STTextView可以设置placeHolder和字符个数，达到字符限制不能再输入；另外还添加了字符变化的block回调，方便开发者使用。

#define MAXLENGTH 100STTextView *textView = [[STTextView alloc] initWithFrame:CGRectMake(20, 84, self.view.bounds.size.width - 40, 120)];    textView.placeholder = [NSString stringWithFormat:@"写点什么吧，最多%@个字", @(MAXLENGTH)];    textView.maxLength = MAXLENGTH;    textView.font = [UIFont systemFontOfSize:15];    [textView setTextDidChangeBlock:^(UITextView *textView) {        _countLabel.text = [NSString stringWithFormat:@"还可以写%@个字", @(MAXLENGTH - textView.text.length)];    }];    textView.layer.borderColor = [UIColor lightGrayColor].CGColor;textView.layer.borderWidth = 1.0;textView.layer.opacity = .7;[self.view addSubview:textView];