iOS中对文本的字符限制示例详解

[textfield addTarget:self action:@selector(textFieldTextEditingChanged:) forControlEvents:UIControlEventEditingChanged];

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

- (void)textFieldTextEditingChanged:(UITextField *)field
{
  //不支持系统表情的输入
  if ([[textField textInputMode] primaryLanguage]==nil||[[[textField textInputMode] primaryLanguage]isEqualToString:@"emoji"]) {
  return;
  }
  //中英文数字判断
  NSString *strig =[[NSString alloc]initWithString:textField.text];
  [strig enumerateSubstringsInRange:NSMakeRange(0, strig.length) options:NSStringEnumerationByComposedCharacterSequences usingBlock:^(NSString * _Nullable substring, NSRange substringRange, NSRange enclosingRange, BOOL * _Nonnull stop) {
  if (substring.length >=2) {
   textField.text =[textField.text stringByReplacingOccurrencesOfString:substring withString:@""];
  }
  }];
  
  NSString *toBeString = textField.text;
  NSString *lastString;
  if(toBeString.length>0){
  lastString=[toBeString substringFromIndex:toBeString.length-1];
  if ([self isInputRuleAndNumber:lastString] != YES) {
   textField.text = [toBeString substringToIndex:toBeString.length-1];
  }
  }
  if (textField.text.length == 0) {
  return;
  }
  NSString *lang = [textField.textInputMode primaryLanguage]; // 键盘输入模式
  if ([lang isEqualToString:@"zh-Hans"]) { // 简体中文输入，包括简体拼音，健体五笔，简体手写
  UITextRange *selectedRange = [textField markedTextRange];
  //获取高亮部分
  UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
  // 没有高亮选择的字，则对已输入的文字进行字数统计和限制
  if (!position) {
   if ([self unicodeLengthOfString:textField.text] > kMaxLength){
   [self saveOKText:textField.text];
   return;
   }
  }
  // 有高亮选择的字符串，则暂不对文字进行统计和限制
  else{
  }
  }else{ // 中文输入法以外的直接对其统计限制即可，不考虑其他语种情况
  if ([self unicodeLengthOfString:textField.text] > kMaxLength) {
   [self saveOKText:textField.text];
   return;
  }
  }
}

#pragma mark - 谓词条件限制
/**
 pattern中,输入需要验证的通过的字符
 小写a-z
 大写A-Z
 汉字\u4E00-\u9FA5
 数字\u0030-\u0039
 @param str 要过滤的字符
 @return YES 只允许输入字母和汉字
 */
- (BOOL)isInputRuleAndNumber:(NSString *)str {
 NSString *pattern = @"[a-zA-Z\u4E00-\u9FA5\\u0030-\\u0039]";
 NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", pattern];
 BOOL isMatch = [pred evaluateWithObject:str];
 return isMatch;
}

-(NSUInteger)unicodeLengthOfString:(NSString *) text {
 NSUInteger asciiLength = 0;
 for (NSUInteger i = 0; i < text.length; i++) {
 unichar uc = [text characterAtIndex: i];
 asciiLength += isascii(uc) ? 1 : 2;
 }
 return asciiLength;
}

- (void )saveOKText:(NSString *)textStr
{
 int overLength = (int)[self unicodeLengthOfString:textStr] - kMaxLength;//超出的字符数
 if (overLength <= 0 ){
 _field.text = textStr;
 return;
 }
 NSString *lastStr = [textStr substringFromIndex:textStr.length-1];
 
 if ([self unicodeLengthOfString:lastStr] >= 2) {
 textStr = [textStr substringToIndex:textStr.length-1];
 NSLog(@"%@",textStr);
 if (overLength >0) {
  NSLog(@"%@",textStr);
  [self saveOKText:textStr];
 }else{
  _field.text = textStr;
  return;
 }
 }else if ([self unicodeLengthOfString:lastStr] == 1) {
 textStr = [textStr substringToIndex:textStr.length-1];
 if (overLength >0) {
  [self saveOKText:textStr];
 }else{
  _field.text = textStr;
  return;
 }
 }
}

unichar uc = [text characterAtIndex: i];
asciiLength += isascii(uc) ? 1 : 2;