Can't read all files properly from StorageFile in Windows 8 metro application

Question

I'm developing a simple application in Windows 8 metro applications and I m trying to retrieve files from PicturesLibrary, the code I put is the following :

public async void Initialize()
{
    IReadOnlyList<StorageFile> storageFiles = await KnownFolders.PicturesLibrary.GetFilesAsync();              
    foreach (var storageFile in storageFiles)
    {   
        BitmapImage bitmapImage = new BitmapImage();
        FileRandomAccessStream stream = (FileRandomAccessStream)await storageFile.OpenAsync(FileAccessMode.Read);
        bitmapImage.SetSource(stream);
        Image image = new Image();
        image.Source = bitmapImage;
        Images.Add(image);
    }
}

then I show these images using their ImageSource. The problem that I am meeting is that sometimes it shows them all, somethimes one or two , sometimes it deosn't show any image, I don't understand if this is because of the awaitable method GetFileAsync() or other things I may be missing.

Thanks in advance :)

Answer 1

I would guess it's just a timing issue, but doing a breakpoint or trace point in the foreach would tell for sure.

Try changing this to return Task and then await it in the caller of you can

Answer 2

I think your problem will be this line.

FileRandomAccessStream stream = (FileRandomAccessStream)await storageFile.OpenAsync(FileAccessMode.Read);

Awaiting inside a loop is likely going to give you some odd scope issues.
The first thing I would try is switching the first two lines of this loop around.

FileRandomAccessStream stream = (FileRandomAccessStream)await storageFile.OpenAsync(FileAccessMode.Read);
BitmapImage bitmapImage = new BitmapImage();

It could be that the bitmapImage reference is being repointed on you. If this doesn't help though, you might need to look at the .ContinueWith method.

storageFile.OpenAsync(FileAccessMode.Read).ContinueWith(task => {
  FileRandomAccessStream stream = (FileRandomAccessStream)task.Result;
  BitmapImage bitmapImage = new BitmapImage();
  bitmapImage.SetSource(stream);
  Image image = new Image();
  image.Source = bitmapImage;
  Images.Add(image);
});

Answer 3

Ok, I found the solution for this thanks to you guys , I had to rearrange the code little bit,

public async Task Initialize()
        {   
            IReadOnlyList<StorageFile> storageFiles = await KnownFolders.PicturesLibrary.GetFilesAsync();              
            foreach (var storageFile in storageFiles)
            {
                var image = new Image();
                image.Source = await GetBitmapImageAsync(storageFile);
                Images.Add(image);
            }
        }

        public async Task<BitmapImage> GetBitmapImageAsync(StorageFile storageFile)
        {
            BitmapImage bitmapImage = new BitmapImage();
            IAsyncOperation<IRandomAccessStream> operation = storageFile.OpenAsync(FileAccessMode.Read);
            IRandomAccessStream stream = await operation;
            bitmapImage.SetSource(stream);
            return bitmapImage;
        }

then call all that in the OnNavigateTo event since the constructor can't be async

 protected override async void OnNavigatedTo(NavigationEventArgs e)
        {
            _imageList = new ImagesList();
            await _imageList.Initialize();
            foreach (var image in _imageList.Images)
            {
                Image img = new Image() { Source = image.Source };
                img.Width = img.Height = 200;
                img.Margin = new Thickness(20, 0, 20, 0);
                img.ImageFailed += image_ImageFailed;
                img.PointerEntered += img_PointerEntered;
                img.PointerExited += img_PointerExited;
                sp_MainStackPanel.Children.Add(img);
            }
        }

thanks again guys !