C ++ MessageBox（Windows.h）-它做什么，如何使其不可见（或等效）？

Question

When I have:

MessageBox(NULL, NULL , "MessageBox", NULL);

A message box comes up and my program works as I desire it to until the user clicks okay on the message box and then the program ends. I tried to put an infinite loop in to have the same effect, but this doesn't work in the same way as the message box does. The reason I don't want the message box is the fact that it obstructs the user's view of the program and if they try to close it then the program stops. So I basically just want to have an invisible message box or something with the same effect.

EDIT: To clarify, the program is a prototype for a game. I am using hooks to find what keys the user is pressing. Here is a simplified version of the program:

#define WM_KEYDOWN                      0x0100
#define _WIN32_WINNT 0x0500

#include <iostream>
#include <windows.h>
#include <winuser.h>

using namespace std;

LRESULT CALLBACK HookProc(int nCode, WPARAM wParam, LPARAM lParam){


PKBDLLHOOKSTRUCT keypointer = (PKBDLLHOOKSTRUCT)(lParam);
if (wParam==WM_KEYDOWN){

    switch(keypointer->vkCode){


        case VK_RIGHT:
            cout << "**RIGHT**";
            goto skip;
        case VK_LEFT:
            cout << "**LEFT**";
            goto skip;
        case VK_DOWN:
            cout << "**DOWN**";
            goto skip;
        case VK_UP: 
            cout << "**UP**";
        skip:
        default:
            cout << "";
    }
}
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd) {


SetWindowsHookEx(WH_KEYBOARD_LL, HookProc, hInstance, 0);

MessageBox(NULL, NULL , "KLMBOX", NULL);

return 0;

}

I just want the program to have the same functionality, but without displaying a message box! I'm not an expert I was just messing around with: http://msdn.microsoft.com/en-us/library/windows/desktop/ms632589(v=vs.85).aspx

Answer 1

Sounds like what you are looking for is a message loop . MessageBox() is doing is two things here: it displays the dialog, but it's also supplying its own message loop internally to process input for the dialog. Low-level hooks require a message loop to function correctly, and your code works with MessageBox just because the message loop that it is supplying is doing the necessary message processing for you. And that's why a plain infinite loop doesn't work as a substitute - it's not processing the messages appropriately.

Here's a simple one you can cut-and-paste:

MSG msg;
while(GetMessage(&msg, NULL, 0, 0))
{
    TranslateMessage(&msg);
    DispatchMessage(&msg);
}

When you decide elsewhere in your code (but still on the same thread) that you want to exit - perhaps when you detect some key combination in the hook - use PostQuitMessage() ; this will post a WM_QUIT message to the thread's queue, and when GetMessage retrieves that, it will return 0 and the loop will exit.

---

Having said all of that, this isn't a good way to write a game in the first place; low-level keyboard hooks are overkill and not really appropriate here. If you want to get keyboard input in a windows app, the simplest thing to do is create your own window, and it will receive WM_KEYDOWN/UP messages as keys are pressed/released.

Answer 2

With your code sample, it looks like you're trying to make a game but structuring it all wrong. A game normally has a main loop in where each iteration you check the input, update the game state and then render. If it's this you want, I would suggest that you look into one of the many open game engines that are out there and try some of the input tutorials. OGRE 3d might be a good place to start, good community and good tutorials.

However, if that is not what you want and you indeed want to play around with hooks, you will need to create a different thread. If you create an infinite loop the system will never get around to handling the hooks.

Probably the easiest way to do what you want to do is to open a window and make it invisible. Creating a window using the raw win32 API that you're using right now is involved and takes quite a bit of code to do. Here is one tutorial that explains the steps involved.

But again, if you are looking to make a simple game, I suggest leveraging an existing engine. You'll make way faster progress that way. Good luck!

Answer 3

I don't understand... do you want a message box or not? If not, why are you calling MessageBox()? I believe the message box is modal, meaning that the user MUST acknowledge it in some way (clicking okay/cancel) before they can return to the parent interface. I believe it is also blocking, meaning that it does not run on a separate thread and will block execution of the thread it was called on until the user closes it.

Your application should not be shutting down just because the user closes the message box unless that is how you have specifically written it. I would need more information and possibly code samples to tell you why that is happening if it is unintended.