保存文件属性导致值不属于范围异常

Question

我有以下代码应该检索画布，保存图像，然后将文件属性写入其中。可悲的是，它在尝试保存属性时崩溃了。它们是字符串形式，属性也需要一个字符串，所以我看不出可能出错的地方：

try
{
    using (Windows.Storage.Streams.IRandomAccessStream stream =
            await file.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite))
    {
        stream.Size = 0;
        await MyInkCanvas.InkPresenter.StrokeContainer.SaveAsync(stream);
    }

    ImageProperties imageProperties = await file.Properties.GetImagePropertiesAsync();
    string title = CanvasGrid.Width + " x " + CanvasGrid.Height;
    imageProperties.Title = title;
    await imageProperties.SavePropertiesAsync();

    //MainPage.NotifyUser("File has been saved!", NotifyType.StatusMessage);
}
catch (Exception ex)
{
    //MainPage.NotifyUser(ex.Message, NotifyType.ErrorMessage);
}

  

价值不在预期范围内。