FileOpenPicker openPicker = new FileOpenPicker();
        openPicker.ViewMode = PickerViewMode.Thumbnail;
        openPicker.SuggestedStartLocation = PickerLocationId.Desktop;
        openPicker.FileTypeFilter.Add(".xml");

        StorageFile file = await openPicker.PickSingleFileAsync();


        if(file!=null)
        {
            var stream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read);

        }
        else
        {
            //
        }