Output Console.WriteLine from WPF Windows Applicat

问题:

Background: I am struggling to add command line and batch processing capabilities to an existing WPF Windows Application. When I detect some options at startup I suppress the window from appearing, do some processing and quit immedietally. Now, because there's no UI I'd like to output some messages to stdout/stderr. Consider following code:

namespace WpfConsoleTest
{
    public partial class App : Application
    {
        protected override void OnStartup(StartupEventArgs e)
        {
            Console.WriteLine("Start");
            System.Threading.Thread.Sleep(1000);
            Console.WriteLine("Stop");
            Shutdown(0);
        }
    }
}

When I run from command line I would expect following output:

Start
Stop

But instead:

C:\test>WpfConsoleTest.exe

C:\test>

You can redirect output, though:

C:\test>WpfConsoleTest.exe > out.txt

C:\test>type out.txt
Start
Stop

Redirecting to CON does not work, unfortunately:

C:\test>WpfConsoleTest.exe > CON

C:\test>

Another problem is that WpfConsoleTest.exe quits immedietaly after start. So:

C:\test>WpfConsoleTest.exe > out.txt & type out.txt

C:\test>

But:

C:\test>WpfConsoleTest.exe > out.txt & ping localhost > nul & type out.txt
Start
Stop

The best solution I was able to come with so far is to use start /B /wait:

C:\test>start /B /wait WpfConsoleTest.exe > out.txt & type out.txt
Start
Stop

This approach is mostly ok - if you wrap it up in a bat you can preserve error code and so on. The one huge downfall is that you get output after application ends, i.e. there's no way you can track progress, you have to wait for whatever is going on to finish.

Therefore, my question is: How to output to parent console from WPF Windows Application? Also, why is so hard to grab stdout/stderr from WPF?

I know that I could change application type to Console Application in project settings, but this has a nasty side effect - console window is visible all the time, even if you simply double click the exe. This solution also won't do, because it create a new console, even if application was run from cmd.

EDIT: to clarify, I want my app to output to the existing console if there is one and not to create a new one if it is missing.

回答1:

After digging up a bit, I found this answer. The code is now:

namespace WpfConsoleTest
{
    public partial class App : Application
    {
        [DllImport("Kernel32.dll")]
        public static extern bool AttachConsole(int processId);

        protected override void OnStartup(StartupEventArgs e)
        {
            AttachConsole(-1);
            Console.WriteLine("Start");
            System.Threading.Thread.Sleep(1000);
            Console.WriteLine("Stop");
            Shutdown(0);
        }
    }
}

Calling the exe directly still has a nasty side effect, connected with the call returning immediately:

C:\test>WpfConsoleTest.exe

C:\test>Start
Stop

^^^^
The cursor will stay here waiting for the user to press enter!

The solution is, once again, to use start:

C:\test>start /wait WpfConsoleTest.exe
Start
Stop

Thanks for input!

回答2:

What I've done in the past is to make it a console application and call P/Invoke to hide the app's associated Console window once I've shown my WPF Window:

//added using statements per comments...
using System.Diagnostics;
using System.Runtime.InteropServices;

    internal sealed class Win32
    {
        [DllImport("user32.dll")]
        static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

        public static void HideConsoleWindow()
        {
            IntPtr hWnd = Process.GetCurrentProcess().MainWindowHandle;

            if (hWnd != IntPtr.Zero)
            {
                ShowWindow(hWnd, 0); // 0 = SW_HIDE
            }
        }
    }

回答3:

A WPF application will not have a console by default, but you can easily create one for it and then write to it just like in a console app. I've used this helper class before:

public class ConsoleHelper
{
    /// <summary>
    /// Allocates a new console for current process.
    /// </summary>
    [DllImport("kernel32.dll")]
    public static extern Boolean AllocConsole();

    /// <summary>
    /// Frees the console.
    /// </summary>
    [DllImport("kernel32.dll")]
    public static extern Boolean FreeConsole();
}

To use this in your example, you should be able to do this:

namespace WpfConsoleTest
{
    public partial class App : Application
    {
        protected override void OnStartup(StartupEventArgs e)
        {
            ConsoleHelper.AllocConsole(); 
            Console.WriteLine("Start");
            System.Threading.Thread.Sleep(1000);
            Console.WriteLine("Stop");
            ConsoleHelper.FreeConsole();
            Shutdown(0);
        }
    }
}

And now, if you run it from the command line, you should see "Start" and "Stop" written to the console.

回答4:

In the project properties, you can change the project type from a Windows application to a Console application, and AFAIK the only difference is that you get a console to use throughout the application's lifetime. I haven't tried it with WPF though.

If you want to open and close a console, you should use Alloc/FreeConsole, but it is usually simpler to change the project type.