Missing images in FlowDocument saved as XPS document

问题

I am having some difficulties getting images contained in a FlowDocument to show when the FlowDocument is saved as an XPS document.

Here is what I do:

1. Create an image using the Image control of WPF. I set the image source bracketed by calls to BeginInit/EndInit.
2. Add the image to the FlowDocument wrapping it in a BlockUIContainer.
3. Save the FlowDocument object to an XPS file using a modified version of this code.

If I then view the saved file in the XPS viewer, the image is not shown. The problem is that the images are not loaded until actually shown on the screen by WPF so they are not saved to the XPS file. Hence, there is a workaround: If I first show the document on screen using the FlowDocumentPageViewer and then save the XPS file afterwards, the image is loaded and shows up in the XPS file. This works even if the FlowDocumentPageViewer is hidden. But that gives me another challenge. Here is what I wish to do (in pseudocode):

void SaveDocument()
{
    AddFlowDocumentToFlowDocumentPageViewer();
    SaveFlowDocumentToXpsFile();
}

This of course does not work since the FlowDocumentPageViewer never gets a chance to show its contents before the document is saved to the XPS file. I tried wrapping SaveFlowDocumentToXpsFile in a call to Dispatcher.BeginInvoke but it did not help.

My questions are:

1. Can I somehow force the images to load before saving the XPS file without actually showing the document on screen? (I tried fiddling with BitmapImage.CreateOptions with no luck).
2. If there is no solution to question #1, is there a way to tell when FlowDocumentPageViewer has finished loading its contents so that I know when it is save to create the XPS file?

回答1:

The eventual solution was the same as you came to, which is to put the document in a viewer and briefly show it on screen. Below is the helper method that I wrote to do this for me.

private static string ForceRenderFlowDocumentXaml = 
@"<Window xmlns=""http://schemas.microsoft.com/netfx/2007/xaml/presentation""
          xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml"">
       <FlowDocumentScrollViewer Name=""viewer""/>
  </Window>";

public static void ForceRenderFlowDocument(FlowDocument document)
{
    using (var reader = new XmlTextReader(new StringReader(ForceRenderFlowDocumentXaml)))
    {
        Window window = XamlReader.Load(reader) as Window;
        FlowDocumentScrollViewer viewer = LogicalTreeHelper.FindLogicalNode(window, "viewer") as FlowDocumentScrollViewer;
        viewer.Document = document;
        // Show the window way off-screen
        window.WindowStartupLocation = WindowStartupLocation.Manual;
        window.Top = Int32.MaxValue;
        window.Left = Int32.MaxValue;
        window.ShowInTaskbar = false;
        window.Show();
        // Ensure that dispatcher has done the layout and render passes
        Dispatcher.CurrentDispatcher.Invoke(DispatcherPriority.Loaded, new Action(() => {}));
        viewer.Document = null;
        window.Close();
    }
}

Edit: I just added window.ShowInTaskbar = false to the method as if you were quick you could see the window appear in the taskbar.

The user will never "see" the window as it is positioned way off-screen at Int32.MaxValue - a trick that was common back in the day with early multimedia authoring (e.g. Macromedia/Adobe Director).

For people searching and finding this question, I can tell you that there is no other way to force the document to render.

HTH,

回答2:

Couple things... You sure the image is sized before its written? Usually you have to call Measure on the control so that it may size itself accordingly (infinity lets the control expand to its Width and Height)

image.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));

Also, sometimes you have to bump the UI thread so that everything gets updated in the control

Dispatcher.Invoke(DispatcherPriority.Render, new Action(() =>{}));

回答3:

You do not have to display the document in order to have images saved into the xps. Are you calling commit on the XpsSerializationManager?

FlowDocument fd = new FlowDocument();

        fd.Blocks.Add(new Paragraph(new Run("This is a test")));

        string image = @"STRING_PATH";

        BitmapImage bi = new BitmapImage();
        bi.BeginInit();
        bi.UriSource = new Uri(image, UriKind.RelativeOrAbsolute);
        bi.CacheOption = BitmapCacheOption.OnLoad;
        bi.EndInit();
        MemoryStream ms = new MemoryStream();
        Package pkg = Package.Open(ms, FileMode.Create, FileAccess.ReadWrite);
        Uri pkgUri = bi.UriSource;

        PackageStore.AddPackage(pkgUri, pkg);


        Image img = new Image();
        img.Source = bi;

        BlockUIContainer blkContainer = new BlockUIContainer(img);

        fd.Blocks.Add(blkContainer);


        DocumentPaginator paginator = ((IDocumentPaginatorSource)fd).DocumentPaginator;

      using (XpsDocument xps = new XpsDocument(@"STRING PATH WHERE TO SAVE FILE", FileAccess.ReadWrite, CompressionOption.Maximum))
        {
            using (XpsSerializationManager serializer = new XpsSerializationManager(new XpsPackagingPolicy(xps), false))
            {
                serializer.SaveAsXaml(paginator);
                serializer.Commit();
            }
        }

来源：https://stackoverflow.com/questions/2425154/missing-images-in-flowdocument-saved-as-xps-document