How to block console from returning with WPF application attached to console while App is still running

Question

I have the following code in WPF entry point

public partial class App : Application
{
    [DllImport("kernel32.dll")]
    static extern bool AttachConsole(int dwProcessId);
    private const int ATTACH_PARENT_PROCESS = -1;

    protected override void OnStartup(StartupEventArgs e)
    {
        if (e.Args.Length == 0)
        {
            // Launch GUI and pass arguments in case you want to use them.
            base.OnStartup(e);
            new MainWindow().ShowDialog();
        }
        else
        {
            //Do command line stuff
            if (e.Args.Contains("-i"))
            {
                // redirect console output to parent process;
                // must be before any calls to Console.WriteLine()
                AttachConsole(ATTACH_PARENT_PROCESS);
                var stopWatch = new Stopwatch();
                stopWatch.Reset();
                stopWatch.Start();

                for (int i = 0; i < 100; i++)
                {
                    Console.WriteLine(i);
                }
                stopWatch.Stop();
                var ts = stopWatch.Elapsed;
                var elapsedTime = $"{ts.Hours:00}:{ts.Minutes:00}:{ts.Seconds:00}.{ts.Milliseconds / 10:00}";
                Console.WriteLine("RunTime " + elapsedTime);               
            }
            else
            {
                AttachConsole(ATTACH_PARENT_PROCESS);
                Console.WriteLine("Incorrect arguments");
            }
        }

        Shutdown();
    }
}

The prompt returns immediately as though my app runs in the background.

I would expect the app to block the console from being returned until the process is completed.

Answer 1

The AttachConsole re-uses the existing console use AllocConsole() instead. This will block the console unless the parent process is running and will close the console as soon as the program finishes execution.

[DllImport("kernel32.dll")]
static extern bool AllocConsole();