ios 最大长度 UITextField

Max length UITextField

提问by Giorgio Nocera

When I've tried How to you set the maximum number of characters that can be entered into a UITextField using swift?, I saw that if I use all 10 characters, I can't erase the character too.

当我尝试如何使用 swift 设置可以输入到 UITextField 的最大字符数时？，我看到如果我使用所有10个字符，我也无法擦除该字符。

The only thing I can do is to cancel the operation (delete all the characters together).

我唯一能做的就是取消操作（一起删除所有字符）。

Does anyone know how to not block the keyboard (so that I can't add other letters/symbols/numbers, but I can use the backspace)?

有谁知道如何不阻塞键盘（这样我就不能添加其他字母/符号/数字，但我可以使用退格键）？

回答by Imanou Petit

With Swift 5 and iOS 12, try the following implementation of textField(_:shouldChangeCharactersIn:replacementString:)method that is part of the UITextFieldDelegateprotocol:

使用 Swift 5 和 iOS 12，尝试以下textField(_:shouldChangeCharactersIn:replacementString:)方法的实现，这是UITextFieldDelegate协议的一部分：

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    guard let textFieldText = textField.text,
        let rangeOfTextToReplace = Range(range, in: textFieldText) else {
            return false
    }
    let substringToReplace = textFieldText[rangeOfTextToReplace]
    let count = textFieldText.count - substringToReplace.count + string.count
    return count <= 10
}

• The most important part of this code is the conversion from range(NSRange) to rangeOfTextToReplace(Range<String.Index>). See this video tutorialto understand why this conversion is important.
• To make this code work properly, you should also set the textField's smartInsertDeleteTypevalue to UITextSmartInsertDeleteType.no. This will prevent the possible insertion of an (unwanted) extra space when performing a paste operation.

• 这段代码最重要的部分是从range( NSRange) 到rangeOfTextToReplace( Range<String.Index>)的转换。请参阅此视频教程以了解为什么这种转换很重要。
• 为了使此代码正常工作，您还应该将textField的smartInsertDeleteType值设置为UITextSmartInsertDeleteType.no。这将防止在执行粘贴操作时可能插入（不需要的）额外空间。

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The complete sample code below shows how to implement textField(_:shouldChangeCharactersIn:replacementString:)in a UIViewController:

下面的完整示例代码展示了如何textField(_:shouldChangeCharactersIn:replacementString:)在 a 中实现UIViewController：

import UIKit

class ViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet var textField: UITextField! // Link this to a UITextField in Storyboard

    override func viewDidLoad() {
        super.viewDidLoad()

        textField.smartInsertDeleteType = UITextSmartInsertDeleteType.no
        textField.delegate = self
    }

    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        guard let textFieldText = textField.text,
            let rangeOfTextToReplace = Range(range, in: textFieldText) else {
                return false
        }
        let substringToReplace = textFieldText[rangeOfTextToReplace]
        let count = textFieldText.count - substringToReplace.count + string.count
        return count <= 10
    }

}

回答by Martin

I do it like this:

我这样做：

func checkMaxLength(textField: UITextField!, maxLength: Int) {
    if (countElements(textField.text!) > maxLength) {
        textField.deleteBackward()
    }
}

The code works for me. But I work with storyboard. In Storyboard I add an action for the text field in the view controller on editing changed.

该代码对我有用。但我使用故事板。在 Storyboard 中，我在编辑 changed 时为视图控制器中的文本字段添加了一个操作。

回答by Shan Ye

Update for Swift 4

Swift 4 更新

 func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
     guard let text = textField.text else { return true }
     let newLength = text.count + string.count - range.length
     return newLength <= 10
}

回答by Sruit A.Suk

Add More detail from @Martin answer

从@Martin 答案中添加更多详细信息

// linked your button here
@IBAction func mobileTFChanged(sender: AnyObject) {
    checkMaxLength(sender as! UITextField, maxLength: 10)
}

// linked your button here
@IBAction func citizenTFChanged(sender: AnyObject) {
    checkMaxLength(sender as! UITextField, maxLength: 13)
}

func checkMaxLength(textField: UITextField!, maxLength: Int) {
    // swift 1.0
    //if (count(textField.text!) > maxLength) {
    //    textField.deleteBackward()
    //}
    // swift 2.0
    if (textField.text!.characters.count > maxLength) {
        textField.deleteBackward()
    }
}

回答by Sai kumar Reddy

In Swift 4

在斯威夫特 4

10 Characters limit for text field and allow to delete(backspace)

文本字段的 10 个字符限制并允许删除（退格）

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        if textField ==  userNameFTF{
            let char = string.cString(using: String.Encoding.utf8)
            let isBackSpace = strcmp(char, "\b")
            if isBackSpace == -92 {
                return true
            }
            return textField.text!.count <= 9
        }
        return true
    }

回答by Basil Mariano

Swift 3

斯威夫特 3

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

            let nsString = NSString(string: textField.text!)
            let newText = nsString.replacingCharacters(in: range, with: string)
            return  newText.characters.count <= limitCount
    }

回答by Jeremy Andrews

func checkMaxLength(textField: UITextField!, maxLength: Int) {
        if (textField.text!.characters.count > maxLength) {
            textField.deleteBackward()
        }
}

a small change for IOS 9

IOS 9 的一个小改动

回答by mohsen

you can extend UITextField and add an @IBInspectableobject for handle it:

您可以扩展 UITextField 并添加一个@IBInspectable对象来处理它：

SWIFT 5

快速 5

import UIKit
private var __maxLengths = [UITextField: Int]()
extension UITextField {
    @IBInspectable var maxLength: Int {
        get {
            guard let l = __maxLengths[self] else {
                return 150 // (global default-limit. or just, Int.max)
            }
            return l
        }
        set {
            __maxLengths[self] = newValue
            addTarget(self, action: #selector(fix), for: .editingChanged)
        }
    }
    @objc func fix(textField: UITextField) {
        if let t = textField.text {
            textField.text = String(t.prefix(maxLength))
        }
    }
}

and after that define it on attribute inspector

然后在属性检查器上定义它

See Swift 4 original Answer

请参阅Swift 4 原始答案

回答by maxwell

If you want to overwrite the last letter:

如果你想覆盖最后一个字母：

let maxLength = 10

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

    if range.location > maxLength - 1 {
        textField.text?.removeLast()
    }

    return true
}

回答by frouo

I posted a solution using IBInspectable, so you can change the max length value both in interface builder or programmatically. Check it out here

我使用 发布了一个解决方案IBInspectable，因此您可以在界面构建器中或以编程方式更改最大长度值。在这里查看