Change theme before ExportToFile

After some investigation we discovered that we were not able to reproduce this in any of our automation tests, however, we were able to reproduce it in-app by modifying the Export and Screenshot Options example.

Here is our modified code which reproduces the issue:

    private void ExportToPng(object sender, RoutedEventArgs e)
    {
        var saveFileDialog = CreateFileDialog("PNG | *.png");

        if (saveFileDialog.ShowDialog() == true)
        {
            ThemeManager.SetTheme(sciChart, "Oscilloscope");
            sciChart.ExportToFile(saveFileDialog.FileName, ExportType.Png, false);
            ThemeManager.SetTheme(sciChart, "SciChartv4Dark");                   
        }
    }

The above code exports with the default theme (Dark). It does not have time to switch the theme before export. This is most likely due to the Style bindings in our themes which have not evaluated at the point where the ExportToFile call is made.

We discovered as you have, that having this setting:

sciChart.ExportToFile(saveFileDialog.FileName, ExportType.Png, true);

Or this setting

sciChart.ExportToFile(saveFileDialog.FileName, ExportType.Png, false, new Size(sciChart.ActualWidth, sciChart.ActualHeight));

Resolves the issue. This is because the use of Size? parameter or bool useXamlRenderSurface internally forces SciChart to recreate itself in memory (a copy) for rendering off-screen.

We also found that waiting to export like this worked:

    private void ExportToPng(object sender, RoutedEventArgs e)
    {
        var saveFileDialog = CreateFileDialog("PNG | *.png");

        if (saveFileDialog.ShowDialog() == true)
        {
            ThemeManager.SetTheme(sciChart, "BrightSpark");
            sciChart.Dispatcher.BeginInvoke(new Action(() =>
            {
                sciChart.ExportToFile(saveFileDialog.FileName, ExportType.Png, false);
                ThemeManager.SetTheme(sciChart, "SciChartv4Dark");
            }), DispatcherPriority.ApplicationIdle);                                
        }
    }

This forces the application to wait until all Databindings have resolved. You will momentarily see the theme flicker to BrightSpark theme before the export then back to SciChartv4Dark.

In short, I don’t think we can ‘fix’ this internally as forcing databindings to resolve is quite hacky but hopefully one of the above workarounds should suffice!

Best regards,
Andrew