Render image from UserControl that has LiveChart

问题

I kept rendering a black/blank image of a UserControl not shown in window. The UserControl contains LiveChart's CartesianChart and few UIElements. First I borrowed solutions from SO: C# chart to image with LiveCharts and Github: Live-Charts/ChartToImageSample.xaml.cs and apply SaveToPng and EncodeVisual on a simple UIControl generated in runtime (not added or shown in window), which works.

Canvas control = new Canvas() { Width=100, Height=100, Background = new SolidColorBrush(Colors.Pink)};
control.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
control.Arrange(new Rect(0, 0, control.DesiredSize.Width, control.DesiredSize.Height));
control.UpdateLayout();
SaveToPng(control, @"C:\Foo.png");

private void SaveToPng(FrameworkElement visual, string fileName)
{
    PngBitmapEncoder encoder = new PngBitmapEncoder();
    EncodeVisual(visual, fileName, encoder);
}

private static void EncodeVisual(FrameworkElement visual, string fileName, BitmapEncoder encoder)
{
    RenderTargetBitmap bitmap = new RenderTargetBitmap((int)visual.ActualWidth, (int)visual.ActualHeight, 96, 96, PixelFormats.Pbgra32);
    bitmap.Render(visual);
    BitmapFrame frame = BitmapFrame.Create(bitmap);
    encoder.Frames.Add(frame);
    using (FileStream stream = File.Create(fileName)) encoder.Save(stream);
}

But when I applied the same logic to a UserControl

UserControl control = new UserControl(params)
// canvas.Children.Add(control);  <-- if comment out, output blank/black image
control.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
control.Arrange(new Rect(0, 0, control.DesiredSize.Width, control.DesiredSize.Height));
foreach (CartesianChart cc in FindVisualChildren<CartesianChart>(control))
{
    cc.Update(true, true); //force chart redraw
}
control.UpdateLayout();
SaveToPng(control, @"C:\Foo.png");

<!-- UserControl XAML -->
<UserControl>
   <Grid>
      <Border>
         <Grid>
            <Label></Label>
            <Label></Label>
            <Label></Label>
            <CartesianChart DisableAnimations="True"></CartesianChart>
         </Grid>
      </Border>
   </Grid>
</UserControl>

That output a blank/black image. And only when I add UserControl into a UIControl existed and visible on the window/XAML will the UserControl gets rendered properly to an image (e.g. canvas.Children.Add(lc)). I then also tried the solution described in SO: How to render a WPF UserControl to a bitmap without creating a window, but I get the identical result - that is I need to first add this UserControl to a visible UIControl, whether or not I perform UpdateLayout on the UserControl.

Why the first example (Canvas) gets rendered, but not the second example (UserControl)? What are the difference and how can I fix this?

回答1:

For me this works fine for only the chart as well as for the whole user control: (Note: be sure your usercontrol has a visible background color, if the background is transparent it will be rendered transparent which most image viewer show as black)

EDIT: ok, I guess my solution won't work if the chart isn't visible. But if you can't get it to work otherwise, why not show the usercontrol in a new window, save it and close that window again?

    public static BitmapSource RenderChartAsImage(FrameworkElement chart)
    {
        RenderTargetBitmap image = new RenderTargetBitmap((int)chart.ActualWidth, (int)chart.ActualHeight,
                                                            96, 96, PixelFormats.Pbgra32);
        image.Render(chart);
        return image;
    }

    public static void SaveChartImage(FrameworkElement chart)
    {
        System.Windows.Media.Imaging.BitmapSource bitmap = RenderChartAsImage(chart);

        Microsoft.Win32.SaveFileDialog saveDialog = new Microsoft.Win32.SaveFileDialog();
        saveDialog.FileName += "mychart";
        saveDialog.DefaultExt = ".png";
        saveDialog.Filter = "Image (*.png)|*.png";

        if (saveDialog.ShowDialog() == true)
        {
            using (FileStream stream = File.Create(saveDialog.FileName))
            {
                System.Windows.Media.Imaging.PngBitmapEncoder encoder = new System.Windows.Media.Imaging.PngBitmapEncoder();
                encoder.Frames.Add(System.Windows.Media.Imaging.BitmapFrame.Create(bitmap));
                encoder.Save(stream);
            }
        }
    }

来源：https://stackoverflow.com/questions/51823020/render-image-from-usercontrol-that-has-livechart

标签

wpf

livecharts