Switching between two windows in C++ win32 - c++

Question

i'm building an app in pure c++/win32. it contains two separately used windows. when i switch to 2nd window first time, it shows perfectly. closing it and reverting to first window works fine too, but when i try to switch to 2nd window again, it never shows. i wonder, what am i doing wrong?
#include <windows.h>
#include <windowsx.h>
HWND mainWnd, subWnd;
HINSTANCE hInst;
HWND btnShowSubWindow;
LRESULT CALLBACK MainWndProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam) {
switch(Message) {
case WM_CREATE:{
btnShowSubWindow = CreateWindow("button", "Show 2nd window", WS_CHILD|WS_VISIBLE|BS_PUSHBUTTON,
50,50,150,20,
hwnd,(HMENU)1000, hInst, NULL);
break;
}
case WM_COMMAND:{
switch(LOWORD(wParam)){
case 1000:{
ShowWindow(mainWnd, SW_HIDE);
ShowWindow(subWnd, SW_SHOW);
break;
}
}
break;
}
case WM_CLOSE:{
if (MessageBox(hwnd, "Really quit?", "My application", MB_OKCANCEL) == IDOK)
{
DestroyWindow(hwnd);
}
break;
}
/* Upon destruction, tell the main thread to stop */
case WM_DESTROY: {
PostQuitMessage(0);
break;
}
/* All other messages (a lot of them) are processed using default procedures */
default:
return DefWindowProc(hwnd, Message, wParam, lParam);
}
return 0;
}
LRESULT CALLBACK SubWndProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam) {
switch(Message) {
case WM_CLOSE:{
CloseWindow(hwnd);
ShowWindow(mainWnd, SW_SHOW);
break;
}
/* All other messages (a lot of them) are processed using default procedures */
default:
return DefWindowProc(hwnd, Message, wParam, lParam);
}
return 0;
}
void CreateMainWnd(){
WNDCLASSEX wc; /* A properties struct of our window */
/* zero out the struct and set the stuff we want to modify */
memset(&wc,0,sizeof(wc));
wc.cbSize = sizeof(WNDCLASSEX);
wc.lpfnWndProc = MainWndProc; /* This is where we will send messages to */
wc.hInstance = hInst;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
/* White, COLOR_WINDOW is just a #define for a system color, try Ctrl+Clicking it */
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wc.lpszClassName = "MainWindowClass";
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION); /* Load a standard icon */
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION); /* use the name "A" to use the project icon */
if(!RegisterClassEx(&wc)) {
MessageBox(NULL, "Window Registration Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
return;
}
mainWnd = CreateWindowEx(WS_EX_CLIENTEDGE,wc.lpszClassName,"Main window",WS_VISIBLE|WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, /* x */
CW_USEDEFAULT, /* y */
640, /* width */
480, /* height */
NULL,NULL,hInst,NULL);
if(mainWnd == NULL) {
MessageBox(NULL, "Window Creation Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
return;
}
}
void CreateSubWnd(){
WNDCLASSEX wc; /* A properties struct of our window */
/* zero out the struct and set the stuff we want to modify */
memset(&wc,0,sizeof(wc));
wc.cbSize = sizeof(WNDCLASSEX);
wc.lpfnWndProc = SubWndProc; /* This is where we will send messages to */
wc.hInstance = hInst;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
/* White, COLOR_WINDOW is just a #define for a system color, try Ctrl+Clicking it */
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wc.lpszClassName = "SubWindowClass";
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION); /* Load a standard icon */
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION); /* use the name "A" to use the project icon */
if(!RegisterClassEx(&wc)) {
MessageBox(NULL, "Window Registration Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
return;
}
subWnd = CreateWindowEx(WS_EX_CLIENTEDGE,wc.lpszClassName,"Secondary window",WS_VISIBLE|WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, /* x */
CW_USEDEFAULT, /* y */
640, /* width */
480, /* height */
NULL,NULL,hInst,NULL);
if(subWnd == NULL) {
MessageBox(NULL, "Window Creation Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
return;
}
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
MSG msg; /* A temporary location for all messages */
hInst = hInstance;
CreateMainWnd();
CreateSubWnd();
ShowWindow(mainWnd, nCmdShow);
ShowWindow(subWnd, SW_HIDE);
/*
This is the heart of our program where all input is processed and
sent to WndProc. Note that GetMessage blocks code flow until it receives something, so
this loop will not produce unreasonably high CPU usage
*/
while(GetMessage(&msg, NULL, 0, 0) > 0) { /* If no error is received... */
TranslateMessage(&msg); /* Translate key codes to chars if present */
DispatchMessage(&msg); /* Send it to WndProc */
}
return msg.wParam;
}
i'm using Dev-C++ 5.11.
Addition #1:
i read the answer and i changed MainWndProc's WM_COMMAND handler a bit. now it looks like that:
switch(LOWORD(wParam)){
case 1000:{
ShowWindow(mainWnd, SW_HIDE);
if(subWnd!=NULL)
ShowWindow(subWnd, SW_SHOW);
else
ShowWindow(hwnd, SW_SHOW);
break;
}
i also added a WM_DESTROY handler to SubWndProc:
case WM_DESTROY:{
return 1;
break;
}
if subWnd was destroyed then mainWnd should reappear but it doesn't. i guess that something screws up the contents of subWnd after it hides.

Answer 1

OK, you're calling CloseWindow which minimizes the subwindow. To restore a minimized window, you need to use SW_RESTORE rather than SW_SHOW.

Answer 2

The default action when a user closes a window (by pressing the × in the upper right or through the taskbar) is, that it get's destroyed and it's HWND turns invald. ShowWindow can hide and show existing windows, but it can't resurrect the "dead".
What you can do however is, that you implement a handler for the WM_CLOSE message that hides the window, instead of destroying it. But you must make sure, that once all windows are hidden you actually quit the program, or some other way give the user to interact.
However creating windows is kind of cheap, so the better solution is, to let the windows get destroyed and just to create a new window as replacement.