iOS UITextView限制输入

举个例子：限制输入字符为200

#pragma mark - TextView Delegate
-(void)textViewDidChange:(UITextView*)textView{
    if ([textView.text length] == 0) {
        [self.placeStrLabel setHidden:NO];
    }else{
        [self.placeStrLabel setHidden:YES];
    }
    [self updateRemainCount];
    if (_textViewBlock) {
        _textViewBlock(textView.text);
    }
    UITextRange *selectedRange = [textView markedTextRange];
    //获取高亮部分
    UITextPosition *pos = [textView positionFromPosition:selectedRange.start offset:0];
    //如果在变化中是高亮部分在变，就不要计算字符了
    if(selectedRange && pos) {return;}
    self.lengthLabel.text = [NSString stringWithFormat:@"%lu/200", (unsigned long)textView.text.length];
    if( (unsigned long)textView.text.length>self.MaxCount) {
        // 对超出的部分进行剪切
        textView.text= [textView.text substringToIndex:self.MaxCount];
        self.lengthLabel.text = @"200/200";
    }
}
- (void)updateRemainCount {
    long count = MAX(0, (int)(0 + self.messageTextView.text.length));
    self.lengthLabel.text = [NSString stringWithFormat:@"%ld/%ld",count,(long)self.MaxCount];
}