Windows 8 C＃将ScrollerViewer状态保存在Frame.Navigate

Question

I need to save the position of my ScrollViewer so that when I navigate to a page and hit the back arrow, it will still be at the position it was.

I'm using:

protected override void LoadState(Object navigationParameter, Dictionary<String, Object> pageState)
        {
            base.LoadState(navigationParameter, pageState);
            if (pageState != null && pageState.ContainsKey("ScrollerPosition"))
            {
                mainScrollViewer.ScrollToHorizontalOffset((double) pageState["ScrollerPosition"]);
            }
        }

and

protected override void SaveState(Dictionary<String, Object> pageState)
        {
            base.SaveState(pageState);
            pageState["ScrollerPosition"] = mainScrollViewer.HorizontalOffset;
        }

but it isn't restoring the state it was at. What am I doing wrong? (I'm very new to Windows 8!)

Answer 1

The issue might be that LoadState is called prior to any of your data being loaded. If that is the case, there is no content to scroll so your ScrollToHorizontalOffset call has no effect.

You don't have any detail on how you load your data, so I cannot make a specific recommendation. However, the general solution is to make sure all of your data is loaded prior to your call to set the scroll position.

Answer 2

The place to restore your scroll viewer is in the Loaded event. Add a handler in your constructor:

scrollViewer.Loaded += (sv,event) => ScrollViewerLoaded(sv, event);

(or alternately through the XAML)

Save out the state as you have in SaveState() . Load the value in LoadState() as you have, but instead of using the value immediately cache it until you get to that Loaded event:

void ScrollViewerLoaded(Object sender, RoutedEventArgs event)
{
    mainScrollViewer.ScrollToHorizontalOffset(cachedScrollPosition);
}