限制UITextview的行数

Question

我想知道如何限制用户在编辑 UITextField 时可以输入的行数（不是其他问题中询问的字符数）。

理想情况下，我想将输入限制为最大值。 10 行。

我需要从哪里开始？我是否用某种方法来做到这一点？在

 - (BOOL)textViewShouldBeginEditing:(UITextView *)aTextView

Answer 1

Maciek Czarnik 的回答对我来说不起作用，但它让我了解了该怎么做。

iOS 7+

Swift

textView.textContainer.maximumNumberOfLines = 10
textView.textContainer.lineBreakMode = .byTruncatingTail

ObjC

textView.textContainer.maximumNumberOfLines = 10;
textView.textContainer.lineBreakMode = NSLineBreakByTruncatingTail;

Answer 2

也许这可以帮助（iOS 7+）：

textView.textContainer.maximumNumberOfLines = 10;
[textView.layoutManager textContainerChangedGeometry:textView.textContainer];

我猜即使是第一行也应该能达到目的，但没有......也许它是 SDK 中的一个错误

Answer 3

你的想法是对的，但方法是错误的。每当文本要更改时，就会调用 textView:shouldChangeTextInRange:replacementText: ；您可以使用其 text 属性访问文本视图的当前内容，并且可以使用 [textView.text stringByReplacingCharactersInRange:range withString:replacementText 从传递的范围和替换文本构造新内容]。然后，您可以计算行数并返回“是”以允许更改，或返回“否”以拒绝更改。

Answer 4

在 Swift 3.0 版本中：

self.textView.textContainer.maximumNumberOfLines = self.textViewNumberOflines
self.textView.textContainer.lineBreakMode = .byTruncatingTail

Answer 5

Maciek Czarnik 的答案似乎对我不起作用，即使在 iOS7 中也是如此。它给了我奇怪的行为，我不知道为什么。

我限制 UITextView 中行数的方法很简单：（

仅在 iOS7 中测试）在以下 UITextViewDelegate 方法中：

- (void)textViewDidChange:(UITextView *)textView
{
    NSUInteger maxNumberOfLines = 5;
    NSUInteger numLines = textView.contentSize.height/textView.font.lineHeight;
    if (numLines > maxNumberOfLines)
    {
        textView.text = [textView.text substringToIndex:textView.text.length - 1];
    }
}

Answer 6

这是 Swift 4.2 / Swift 5 中 Numereyes 答案的改进版本，

我做了一些扩展，以便可以重用代码。
我正在使用 While 循环来检查尺寸是否合适。当用户一次粘贴大量文本时，这也适用。

extension UITextView {        
    var numberOfCurrentlyDisplayedLines: Int {
        let size = systemLayoutSizeFitting(UIView.layoutFittingCompressedSize)
        //for Swift <=4.0, replace with next line:
        //let size = systemLayoutSizeFitting(UILayoutFittingCompressedSize)

        return Int(((size.height - layoutMargins.top - layoutMargins.bottom) / font!.lineHeight))
    }

    /// Removes last characters until the given max. number of lines is reached
    func removeTextUntilSatisfying(maxNumberOfLines: Int) {
        while numberOfCurrentlyDisplayedLines > (maxNumberOfLines) {
            text = String(text.dropLast())
            layoutIfNeeded()
        }
    }
}

// Use it in UITextView's delegate method:
func textViewDidChange(_ textView: UITextView) {        
    textView.removeTextUntilSatisfying(maxNumberOfLines: 10)
}        

Answer 7

Swift 4

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    let existingLines = textView.text.components(separatedBy: CharacterSet.newlines)
    let newLines = text.components(separatedBy: CharacterSet.newlines)
    let linesAfterChange = existingLines.count + newLines.count - 1
    return linesAfterChange <= textView.textContainer.maximumNumberOfLines
}

如果您还想限制字符：

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        let existingLines = textView.text.components(separatedBy: CharacterSet.newlines)
        let newLines = text.components(separatedBy: CharacterSet.newlines)
        let linesAfterChange = existingLines.count + newLines.count - 1
        if(text == "\n") {
            return linesAfterChange <= textView.textContainer.maximumNumberOfLines
        }

        let newText = (textView.text as NSString).replacingCharacters(in: range, with: text)
        let numberOfChars = newText.count
        return numberOfChars <= 30 // 30 characters limit
    }
}

