一、实现的逻辑很简单且代码量不多，直接贴出源码供方便快速使用。

<UITextViewDelegate>
@property (nonatomic, strong) UITextView *textView;
@property (nonatomic, strong) UILabel *limitLabel;

    _textView = [[UITextView alloc] initWithFrame:CGRectMake(5, 5, MAIN_WIDTH-10, 130.3)];
    _textView.placeHolder = @"请描述您的问题...";
    _textView.returnKeyType = UIReturnKeyDone;
    _textView.delegate = self;
    _textView.textColor = UIColorFromRGB(0xBEBDBD);
    _textView.font = [UIFont systemFontOfSize:15];
    [self addSubview:_textView];
    
    _limitLabel = [[UILabel alloc] initWithFrame:CGRectMake(MAIN_WIDTH/4*3, 130.3, MAIN_WIDTH/4-10, 20)];
    _limitLabel.text = @"0/500";
    _limitLabel.font = [UIFont systemFontOfSize:12];
    _limitLabel.textAlignment = NSTextAlignmentRight;
    _limitLabel.textColor = UIColorFromRGB(0x999999);
    _limitLabel.backgroundColor = [UIColor clearColor];

二、实现TextView代理方法

实时监听TextView输入框的return键，当点击return键时结束编辑的实现思路：判断输入的字是否为\n回车，即按下return键

- (void)textViewDidChange:(UITextView *)textView {
    _limitLabel.text = [NSString stringWithFormat:@"%ld/500",textView.text.length ];
}

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
    NSLog(@"textLength == %ld",textView.text.length);
    if ([text isEqualToString:@"\n"]){ //判断输入的字是否是回车，即按下return
        [self.textView resignFirstResponder];
        return NO;
    }
    if ([self stringContainsEmoji:text] == YES) {
        [PubllicMaskViewHelper showTipViewWith:@"不支持输入Emoji表情符号" inSuperView:self withDuration:1];
        return NO;
    }
    if (textView.text.length + text.length > 500) {
        NSString *allText = [NSString stringWithFormat:@"%@%@",textView.text,text];
        textView.text = [allText substringToIndex:500];
        [PubllicMaskViewHelper showTipViewWith:@"输入不能超过500个字" inSuperView:self withDuration:1];
        return NO;
    }
    return YES;
}

三、过滤所有Emoji表情符号

// 过滤所有表情
- (BOOL)stringContainsEmoji:(NSString *)string {
    __block BOOL returnValue = NO;
    [string enumerateSubstringsInRange:NSMakeRange(0, [string length]) options:NSStringEnumerationByComposedCharacterSequences usingBlock:
     ^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
         
         const unichar hs = [substring characterAtIndex:0];
         // surrogate pair
         if (0xd800 <= hs && hs <= 0xdbff) {
             if (substring.length > 1) {
                 const unichar ls = [substring characterAtIndex:1];
                 const int uc = ((hs - 0xd800) * 0x400) + (ls - 0xdc00) + 0x10000;
                 if (0x1d000 <= uc && uc <= 0x1f77f) {
                     returnValue = YES;
                 }
             }
         } else if (substring.length > 1) {
             const unichar ls = [substring characterAtIndex:1];
             if (ls == 0x20e3) {
                 returnValue = YES;
             }
             
         } else {
             // non surrogate
             if (0x2100 <= hs && hs <= 0x27ff) {
                 returnValue = YES;
             } else if (0x2B05 <= hs && hs <= 0x2b07) {
                 returnValue = YES;
             } else if (0x2934 <= hs && hs <= 0x2935) {
                 returnValue = YES;
             } else if (0x3297 <= hs && hs <= 0x3299) {
                 returnValue = YES;
             } else if (hs == 0xa9 || hs == 0xae || hs == 0x303d || hs == 0x3030 || hs == 0x2b55 || hs == 0x2b1c || hs == 0x2b1b || hs == 0x2b50) {
                 returnValue = YES;
             }
         }
     }];
    
    return returnValue;
}