Question

I have a simple issue, but the solution appears to be tricky. I want to print using the WPF control canvas during a loop; but for each iteration, I want to udpate the canvas control.

If I want to print a canvas control in WPF, I can simply call

PrintDialog dialog = new PrintDialog();
dialog.PrintVisual(this.canvas, "");

And it prints as expected to my default printer. Wonderful.

However, if I want to perform this multiple times in a loop and make an update to the canvas during each iteration, only the final iteration of the loop is printed.

    private void methodName()
    {
        for (int i = 0; i < 2; i++)
        {
            updateTextBox(i.ToString());
            PrintDialog dialog = new PrintDialog();
            dialog.PrintVisual(this.canvas, "");
        }
    }

    private void updateTextBox(string text)
    {
        txtTextBox.Text = text;
    }

Any idea what I need to do to ensure that I get 2 print outs, the first with the txtTextBox.Text value of 0, the second time it has the value of 1?

Answer 1

OK

I solved it.

I removed all the dispatcher object methods so it runs on a single thread.

To update the canvas, I used the canvas.UpdateLayout() method.

I also ensured that the print had finished before updating the next canvas (the next iteration).

private void methodName()
{
    for (int i = 0; i < 2; i++)
    {
        updateTextBox(i.ToString());

        this.canvas.UpdateLayout();

        PrintDialog dialog = new PrintDialog();
        dialog.PrintVisual(this.canvas, "ABC");

        dialog.PrintQueue.Refresh();

        while (dialog.PrintQueue.NumberOfJobs != 0)
        {
            bool isQueued = false;
            foreach (var job in dialog.PrintQueue.GetPrintJobInfoCollection())
            {
                if (job.Name == "ABC")
                    isQueued = true;
            }

            if (!isQueued)
                break;

            Thread.Sleep(500);
            dialog.PrintQueue.Refresh();
        }
    }
}

private void updateTextBox(string text)
{
    txtTextBox.Text = text;
}

I also could have just done thread.sleep(3000) – this worked as it was enough time to ensure the print job had completed, but it was also a little bit ‘hopeful’ and I wanted something more secure.

Thank you to everyone for your suggestions.