Print preview does not render images

Question

I am trying to print a page from my Universal Windows Store app.

I currently have it set up that I get a list of tuples, (contains the data to be put on the printed pages: string and ImageSource), and when the user wants to print, a new PrintPage (custom subclass of Page, styled using XAML) is instantiated, and I set the elements on my PrintPage using this code:

public PrintPage(Tuple<string, ImageSource> tuple) {
    Title.Text = tuple.Item1;
    Image.Source = tuple.Item2;
}

where my XAML is this:

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="*"/>
        <RowDefinition Height="10*"/>
    </Grid.RowDefinitions>
    <TextBlock Name="Title"/>
    <Image Grid.Row="1" Name="Image" Stretch="Uniform"/>
</Grid>

The ImageSource is rendered using the following code (and displayed on a page to have the user choose what to print):

RenderTargetBitmap Bitmap = new RenderTargetBitmap();
await Bitmap.RenderAsync(DrawingArea); // DrawingArea is a `Grid` containing my elements

Now when I print my page, on the preview and on the printed page, I cannot see my image. What am I doing wrong?

just a guess, but don't you need to await RenderAsync? – O.O Sep 10 '15 at 15:56 — O.O, Sep 10 '15 at 15:56
Yes, that is a typo, edited my question – vrwim Sep 10 '15 at 15:59 — vrwim, Sep 10 '15 at 15:59

score 1 · Answer 1 · answered Oct 24 '18 at 08:20

It wont show because it is a RenderTargetBitmap, you need to convert it to a BitmapImage like this:


private async void PrintButton_Click(object sender, RoutedEventArgs e)
        {
            var renderTargetBitmap = new RenderTargetBitmap();
            await renderTargetBitmap.RenderAsync(MyControl);

            var bitmapImage = await ConvertToBitmapImage(renderTargetBitmap);

            var grid = new Grid
            {
                HorizontalAlignment = HorizontalAlignment.Stretch,
                VerticalAlignment = VerticalAlignment.Stretch
            };

            var image = new Image
            {
                Source = bitmapImage,
                Stretch = Windows.UI.Xaml.Media.Stretch.Uniform,
                HorizontalAlignment = HorizontalAlignment.Stretch,
                VerticalAlignment = VerticalAlignment.Stretch
            };
            grid.Children.Add(image);

            _printHelper.AddFrameworkElementToPrint(grid);

            await _printHelper.ShowPrintUIAsync("", new PrintHelperOptions
            {
                Orientation = Windows.Graphics.Printing.PrintOrientation.Landscape
            });
        }

        private async Task<BitmapImage> ConvertToBitmapImage(RenderTargetBitmap renderTargetBitmap)
        {
            var pixels = await renderTargetBitmap.GetPixelsAsync();

            var stream = pixels.AsStream();

            var outStream = new InMemoryRandomAccessStream();

            var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, outStream);

            var displayInformation = DisplayInformation.GetForCurrentView();

            encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Ignore, (uint)renderTargetBitmap.PixelWidth, (uint)renderTargetBitmap.PixelHeight, displayInformation.RawDpiX, displayInformation.RawDpiY, pixels.ToArray());

            await encoder.FlushAsync();
            outStream.Seek(0);

            var bitmap = new BitmapImage();
            await bitmap.SetSourceAsync(outStream);

            return bitmap;
        }

Print preview does not render images

1 Answers1