Question

I am working on a Windows 8 Metro Newsreader-App (with C# and XAML). I show the feed-items on a Grouped Items Page (template). A click forwards the user to a detail-page, which I implemented as a Split Page. Therefore, I have an Image-Gallery where the user can navigate from this DetailPage (and back). This works fine. On the ItemDetailPage I have to assign the Data in the LoadState function. The template offers me the following solution:

protected override void LoadState(Object navigationParameter, Dictionary<String, Object> pageState)
{
    // TODO: Assign a bindable group to this.DefaultViewModel["Group"]
    // TODO: Assign a collection of bindable items to this.DefaultViewModel["Items"]

    if (pageState == null)
    {
        // When this is a new page, select the first item automatically unless logical page
        // navigation is being used (see the logical page navigation #region below.)
        if (!this.UsingLogicalPageNavigation() && this.itemsViewSource.View != null)
        {
            this.itemsViewSource.View.MoveCurrentToFirst();
        }
    }
    else
    {
        // Restore the previously saved state associated with this page
        if (pageState.ContainsKey("SelectedItem") && this.itemsViewSource.View != null)
        {
            // TODO: Invoke this.itemsViewSource.View.MoveCurrentTo() with the selected
            //       item as specified by the value of pageState["SelectedItem"]
        }
    }
}

What I did was the following:

protected override void LoadState(Object navigationParameter, Dictionary<String, Object> pageState)
{
    if (pageState == null)
    {
        // When this is a new page, select the first item automatically unless logical page
        // navigation is being used (see the logical page navigation #region below.)
        if (!this.UsingLogicalPageNavigation() && this.itemsViewSource.View != null)
        {
            this.itemsViewSource.View.MoveCurrentToFirst();
        }
    }
    else
    {
        // Restore the previously saved state associated with this page
        if (pageState.ContainsKey("SelectedItem") && this.itemsViewSource.View != null)
        {
        this.itemsViewSource.View.MoveCurrentTo(pageState["SelectedItem"]);
        }
    }

    var item = ArticleDataSource.GetItem((int)navigationParameter);

    if (item != null)
    {
        this.DefaultViewModel["Group"] = item.Group;
        this.DefaultViewModel["Items"] = item.Group.Items;
        if (this.itemsViewSource.View != null) this.itemsViewSource.View.MoveCurrentTo(item); // remove?

        // Register this page as a share source.
        this.dataTransferManager = DataTransferManager.GetForCurrentView();
        this.dataTransferManager.DataRequested += new TypedEventHandler<DataTransferManager, DataRequestedEventArgs>(this.OnDataRequested);
    }
}

1. If I navigate from the OverviewPage to the DetailsPage the selected item (A) is shown.
2. I select an other item (from the list) and the correct details (B) are shown.
3. If I navigate from the DetailsPage to the GalleryPage the images of the correct item (B) are shown.
4. If I now navigate back (to the DetailsPage) not the last selected item (B) but the item I selected (A) to enter DetailsPage is shown.

I am aware of the fact that I changed the order (proposed by the template) and I added if (this.itemsViewSource.View != null) this.itemsViewSource.View.MoveCurrentTo(item); that I’d probably better remove.

I think that the problem (described in step 4) is, that this.itemsViewSource.View is null and therefore (logically) this.itemsViewSource.View.MoveCurrentTo(pageState["SelectedItem"]) doesn’t get executed. Unfortunately, I was unable to find out why or if this is the bug.

Any help or link to a tutorial (which could solve my problem) are really much appreciated! thanks.

Answer 1

The point is to override the navigationParameter as needed by the previous page state. The item is then loaded and selected. Try using

// Override the navigationParameter if a page state is set:
if (pageState != null && pageState.ContainsKey("SelectedItem"))
{
    navigationParameter = pageState["SelectedItem"];
}

var item = ArticleDataSource.GetItem((int)navigationParameter);

if (item != null)
{
    DefaultViewModel["Group"] = item.Group;
    DefaultViewModel["Items"] = item.Group.Items;

    if (itemsViewSource.View != null)
    {
        itemsViewSource.View.MoveCurrentTo(item);
    }
    else
    {
        // A serious error happened here..
    }
}
else
{
    // Oooops, an item disappeared..
}