How to get the Xamarin.Forms ScrollView control's OnScroll event and get the ContentOffset.Y?

Hello, Every one,

It's my first time to ask question here.

Xamarin.Forms says it abstracted native UI controls from platforms to it's shared controls, but I found lots of properties were not implemented. For example ScrollView control, it has only few properties, I want use the OnScoll event to get the ContentOffset. I think it's a MUST-HAVE property. I can't found what I need in ScrollView control, and how about other controls?

I must ask Xamarin Inc. why. And where's the Xamarin.Forms roadmap?

I just want to build a page looks like the home page of the famous App Tictail. On the home page and some else, when we pull down/up the page, the top image can be zoom in/out, it's very good effect.

With Xcode and Objective-C, it just took me 1 hours to finished the effect.

But using Xamarin.Forms now, I was wondered.

Who can give me an answer?

Sorry for my poor english.

Following is OC code: (Every one here can ask me to get the full project by email: xuebo@live.com)

• (void)addview {
  _W = 1024;
  _H = 1024;

  _w = [[UIScreen mainScreen] bounds].size.width;
  _myimageview.frame = CGRectMake(0, 0, _w, _w * _H / _W);
  _h = _myimageview.frame.size.height;

  UIView *headview = [[UIView alloc]initWithFrame:CGRectMake(0, 0, _w, _h)];
  headview.backgroundColor = [UIColor clearColor];

  UILabel *lab = [[UILabel alloc]initWithFrame:_myimageview.frame];
  lab.text = @不要摸我！;
  lab.font = [UIFont systemFontOfSize:25];
  lab.textColor =[UIColor whiteColor];
  lab.textAlignment = NSTextAlignmentCenter;
  [headview addSubview:lab];
  _mytableview.tableHeaderView = headview;

  _SearchTextField = [[UITextField alloc]initWithFrame:CGRectMake(_w / 7, 50, _w * 5 / 7, 30)];
  _SearchTextField.layer.cornerRadius = 4;
  _SearchTextField.backgroundColor = [UIColor whiteColor];
  _SearchTextField.placeholder = @Search;
  [self.view addSubview:_SearchTextField];
  [self.view bringSubviewToFront:_SearchTextField];

  _field_y = _SearchTextField.center.y;
  }

• (void)scrollViewDidScroll:(UIScrollView *)scrollView {
  CGFloat y = scrollView.contentOffset.y;
  NSLog(@== %f, y);

  if( y<= 0)
  {
  _myimageview.frame=CGRectMake(y * _W / _H / 2, 0, _w - y * _W / _H, _h - y);
  _SearchTextField.alpha = 1;
  }
  else
  {
  _myimageview.frame = CGRectMake(0, -y / 2, _w, _h);
  _SearchTextField.center = CGPointMake(_SearchTextField.center.x, _field_y - y / 4 );
  if (_SearchTextField.center.y >= 20 && _SearchTextField.center.y <= 50)
  {
  _SearchTextField.alpha = (_SearchTextField.center.y - 20) / 30;
  }
  }
  }