文章結構

1.UITextField字數限制
2.UITextView字數限制

一、UITextField字數限制

[_textFieldInput addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
_lableLimit.text = [NSString stringWithFormat:@"0/%lu",_limitLength];

#pragma mark - 字數限制
- (void)textFieldDidChange:(UITextField *)textField
{
    NSInteger kMaxLength = _limitLength;
    NSString *toBeString = textField.text;
    NSString *lang = [[UIApplication sharedApplication]textInputMode].primaryLanguage; //ios7之前使用[UITextInputMode currentInputMode].primaryLanguage
    if ([lang isEqualToString:@"zh-Hans"]) { //中文輸入
        UITextRange *selectedRange = [textField markedTextRange];
        //獲取高亮部分
        UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
        if (!position) {// 沒有高亮選擇的字，則對已輸入的文字進行字數統計和限制
            if (toBeString.length > kMaxLength) {
                textField.text = [toBeString substringToIndex:kMaxLength];
            }
        }
        else{//有高亮選擇的字符串，則暫不對文字進行統計和限制
        }
    }else{//中文輸入法以外的直接對其統計限制即可，不考慮其他語種情況
        if (toBeString.length > kMaxLength) {
            textField.text = [toBeString substringToIndex:kMaxLength];
        }
    }
    
     _lableLimit.text = [NSString stringWithFormat:@"%lu/%lu",textField.text.length,_limitLength];
}

二、UITextView字數限制與剩余字數顯示

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
    //不支持系統表情的輸入
    if ([[textView textInputMode] primaryLanguage] == nil||[[[textView textInputMode] primaryLanguage]isEqualToString:@"emoji"]) {
        return NO;
    }
    UITextRange *selectedRange = [textView markedTextRange];
    //獲取高亮部分
    UITextPosition *pos = [textView positionFromPosition:selectedRange.start offset:0];
    //獲取高亮部分內容
    //NSString * selectedtext = [textView textInRange:selectedRange];
    //如果有高亮且當前字數開始位置小于最大限制時允許輸入
    if (selectedRange && pos) {
        NSInteger startOffset = [textView offsetFromPosition:textView.beginningOfDocument toPosition:selectedRange.start];
        NSInteger endOffset = [textView offsetFromPosition:textView.beginningOfDocument toPosition:selectedRange.end];
        NSRange offsetRange = NSMakeRange(startOffset, endOffset - startOffset);
        if (offsetRange.location < MAX_LIMIT_NUMS) {
            return YES;
        }else{
            return NO;
        }
    }
    NSString *comcatstr = [textView.text stringByReplacingCharactersInRange:range withString:text];
    NSInteger caninputlen = MAX_LIMIT_NUMS - comcatstr.length;
    if (caninputlen >=0){
        return YES;
    }else{
        NSInteger len = text.length + caninputlen;
        //防止當text.length + caninputlen < 0時，使得rg.length為一個非法最大正數出錯
        NSRange rg = {0,MAX(len,0)};
        if (rg.length >0){
            NSString *s =@"";
            //判斷是否只普通的字符或asc碼(對于中文和表情返回NO)
            BOOL asc = [text canBeConvertedToEncoding:NSASCIIStringEncoding];
            if (asc) {
                s = [text substringWithRange:rg];//因為是ascii碼直接取就可以了不會錯
            }else{
                __block NSInteger idx =0;
                __block NSString  *trimString =@"";//截取出的字串
                //使用字符串遍歷，這個方法能準確知道每個emoji是占一個unicode還是兩個
                [text enumerateSubstringsInRange:NSMakeRange(0, [text length])
                                         options:NSStringEnumerationByComposedCharacterSequences
                                      usingBlock: ^(NSString* substring,NSRange substringRange,NSRange enclosingRange,BOOL* stop) {
                                          if (idx >= rg.length) {
                                              *stop =YES;//取出所需要就break，提高效率
                                              return ;
                                          }
                                          trimString = [trimString stringByAppendingString:substring];
                                          idx++;
                                      }];
                s = trimString;
            }
            //rang是指從當前光標處進行替換處理(注意如果執行此句后面返回的是YES會觸發didchange事件)
            [textView setText:[textView.text stringByReplacingCharactersInRange:range withString:s]];
            //既然是超出部分截取了，哪一定是最大限制了。
            self.lableLimit.text = [NSString stringWithFormat:@"%d/%ld",0,(long)MAX_LIMIT_NUMS];
        }
        return NO;
    }
}

顯示當前可輸入字數/總字數

#pragma mark -顯示當前可輸入字數/總字數
- (void)textViewDidChange:(UITextView *)textView{
    UITextRange *selectedRange = [textView markedTextRange];
    //獲取高亮部分
    UITextPosition *pos = [textView positionFromPosition:selectedRange.start offset:0];
    //如果在變化中是高亮部分在變，就不要計算字符了
    if (selectedRange && pos) {
        return;
    }
    NSString  *nsTextContent = textView.text;
    NSInteger existTextNum = nsTextContent.length;
    if (existTextNum >MAX_LIMIT_NUMS){
        //截取到最大位置的字符(由于超出截部分在should時被處理了所在這里這了提高效率不再判斷)
        NSString *s = [nsTextContent substringToIndex:MAX_LIMIT_NUMS];
        [textView setText:s];
    }
    //不讓顯示負數
    self.lableLimit.text = [NSString stringWithFormat:@"%ld/%d",MAX(0,MAX_LIMIT_NUMS - existTextNum),MAX_LIMIT_NUMS];
}