Textfield字符数限制，最后一个字符使用中文拼音无法输入时的问题

1. [self.textField.rac_textSignal subscribeNext:^(NSString * _Nullable x) {
   UITextRange *range = [self.textField markedTextRange];
   //获取高亮部分
   UITextPosition *position = [self.textField positionFromPosition:range.start offset:0];
   if (!position) {
   if (x.length > 50) {
   [###NoticeView showNoticeViewWithString:@"最多输入50个字符"];
   self.textField.text = [x substringToIndex:50];
   }
   }
   }];

2. [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textFieldDidChange:) name:UITextFieldTextDidChangeNotification object:self.textView];
   

• (void)textFieldDidChange:(NSNotification *)notification {
  UITextField *textField = notification.object;
  UITextRange *range = [textField markedTextRange];
  //获取高亮部分
  UITextPosition *position = [textField positionFromPosition:range.start offset:0];
  if (!position) {
  if (textField.text.length > 50) {
  [###NoticeView showNoticeViewWithString:@"最多输入50个字符"];
  textField.text = [textField.text substringToIndex:50];
  }
  }
  }