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

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

- (void)textFieldTextEditingChanged:(UITextField *)field
{
  //不支持系統(tǒng)表情的輸入
  if ([[textField textInputMode] primaryLanguage]==nil||[[[textField textInputMode] primaryLanguage]isEqualToString:@"emoji"]) {
  return;
  }
  //中英文數(shù)字判斷
  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]; // 鍵盤輸入模式
  if ([lang isEqualToString:@"zh-Hans"]) { // 簡(jiǎn)體中文輸入，包括簡(jiǎn)體拼音，健體五筆，簡(jiǎn)體手寫
  UITextRange *selectedRange = [textField markedTextRange];
  //獲取高亮部分
  UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
  // 沒有高亮選擇的字，則對(duì)已輸入的文字進(jìn)行字?jǐn)?shù)統(tǒng)計(jì)和限制
  if (!position) {
   if ([self unicodeLengthOfString:textField.text] > kMaxLength){
   [self saveOKText:textField.text];
   return;
   }
  }
  // 有高亮選擇的字符串，則暫不對(duì)文字進(jìn)行統(tǒng)計(jì)和限制
  else{
  }
  }else{ // 中文輸入法以外的直接對(duì)其統(tǒng)計(jì)限制即可，不考慮其他語種情況
  if ([self unicodeLengthOfString:textField.text] > kMaxLength) {
   [self saveOKText:textField.text];
   return;
  }
  }
}

#pragma mark - 謂詞條件限制
/**
 pattern中,輸入需要驗(yàn)證的通過的字符
 小寫a-z
 大寫A-Z
 漢字\u4E00-\u9FA5
 數(shù)字\u0030-\u0039
 @param str 要過濾的字符
 @return YES 只允許輸入字母和漢字
 */
- (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;//超出的字符數(shù)
 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;