Question

How to make a splash screen static until the app loads then hide when app is loaded?

This is how it is in wp7 phonegap.

public partial class MainPage : PhoneApplicationPage
{
    private WebBrowserHelper _browserHelper;
    // Constructor
    public MainPage()
    {    
        InitializeComponent();
        this.PGView.Loaded += GapBrowser_Loaded;

        _browserHelper = new WebBrowserHelper(PGView.Browser);
        this.PGView.Browser.ScriptNotify += Browser_ScriptNotify;
    }

    private void GapBrowser_Loaded(object sender, RoutedEventArgs e)
    {
        this.PGView.Loaded -= GapBrowser_Loaded;
        Storyboard _storyBoard = new Storyboard();
        DoubleAnimation animation = new DoubleAnimation()
        {
            From = 0,
            Duration = TimeSpan.FromSeconds(0.6),
            To = 90
        };
        Storyboard.SetTarget(animation, SplashProjector);
        Storyboard.SetTargetProperty(animation, new PropertyPath("RotationY"));
        _storyBoard.Children.Add(animation);
        _storyBoard.Begin();
        _storyBoard.Completed += Splash_Completed;
    }

    void Splash_Completed(object sender, EventArgs e)
    {
        (sender as Storyboard).Completed -= Splash_Completed;
        LayoutRoot.Children.Remove(SplashImage);
    }

    private void Browser_ScriptNotify(object sender, NotifyEventArgs e)
    {
        // if a page notifies that it should not be scrollable, disable
        // scrolling.
        if (e.Value == "noScroll")
        {
            _browserHelper.ScrollDisabled = true;
        }
    }

}

Answer 1

if you only need a simple splash picture, why not change SplashScreenImage.jpg in app ?

i do not very clear why WebBrowserHelper

from your code , i can see you display your picture after mainpage loaded. because you call
_storyBoard.Begin(); in GapBrowser_Loaded event handle