win8 metro读取图片

　　　　　　　　　FileOpenPicker openPicker = new FileOpenPicker();
                openPicker.ViewMode = PickerViewMode.Thumbnail;
                openPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
                openPicker.FileTypeFilter.Add(".jpg");
                openPicker.FileTypeFilter.Add(".jpeg");
                openPicker.FileTypeFilter.Add(".png");
                ImageUploadButon.IsEnabled = false;
                SelectedProgressRing.IsActive = true;
                StorageFile file = await openPicker.PickSingleFileAsync();
                
                if (null != file)
                {
                    userTxt.Text = file.Name;

                    using (Stream stream = await file.OpenStreamForReadAsync())
                    {