限制uitextView或uitextField中粘贴的字符串长度

我可以通过遵循uitextViewDelegate协议中的textViewDidChange:方法来限制输入和粘贴的文本。

- (void)textViewDidChange:(UITextView *)textView
{
    if (textView.text.length >= 10)
    {
        textView.text = [textView.text substringToIndex:10];
    }
}

但我仍然认为这是一种丑陋的黑客行为,苹果似乎应该提供uitextfields和uitextviews的某种“maxlength”属性。

如果有人知道更好的解决方案,请告诉我。

以我刚刚实施委托方法的经验:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

可用于粘贴。整个粘贴的字符串出现在replacementstring:参数中。只需检查它的长度,如果它比您的最大长度长,那么只需从这个委托方法返回no。这不会导致粘贴任何内容。或者,您可以像前面建议的答案那样对其进行子串,但如果太长(如果这是您想要的),则这可以完全防止粘贴。

在textViewDidChange中插入文本后更改文本:如果用户在粘贴后按“撤消”,则会导致应用程序崩溃。

我玩了很久,终于找到了一个可行的解决方案。基本上,逻辑是,如果总长度大于最大字符数,则不允许粘贴,检测溢出的数量并仅插入部分字符串。

使用此解决方案,粘贴板和撤消管理器将按预期工作。

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {
    NSInteger newLength = textView.text.length - range.length + text.length;

    if (newLength > MAX_LENGTH) {
        NSInteger overflow = newLength - MAX_LENGTH;

        dispatch_async(dispatch_get_main_queue(), ^{
            UITextPosition *start = [textView positionFromPosition:nil offset:range.location];
            UITextPosition *end = [textView positionFromPosition:nil offset:NSMaxRange(range)];
            UITextRange *textRange = [textView textRangeFromPosition:start toPosition:end];
            [textView replaceRange:textRange withText:[text substringToIndex:text.length - overflow]];
        });
        return NO;
    }
    return YES;
}

上面链接到的第一个问题中的一个答案应该有效,即使用类似于

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(limitTextField:) name:@"UITextFieldTextDidChangeNotification" object:myTextField];

监视uitextfield中文本的更改并在适当时缩短它。

另外,字符串长度(如'[string length]'中的字符串长度)是一回事,但通常需要在特定编码中将其截断为字节数。我需要将输入和粘贴到uitextview中的操作截断为最大utf8计数,下面是我的操作方法。(对读者来说,为uitextfield做类似的事情是一项练习。)

nsstring+trunceutf8.h

#import <Foundation/Foundation.h>
@interface NSString (TruncateUTF8)
- (NSString *)stringTruncatedToMaxUTF8ByteCount:(NSUInteger)maxCount;
@end

nsstring+trunceutf8.m

#import "NSString+TruncateUTF8.h"
@implementation NSString (TruncateUTF8)
- (NSString *)stringTruncatedToMaxUTF8ByteCount:(NSUInteger)maxCount {
  NSRange truncatedRange = (NSRange){0, MIN(maxCount, self.length)};
  NSInteger byteCount;

  // subtract from this range to account for the difference between NSString's
  // length and the string byte count in utf8 encoding
  do {
    NSString *truncatedText = [self substringWithRange:truncatedRange];
    byteCount = [truncatedText lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
    if (byteCount > maxCount) {
      // what do we subtract from the length to account for this excess count?
      // not the count itself, because the length isn't in bytes but utf16 units
      // one of which might correspond to 4 utf8 bytes (i think)
      NSUInteger excess = byteCount - maxCount;
      truncatedRange.length -= ceil(excess / 4.0);
      continue;
    }
  } while (byteCount > maxCount);

  // subtract more from this range so it ends at a grapheme cluster boundary
  for (; truncatedRange.length > 0; truncatedRange.length -= 1) {
    NSRange revisedRange = [self rangeOfComposedCharacterSequencesForRange:truncatedRange];
    if (revisedRange.length == truncatedRange.length)
      break;
  }

  return (truncatedRange.length < self.length) ? [self substringWithRange:truncatedRange] : self;
}
@end

// tested using:
//    NSString *utf8TestString = @"Hello world, Καλημέρα κόσμε, コンニチハ ∀x∈ℝ ıntəˈnæʃənəl ⌷←⍳→⍴∆∇⊃‾⍎⍕⌈ STARGΛ̊TE γνωρίζω გთხოვთ Зарегистрируйтесь ๏ แผ่นดินฮั่นเสื่อมโทรมแสนสังเวช ሰማይ አይታረስ ንጉሥ አይከሰስ። ᚻᛖ ᚳᚹᚫᚦ ᚦᚫᛏ ᚻᛖ ᛒᚢᛞᛖ ⡌⠁⠧⠑ ⠼⠁⠒  ⡍⠜⠇⠑⠹⠰⠎ ⡣⠕⠌ ░░▒▒▓▓██ ▁▂▃▄▅▆▇█";
//    NSString *truncatedString;
//    NSUInteger byteCount = [utf8TestString lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
//    NSLog(@"length %d: %p %@", (int)byteCount, utf8TestString, utf8TestString);
//    for (; byteCount > 0; --byteCount) {
//        truncatedString = [utf8TestString stringTruncatedToMaxUTF8ByteCount:byteCount];
//        NSLog(@"truncate to length %d: %p %@ (%d)", (int)byteCount, truncatedString, truncatedString, (int)[truncatedString lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);
//    }

我的视图控制器.m

#import "NSString+TruncateUTF8.h"
...
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)replacementText
{
  NSMutableString *newText = textView.text.mutableCopy;
  [newText replaceCharactersInRange:range withString:replacementText];

  // if making string larger then potentially reject
  NSUInteger replacementTextLength = replacementText.length;
  if (self.maxByteCount > 0 && replacementTextLength > range.length) {
    // reject if too long and adding just 1 character
    if (replacementTextLength == 1 && [newText lengthOfBytesUsingEncoding:NSUTF8StringEncoding] > self.maxByteCount) {
      return NO;
    }

    // if adding multiple charaters, ie. pasting, don't reject altogether but instead return YES
    // to accept and truncate immediately after, see http://stackoverflow.com/a/23155325/592739
    if (replacementTextLength > 1) {
      NSString *truncatedText = [newText stringTruncatedToMaxUTF8ByteCount:self.maxByteCount]; // returns same string if truncation needed
      if (truncatedText != newText) {
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0LL), dispatch_get_main_queue(), ^{
          UITextPosition *replaceStart = [textView positionFromPosition:textView.beginningOfDocument offset:range.location];
          UITextRange *textRange = [textView textRangeFromPosition:replaceStart toPosition:textView.endOfDocument];
          [textView replaceRange:textRange withText:[truncatedText substringFromIndex:range.location]];

          self.rowDescriptor.value = (truncatedText.length > 0) ? truncatedText : nil;
        });
      }
    }
  }

  [self updatedFieldWithString:(newText.length > 0) ? newText : nil]; // my method
  return YES;
}

如果你检查一下 string.length 在里面 shouldChangeCharactersIn range: 委托方法

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    if string.length > 1 {
        //pasted string
        // do you stuff like trim
    } else {
        //typed string
    }
    return true
}

此代码不允许用户输入超过maxcharacters的字符。 如果粘贴的文本超过此限制,则“粘贴”命令将不起任何作用。

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    let newText = (textView.text as NSString).replacingCharacters(in: range, with: text)
    return newText.count <= maxCharacters;
}

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{

  if(string.length>10){
    return NO;
  }
  return YES;
}