How to change grid background image in codebehind?

Question

I used:

            StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///d:/Pictures/background1.png"));
            BitmapImage image = new BitmapImage();
            IRandomAccessStream ram = await file.OpenAsync(FileAccessMode.Read);
            await image.SetSourceAsync(ram);

            grid.Background = new ImageBrush() { ImageSource = image };

and:

 ImageBrush brush = new ImageBrush();
          BitmapImage bitmapImage = new BitmapImage(new Uri("ms-appx:/d:/pictures/background2.jpg"));
           brush.ImageSource = bitmapImage;
           
            Grid.Background = brush;
            Source = new BitmapImage(new Uri("ms-appx:/d:/pictures/background2.jpg"));

Both methods do not work. What's wrong?