Calling AllocConsole & FreeConsole multiple times and keep In- & Output functionality of Console object in C# .NET

Question

OS: Windows 10 Enterprise 1703 64-bit

I cannot allocate and free a console more than once without loosing the Console.ReadKey() functionality in a windows form application. This question is similiar to Exception when using console window in a form application but the answer is missing out on the Console.ReadKey() function.

The following code works for the first execution only. One receives a new console window and the user has to press any key. On the second execution the text is displayed as well but Console.ReadKey() throws a System.InvalidOperationException.

System.InvalidOperationException: 'Cannot read keys when either application does not have a console or when console input has been redirected from a file. Try Console.Read.'

Left out the DllImport declarations within the static Win32Wrapper class for brevity.

Win32Wrapper.AllocConsole();

// set standard out handle to console window
var ConOut = Win32Wrapper.CreateFile(
    "CONOUT$",
    GenericAccessRight.GENERIC_READ | GenericAccessRight.GENERIC_WRITE,
    ShareMode.FILE_SHARE_WRITE,
    IntPtr.Zero,
    CreationDisposition.OPEN_EXISTING,
    0,
    IntPtr.Zero
);
Win32Wrapper.SetStdHandle(Win32Wrapper.STD_OUTPUT_HANDLE, ConOut);

// set stadard in handle to console window
var ConIn = Win32Wrapper.CreateFile(
    "CONIN$",
    GenericAccessRight.GENERIC_READ | GenericAccessRight.GENERIC_WRITE,
    ShareMode.FILE_SHARE_READ,
    IntPtr.Zero,
    CreationDisposition.OPEN_EXISTING,
    0,
    IntPtr.Zero
);
Win32Wrapper.SetStdHandle(Win32Wrapper.STD_INPUT_HANDLE, ConIn);

Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = true });
Console.SetIn(new StreamReader(Console.OpenStandardInput()));

Console.WriteLine("Hello World!"); // works every time
Console.Read();                    // works every time
Console.ReadKey(true);             // second call: InvalidOperationException

Win32Wrapper.CloseHandle(ConIn)
Win32Wrapper.CloseHandle(ConOut)

return Win32Wrapper.FreeConsole();

This isn't going to work out. Convert your program to be a console app. — David Heffernan
– David Heffernan, Commented Oct 18, 2019 at 13:08
So you'll likely need two distinct executables and some IPC. — David Heffernan
– David Heffernan, Commented Oct 18, 2019 at 13:50

urbanSoft · Accepted Answer · 2019-10-18 13:58:14Z

1

I found a way to simulate the above behaviour by not destroying the console I created before but instead simply hiding and displaying it again.

if (FirstTime)
{
  FirstTime = false;
  Win32Wrapper.SetStdHandle(Win32Wrapper.STD_OUTPUT_HANDLE, HWND.Zero);
  Win32Wrapper.SetStdHandle(Win32Wrapper.STD_INPUT_HANDLE, HWND.Zero);
  Win32Wrapper.AllocConsole(); // show implicitly
}
else
{
  Console.Clear(); // clear => simulate new console
  Win32Wrapper.ShowWindow(Win32Wrapper.GetConsoleWindow(), 5); // show (again)
}

Console.WriteLine("Hello World!");
Console.Read();
Console.ReadKey(true);

Win32Wrapper.ShowWindow(Win32Wrapper.GetConsoleWindow(), 0); // hide

Only the first function call allocates a new console further calls only show the already existing console again. All I need is a static variable to take track of it.

answered Oct 18, 2019 at 13:58

urbanSoft

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Drake Wu Over a year ago

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