saving state between pages when creating a windows 8 app

c#, windows-store-apps

Solution

I did this tutorial too and I found one solution to save the state across pages navigation.

First, override the OnNavigatedFrom in order to save the file token into State Frame:

protected override void OnNavigatedFrom(NavigationEventArgs e)
{
    base.OnNavigatedFrom(e);

    var state = SuspensionManager.SessionStateForFrame(this.Frame);
    state["mruToken"] = mruToken;
}

Override the OnNavigatedTo in order to load the token from the state:

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    base.OnNavigatedTo(e);

    var state = SuspensionManager.SessionStateForFrame(this.Frame);
    if (state != null && state.ContainsKey("mruToken"))
    {
        object value = null;

        if (state.TryGetValue("mruToken", out value))
        {
           // the same code as LoadState to retrieve the image  
        }
    }
}

In fact, I wrote another function to retrieve the image so it can be used in both LoadState and OnNavigatedTo methods.

private async void restoreImage(object value)
{
    if (value != null)
    {
        mruToken = value.ToString();

        // Open the file via the token that you stored when adding this file into the MRU list.
        Windows.Storage.StorageFile file =
            await Windows.Storage.AccessCache.StorageApplicationPermissions.MostRecentlyUsedList.GetFileAsync(mruToken);

        if (file != null)
        {
            // Open a stream for the selected file.
            Windows.Storage.Streams.IRandomAccessStream fileStream =
                await file.OpenAsync(Windows.Storage.FileAccessMode.Read);

            // Set the image source to a bitmap.
            Windows.UI.Xaml.Media.Imaging.BitmapImage bitmapImage =
                new Windows.UI.Xaml.Media.Imaging.BitmapImage();

            bitmapImage.SetSource(fileStream);
            displayImage.Source = bitmapImage;

            // Set the data context for the page.
            this.DataContext = file;
        }
    }
}

Problem

I've been following the Create your first Windows Store app using C# or Visual Basic tutorials provided by Microsoft but am having some problems saving state when navigating between pages. Create your first Windows Store app using C# or Visual Basic Part 3: Navigation, layout, and views Basically I've noticed that if I navigate from the main page to the photo page select a photo, navigate back to the main page and then go to the photo page again it doesn't remember the photo that was selected. I'm using the following code to navigate to the photo page from the main page. ``` private void photoPageButton_Click(object sender, RoutedEventArgs e) { this.Frame.Navigate(typeof(PhotoPage)); } ``` In the photo page the loadstate method is ``` protected async override void LoadState(Object navigationParameter, Dictionary<String, Object> pageState) { if (pageState != null && pageState.ContainsKey("mruToken")) { object value = null; if (pageState.TryGetValue("mruToken", out value)) { if (value != null) { mruToken = value.ToString(); // Open the file via the token that you stored when adding this file into the MRU list. Windows.Storage.StorageFile file = await Windows.Storage.AccessCache.StorageApplicationPermissions.MostRecentlyUsedList.GetFileAsync(mruToken); if (file != null) { // Open a stream for the selected file. Windows.Storage.Streams.IRandomAccessStream fileStream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read); // Set the image source to a bitmap. Windows.UI.Xaml.Media.Imaging.BitmapImage bitmapImage = new Windows.UI.Xaml.Media.Imaging.BitmapImage(); bitmapImage.SetSource(fileStream); displayImage.Source = bitmapImage; // Set the data context for the page. this.DataContext = file; } } } } } ``` The photo page save state is ``` protected override void SaveState(Dictionary<String, Object> pageState) { if (!String.IsNullOrEmpty(mruToken)) { pageState["mruToken"] = mruToken; } } ``` I've noticed that the pagestate is always null when navigated to. Any ideas?

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