问加载大量图像(OutOfMemory异常)。如何直接从硬盘加载图像？

EN

public async void walk(StorageFolder folder)
    {
        IReadOnlyList<StorageFolder> subDirs = null;
        subDirs = await folder.GetFoldersAsync();
        foreach (var subDir in subDirs)
        {
            await SampleDataSource.AddGroupForFolderAsync(subDir.Path);
            walk(subDir);
        }
    }

public static async Task<bool> AddGroupForFolderAsync(string folderPath)
    {
        if (SampleDataSource.GetGroup(folderPath) != null) return false;
        StorageFolder fd = await StorageFolder.GetFolderFromPathAsync(folderPath);
        IReadOnlyList<StorageFile> fList1 = await fd.GetFilesAsync();
        List<StorageFile> fList2 = new List<StorageFile>();
        foreach (var file in fList1)
        {
            string ext = Path.GetExtension(file.Path).ToLower();
            if (ext == ".jpg" || ext == ".png" || ext == ".jpeg") fList2.Add(file);
        }
        if (fList2.Count != 0)
        {
            var folderGroup = new SampleDataGroup(
                uniqueId: folderPath,
                title: fd.Path,
                subtitle: null,
                imagePath: null,
                description: "Description goes here");
            foreach (var i in fList2)
            {
                StorageFile fl = await StorageFile.GetFileFromPathAsync(i.Path);
                IRandomAccessStream Stream = await fl.OpenAsync(FileAccessMode.Read);
                BitmapImage pict = new BitmapImage();
                pict.SetSource(Stream);
                if (pict != null && folderGroup.Image == null)
                {
                    folderGroup.SetImage(pict);
                }
                var dataItem = new SampleDataItem(
                    uniqueId: i.Path,
                    title: i.Path,
                    subtitle: null,
                    imagePath: pict,
                    description: "Decription goes here",
                    content: "Content goes here",
                    @group: folderGroup);
                folderGroup.Items.Add(dataItem);
            }
            AllGroups.Add(folderGroup);
            return true;
        }
        else { return false; }
    }