TextView里限制输入字数的方法

- (void)textViewDidChange:(UITextView *)textView{    NSString *str = [textView textInRange:textView.markedTextRange];    if (![str isEqualToString:@""]) {        return;    }     _labelNumWord.text = [NSString stringWithFormat:@"%ld/500字",textView.text.length>Maxtext_length?Maxtext_length:textView.text.length];    if (textView.text.length > Maxtext_length) {        textView.text = [textView.text substringToIndex:Maxtext_length];//这儿是重点    }}