIndex:i];
            if (currentCharMask == currentChar) {// fixed value and _
                continue;
            }else{
                alreadyExistString = [alreadyExistString stringByReplacingCharactersInRange:NSMakeRange(i, 1) withString:@"_"];
                break;
            }
        }
        textField.text = alreadyExistString;
        return NO;
    }else{
        alreadyExistString = [textField.text stringByReplacingCharactersInRange:NSMakeRange(range.location, 1) withString:string];
    }

    NSMutableString * validText = [[NSMutableString alloc] init];

    int last = 0;
    BOOL append = NO;
    for (int i = 0; i < alreadyExistString.length; i++) {
        unichar  currentCharMask = [mask characterAtIndex:i];
        unichar  currentChar = [alreadyExistString characterAtIndex:i];
        BOOL isLetter = [[NSCharacterSet alphanumericCharacterSet] characterIsMember: currentChar];
        BOOL isDigit  = [[NSCharacterSet decimalDigitCharacterSet] characterIsMember: currentChar];
        if ((isLetter && currentCharMask == '#') || (isDigit && currentCharMask == '9')) {
            [validText appendString:[NSString stringWithFormat:@"%c",currentChar]];
        }else{
            if (currentCharMask == '#' || currentCharMask == '9') {
                break;
            }
            if ((isLetter && currentCharMask!= currentChar)|| (isDigit && currentCharMask!= currentChar)) {
                append = YES;
            }
            [validText appendString:[NSString stringWithFormat:@"%c",currentCharMask]];
        }
        last = i;
    }

    for (int i = last+1; i < mask.length; i++) {
        unichar currentCharMask = [mask characterAtIndex:i];
        if (currentCharMask != '#' && currentCharMask != '9') {
            [validText appendString:[NSString stringWithFormat:@"%c",currentCharMask]];
        }
        if (currentCharMask == '#' || currentCharMask == '9') {
            break;
        }
    }
    if (append) {
        [validText appendString:string];
    }

    NSString *placeHolderMask = textField.text;
    NSString *sub = [validText substringWithRange:NSMakeRange(range.location, 1)];
    placeHolderMask = [placeHolderMask stringByReplacingCharactersInRange:NSMakeRange(range.location, 1) withString:sub];
    textField.text = placeHolderMask;
    return NO;
}

@property (nonatomic,strong) NSString * maskTemplate;// like: _2_-__-__A
@property (nonatomic,strong) NSString * mask;// like: #2#-99-##A

最初将文本字段文本设置为屏蔽模板
然后当用户输入时调用 shouldChangeCharactersInRange 并且它做得很好

#编辑 1 我还实现了一些代码，将光标移动到下划线位置。如果有人需要帮助。请评论我会帮助你

#编辑2

我在使用此方法时遇到的问题

无法更改单个文本颜色。对于像@"_" 下划线这样的字符串和具有相同颜色的输入字符，颜色将相同。
如果用户未提供任何输入，那么我必须提供支票以将空白作为字符串发送。
跟踪个人输入。

谢谢，仍在等待是否有任何其他使用占位符字符串的解决方法。

Answer 3

不使用占位符文本，而是在文本字段下方使用 UILabel 并为两者提供相同的字体样式。标签文字应该是像“- - - - -”

并且当用户开始在文本字段上输入时，在每个字符按下后给出一个 space。

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

    if textField.text?.characters.count == 0 && string.characters.count != 0 {
        textField.text = textField.text! + " "
    }
     else {
        return false
    }

    if textField.text?.characters.count == 1 && string.characters.count != 0 {
        textField.text = textField.text! + " "
    }
    else {
        return false
    }

    if textField.text?.characters.count == 2 && string.characters.count != 0 {
        textField.text = textField.text! + " "
    }
    else {
        return false
    }
    if textField.text?.characters.count == 3 && string.characters.count != 0 {
        textField.text = textField.text! + " "
    }
    else {
        return false
    }

    return true
}

Answer 4

对于这种情况，请使用 swift 中的属性字符串，如下所示，

let attributeFontSaySomething : [String : Any] = [NSFontAttributeName : UIFont.systemFont(ofSize: 12.0)]
let attributeColorSaySomething : [String : Any] = [NSForegroundColorAttributeName : UIColor.blue]

var attributes = attributeFontSaySomething
for (key, value) in attributeColorSaySomething {
    attributes(value, forKey: key)
}

let attStringSaySomething = NSAttributedString(string: "Say something", attributes: attributes)

