How to hide / unhide a process in C#?

Question

I am attempting to start an external process in a Visual C# 2010 - Windows Forms application. The goal is to start the process as a hidden window, and unhide the window at a later time.

I've updated my progress:

//Initialization
[DllImport("user32.dll")]
private static extern bool ShowWindow(IntPtr hwnd, int nCmdShow);
[DllImport("user32.dll")]
private static extern bool EnableWindow(IntPtr hwnd, bool enable);
[DllImport("user32.dll")]
private static extern bool MoveWindow(IntPtr handle, int x, int y, int width, 
int height, bool redraw);

SW_SHOW = 5;

The following was placed in my main function:

ProcessStartInfo info = new ProcessStartInfo("process.exe");
info.WindowStyle = ProcessWindowStyle.Hidden;
Process p = Process.Start(info);

p.WaitForInputIdle();
IntPtr HWND = p.MainWindowHandle;

System.Threading.Thread.Sleep(1000);    

ShowWindow(HWND, SW_SHOW);
EnableWindow(HWND, true);
MoveWindow(HWND, 0, 0, 640, 480, true);

However, because the window was started as "hidden," p.MainWindowHandle = 0. I am not able to successfully show the window. I have also tried HWND = p.Handle with no success.

Is there a way to provide a new handle to my window? This could potentially fix my problem.

References:

MSDN ShowWindow

MSDN Forums

How to Import .dll

Answer 1

Finally, the process is operating properly. Thanks to all of your help, I came up with this fix.

The p.MainWindowHandle was 0, so I had to use the user32 FindWindow() function to get the window handle.

//Initialization
int SW_SHOW = 5;

[DllImport("user32.dll",SetLastError=true)]
private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

[DllImport("user32.dll")]
private static extern bool ShowWindow(IntPtr hwnd, int nCmdShow);

[DllImport("user32.dll")]
private static extern bool EnableWindow(IntPtr hwnd, bool enabled);

And in my main function:

ProcessStartInfo info = new ProcessStartInfo();
info.FileName = "notepad";
info.UseShellExecute = true;
info.WindowStyle = ProcessWindowStyle.Hidden;

Process p = Process.Start(info);
p.WaitForInputIdle();
IntPtr HWND = FindWindow(null, "Untitled - Notepad");

System.Threading.Thread.Sleep(1000);

ShowWindow(HWND, SW_SHOW);
EnableWindow(HWND, true);

References:

pinvoke.net: FindWindow()

Edit: Removed WindowShowStyle from the dllImport declaration: you can define this as an int instead. I defined an enum called WindowShowStyle to define the constants outlined in this article. It just better fits my coding patterns to have enums defined instead of using constant or hard-coded values.