Problems using the ScrollToAsync() method from ScrollView in the OnAppearing() of a Content Page

Issue

I have in my code behind file made an override to the OnAppearing() method, to do some automatic scrolling to a specific element which is a child inside my ScrollView element in my XAML file. I use the method ScrollToAsync() from the ScrollView element, to Scroll to the element MyBox, which is a BoxView element.

protected override async void OnAppearing()
{
    await HorizontalScrollView.ScrollToAsync(MyBox, ScrollToPosition.Center, false);
    base.OnAppearing();
}

My Problem is here that when the page appear it doesnt scroll to the MyBox element automatically. However I got it to work if I inserted a Task.Delay().

protected override async void OnAppearing()
{
    await System.Threading.Tasks.Task.Delay(1);
    await HorizontalScrollView.ScrollToAsync(MyBox, ScrollToPosition.Center, false);
    base.OnAppearing();
}

My question is why it works, when I insert the delay, and is there any way I can get rid of using the Task.Delay() statement?

Solution

You need to invoke the line in UIThread (Main Thread) like following

protected override async void OnAppearing()
{
    base.OnAppearing();

    Device.BeginInvokeOnMainThread(async ()=> {
        await HorizontalScrollView.ScrollToAsync(MyBox, ScrollToPosition.Center, false);
    });
}

Answered By - Lucas Zhang - MSFT