Answer 5

我想这正是您要找的。使用文本 _2_-__-__A（不是占位符文本）创建 UITextField 对象。然后，将其视图控制器用作委托，并将其添加到视图控制器：

-(BOOL)textField:(UITextField*)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString*)string{
    if (range.length>1) return NO; // Avoids removing multiple characters at once
    if (range.location==1) range.location++;  // '2' index
    if (range.location==3) range.location++;  // '-' index
    if (range.location==6) range.location++;  // '-' index
    if (range.location==9)  return NO; // 'A' index
    if (range.location==10) return NO; // String end
    if ([string isEqualToString:@""]) return NO; //Avoids removing characters

    if (range.length==0) {
        range.length++;
        UITextPosition *beginning = textField.beginningOfDocument;
        UITextPosition *start = [textField positionFromPosition:beginning offset:range.location];
        UITextPosition *end = [textField positionFromPosition:start offset:range.length];
        UITextRange *textRange = [textField textRangeFromPosition:start toPosition:end];
        [textField setSelectedTextRange:textRange];
    }

    return YES;
}
-(void)textFieldDidBeginEditing:(UITextField*)textField{
    UITextPosition *beginning = textField.beginningOfDocument;
    UITextPosition *start = [textField positionFromPosition:beginning offset:0];
    UITextPosition *end = [textField positionFromPosition:start offset:0];
    UITextRange *textRange = [textField textRangeFromPosition:start toPosition:end];
    [textField setSelectedTextRange:textRange];
}
-(BOOL)textFieldShouldReturn:(UITextField*)textField{
    [passwordInput resignFirstResponder];
    return YES;
}

它应该按预期工作。

Answer 6

我不认为占位符的默认行为是可编辑的，但您可以使用 NSAttributedString 模拟占位符值来完成您想要完成的工作。

我确定这可以优化，但我在这里创建了一个处理程序 class 作为给定 UITextField 的委托，操纵用户输入的字符串以实现所需影响。您使用所需的占位符字符串初始化处理程序，因此您可以使任何文本字段以这种方式工作。

import UIKit

class CustomPlaceholderTextFieldHandler: NSObject {
    let placeholderText: String
    let placeholderAttributes = [NSForegroundColorAttributeName : UIColor.lightGray]
    let inputAttributes = [NSForegroundColorAttributeName : UIColor(red: 255/255, green: 153/255, blue: 0, alpha: 1.0)]
    var input = ""

    init(placeholder: String) {
        self.placeholderText = placeholder
        super.init()
    }

    func resetPlaceholder(for textField: UITextField) {
        input = ""
        setCombinedText(for: textField)
    }

    fileprivate func setCursorPosition(for textField: UITextField) {
        guard let cursorPosition = textField.position(from: textField.beginningOfDocument, offset: input.characters.count)
            else { return }

        textField.selectedTextRange = textField.textRange(from: cursorPosition, to: cursorPosition)
    }

    fileprivate func setCombinedText(for textField: UITextField) {
        let placeholderSubstring = placeholderText.substring(from: input.endIndex)
        let attributedString = NSMutableAttributedString(string: input + placeholderSubstring, attributes: placeholderAttributes)
        attributedString.addAttributes(inputAttributes, range: NSMakeRange(0, input.characters.count))
        textField.attributedText = attributedString
    }
}

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

        if string == "" {
            if input.characters.count > 0 {
                input = input.substring(to: input.index(before: input.endIndex))
            }
        } else {
            input += string
        }

        if input.characters.count <= placeholderText.characters.count {
            setCombinedText(for: textField)
            setCursorPosition(for: textField)
            return false
        }
        return true
    }

    func textFieldDidBeginEditing(_ textField: UITextField) {
        setCursorPosition(for: textField)
    }
}

以上是我初始化 gif 的方法：

class ViewController: UIViewController {

    @IBOutlet weak var textField: UITextField!
    let placeholderHandler = CustomPlaceholderTextFieldHandler(placeholder: "_2_-__-__A")

    override func viewDidLoad() {
        super.viewDidLoad()
        textField.delegate = placeholderHandler
        placeholderHandler.resetPlaceholder(for: textField)
    }
}

这可以扩展为在初始化时获取颜色参数、字体等，或者您可能会发现 subclass UITextField 并使其成为自己的委托更清晰。我还没有真正测试过 selecting/deleting/replacing 多个字符。

input 变量将 return 用户在任何给定点输入的文本。此外，使用固定宽度的字体会消除用户键入时的抖动并替换占位符文本。

如何实现占位符文本在 UITextField 中逐字符消失

How to achieve that placeholder text disappears character by character in UITextField

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