为什么子画布上的项目无法使用WPF打印

Question

Trying to construct a page in order to print. I have the following, as an example - based mostly on this http://tech.pro/tutorial/881/printing-in-wpf :

 PrintDialog printDialog = new PrintDialog();
 printDialog.PageRangeSelection = PageRangeSelection.AllPages;
 printDialog.UserPageRangeEnabled = true;
 var doPrint = printDialog.ShowDialog();
 if (doPrint == true)
 {        
            StackPanel myPanel = new StackPanel();
            myPanel.Margin = new Thickness(15);
            Image myImage = new Image();
            myImage.Width = 128;
            myImage.Stretch = Stretch.Uniform;
            myImage.Source = new BitmapImage(new Uri("C:\\Tree.jpg", UriKind.Absolute));
            myPanel.Children.Add(myImage);
            TextBlock myBlock = new TextBlock();
            myBlock.Text = "A Great Image.";
            myBlock.TextAlignment = TextAlignment.Center;
            myPanel.Children.Add(myBlock);

            Canvas canvasL = new Canvas();

            canvasL.Width = 300;
            canvasL.Height = 300;
            canvasL.Background = Brushes.LightSteelBlue;
            myPanel.Children.Add(canvasL);

            Line l = new Line();
            l.X1 = 0;
            l.Y1 = 0;
            l.Y1 = 10000;
            l.Y2 = 10000;

            l.Stroke = Brushes.Black;
            l.StrokeThickness = 5;

            canvasL.Children.Add(l);

            myPanel.Measure(new Size(printDialog.PrintableAreaWidth,
              printDialog.PrintableAreaHeight));
            myPanel.Arrange(new Rect(new Point(0, 0),
              myPanel.DesiredSize));

            printDialog.PrintVisual(myPanel, "A Great Image.");
}

The image shows. The text shows. The canvas shows up as a cobalt-blue square - but the line is nowhere to be seen.

What gives?

Answer 1

You need to set the position of the children on the canvas using attached properties. eg

l.SetValue(Canvas.TopProperty, 10d);
l.SetValue(Canvas.LeftProperty, 10d);
l.SetValue(Canvas.RightProperty, 100d);
l.SetValue(Canvas.BottomProperty, 100d);

Answer 2

Agh. Muppetry.

So the trivial example is bugged as it sets Y1 twice. Fix that and it works.

My more complex case was using ActualWidth which was 0 when being printed (unlike when it was in the main UI), so nothing was being displayed.