不要忘记在 viewDidLoad 中添加您希望限制的行数：

txtView.textContainer.maximumNumberOfLines = 2

Answer 8

给出的其他解决方案不能解决与最后创建的最后一行（问题案例中的第 11 行）相关的问题。

这是一个使用 Swift 4.0 和 Swift 4.0 的可行解决方案。 Xcode 9.0 beta（位于 这篇博文）

   class ViewController: UIViewController, UITextViewDelegate {

      @IBOutlet weak var textView: UITextView!

    override func viewDidLoad() {
        super.viewDidLoad()
        textView.delegate = self
        textView.textContainer.maximumNumberOfLines = 10
        textView.textContainer.lineBreakMode = .byWordWrapping
      }

    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {

        let existingLines = textView.text.components(separatedBy: CharacterSet.newlines)
        let newLines = text.components(separatedBy: CharacterSet.newlines)
        let linesAfterChange = existingLines.count + newLines.count - 1

        return linesAfterChange <= textView.textContainer.maximumNumberOfLines
    }

注意：此解决方案无法处理最后一行太长而无法显示的情况（文本将隐藏在 UITextView 的最右侧）。

Answer 9

Swift 5.7、iOS 16

在 UITextView（或 UITextField）的 UIViewRepresentable 包装器中

func makeUIView(context: Context) -> UITextView {

    let textView = UITextView() // ..or MyCustomUITextView()

    // ..your existing makeUIView body here..

    // Limit to N = 3 visible (displayed) lines.
    textView.textContainer.maximumNumberOfLines = 3

    // When visible line count is exceeded typing can continue,
    // but what's entered will be truncated so hidden from view.
    textView.textContainer.lineBreakMode = .byTruncatingTail

    // ..or prevent further text entry when limit is hit.
    // See https://developer.apple.com/documentation/uikit/nslinebreakmode
    //textView.textContainer.lineBreakMode = .byClipping

    // Set delegate now that other changes are made.
    textView.delegate = self

    return textView
}

Answer 10

与其他答案类似，但可以直接从情节提要使用，无需子类化：

extension UITextView {
    @IBInspectable var maxNumberOfLines: NSInteger {
        set {
            textContainer.maximumNumberOfLines = maxNumberOfLines
        }
        get {
            return textContainer.maximumNumberOfLines
        }
    }
    @IBInspectable var lineBreakByTruncatingTail: Bool {
        set {
            if lineBreakByTruncatingTail {
                textContainer.lineBreakMode = .byTruncatingTail
            }
        }
        get {
            return textContainer.lineBreakMode == .byTruncatingTail
        }
    }
}

Answer 11

请参阅 APPLE 文档：计算文本行数 https ://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/TextLayout/Tasks/CountLines.html

    - (void)textViewDidChangeSelection:(UITextView *)textView{
NSLayoutManager *layoutManager = [textView layoutManager];
unsigned numberOfLines, index, numberOfGlyphs =
(unsigned)[layoutManager numberOfGlyphs];
NSRange lineRange;
for (numberOfLines = 0, index = 0; index < numberOfGlyphs; numberOfLines++){
    (void) [layoutManager lineFragmentRectForGlyphAtIndex:index
            effectiveRange:&lineRange];
    index = (unsigned)NSMaxRange(lineRange);
}
if(numberOfLines > 10){
    self.textField.text = self.lastString;
}

}

处理“\n”

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
if([text containsString:@"\n"]){
    NSLayoutManager *layoutManager = [textView layoutManager];
    unsigned numberOfLines, index, numberOfGlyphs =
            (unsigned)[layoutManager numberOfGlyphs];
    NSRange lineRange;
    for (numberOfLines = 0, index = 0; index < numberOfGlyphs; numberOfLines++){
        (void) [layoutManager lineFragmentRectForGlyphAtIndex:index
                effectiveRange:&lineRange];
        index = (unsigned)NSMaxRange(lineRange);
    }
    NSLog(@"lines = %d",numberOfLines);
    if(numberOfLines >= 10){
        return NO;
    }
}
self.lastString = textView.text;

return YES;

}