I am creating an MDI Child Window after selecting "File -> Open" Menu. In the "Open" switch statement I have the window creation function
HWND hwndChild = CreateWindowEx(WS_EX_MDICHILD, childClass, "MDI child", WS_CLIPCHILDREN, 0, 0, 400, 300, hWndClient, MAKEINTRESOURCE(IDM_FIRSTCHILD), GetModuleHandle(NULL), 0);
After that declaration I expected the child MDI window to show but nothing happens. The window handle hwndChild is also different from NULL and the error MessageBox doesn't show.
It seems that the error is in handling the WM_SIZE message inside the WndProc window function.
One solution is to put
return DefFrameProc(hwnd, hWndClient, msg, wParam, lParam);
instead of
return 0;
at the end of WndProc. But this solution is not compatible with the status bar, as it then disappears.
Here is the complete code:
#include <windows.h>
#include <commctrl.h> //per SBARS_SIZEGRIP e STATUSCLASSNAME
#define IDM_OPEN 100
#define IDM_EXIT 101
#define IDM_ABOUT 102
#define IDC_STATUSBAR 103
#define IDM_ARRANGE 104
#define IDM_CASCADE 105
#define IDM_TILE 106
#define IDM_CLOSEALL 107
#define IDM_CLOSE 108
#define ID_CLIENTWND 109
#define IDM_FIRSTCHILD 5000
const char frameClass[] = "myFrameClass";
const char clientClass[] = "mdiclient"; //funziona solo con "mdiclient"
const char childClass[] = "myChildClass";
HWND hWndStatusBar;
HWND hWndClient;
//STEP 5 Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam){
switch (msg){
case WM_CREATE:
//STEP 6: Create Status Bar
hWndStatusBar = CreateWindowEx(0,STATUSCLASSNAME,NULL,
WS_CHILD | WS_VISIBLE | SBARS_SIZEGRIP,
0, 0, 0, 0,
hwnd,
(HMENU)IDC_STATUSBAR,
(HINSTANCE)GetWindowLong(hwnd, GWL_HINSTANCE), NULL);
if(!hWndStatusBar){
MessageBox(NULL, "Failed To Create The Status Bar", "Error", MB_OK | MB_ICONERROR);
return 0;
}
// Establish the number of partitions or 'parts' the status bar will
// have, their actual dimensions will be set in the parent window's
// WM_SIZE handler.
RECT rc;
GetClientRect(hwnd, &rc);
int nHalf = rc.right / 2;
int nParts[4] = { nHalf, nHalf + nHalf / 3, nHalf + nHalf * 2 / 3, -1 };
SendMessage(hWndStatusBar, SB_SETPARTS, 4, (LPARAM)&nParts);
//crea la finestra CLIENT
CLIENTCREATESTRUCT ccs;
// Assign the 'Window' menu.
ccs.hWindowMenu = GetSubMenu(GetMenu(hwnd), 1); // uno perchè così la finestra appare nel secondo menu (partendo da zero) ovvero nel menu 'Windows'
ccs.idFirstChild = IDM_FIRSTCHILD;
// Create the client window. (quella che contiene i child!!)
hWndClient = CreateWindowEx(WS_EX_CLIENTEDGE, clientClass,//FUNZIONA SOLO CON "mdiclient"
NULL,
WS_CHILD | WS_CLIPCHILDREN | WS_VISIBLE,
0, 0, 0, 0,
hwnd,(HMENU)ID_CLIENTWND/*GetMenu(hwnd)*/,GetModuleHandle(NULL),&ccs);
if(hWndClient == NULL) {
MessageBox(NULL, "Client Window Creation Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
return 0;
}
break;
case WM_SIZE:
//resize the parts
GetClientRect(hwnd, &rc);
nHalf = rc.right / 2;
nParts[0] = nHalf; nParts[1] = nHalf + nHalf / 3; nParts[2] = nHalf + nHalf * 2 / 3; nParts[3] = -1;
SendMessage(hWndStatusBar, SB_SETPARTS, 4, (LPARAM)&nParts);
//resize the statusbar
SendMessage(GetDlgItem(hwnd, IDC_STATUSBAR), WM_SIZE,0,0);
break;
case WM_CLOSE:
DestroyWindow(hwnd);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
case WM_COMMAND:
if(LOWORD(wParam) == IDM_EXIT) DestroyWindow(hwnd);
if(LOWORD(wParam) == IDM_ABOUT) MessageBox(hwnd,"ABOUT premuto","ciao",MB_OK);
if(LOWORD(wParam) == IDM_OPEN){
//apre il file...
//TODO
//crea la finestra CHILD
HWND hwndChild = CreateWindowEx(WS_EX_MDICHILD, //extended styles
childClass, //control 'class' name
"MDI child", //control caption
WS_CLIPCHILDREN, //control style
0, //position: left
0, //position: top
400, //width
300, //height
hWndClient, //parent window handle
//control's ID
MAKEINTRESOURCE(IDM_FIRSTCHILD),
GetModuleHandle(NULL), //application instance
0); //user defined info
if(hwndChild == NULL){
MessageBox(hwnd,"Impossibile creare la finestra Child","Errore",MB_ICONERROR);
}
}
break;
default:
//return DefWindowProc(hwnd,msg,wParam,lParam);
return DefFrameProc(hwnd, hWndClient, msg, wParam, lParam); //per tenere conto delle finestre figlie
}
return 0;
}
LRESULT CALLBACK ChildWndProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam)
{
switch(msg) {
case WM_CREATE :
// LPCREATESTRUCT lpCreateStruct = (LPCREATESTRUCT)lParam;
// LPMDICREATESTRUCT lpMDICreateStruct = (LPMDICREATESTRUCT)lpCreateStruct->lpCreateParams;
// FrameParam = lpMDICreateStruct->lParam;
break;
case WM_COMMAND:
break;
/* All other messages (a lot of them) are processed using default procedures */
default:
return DefMDIChildProc(hwnd, msg, wParam, lParam);
}
return 0;
}
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nCmdShow)
{
WNDCLASSEX wc;
HWND hwnd;
MSG msg;
//STEP 1: Registering Frame Class Window
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = CS_HREDRAW | CS_VREDRAW;;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(NULL,IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL,IDC_ARROW);
wc.hbrBackground = (HBRUSH)(COLOR_APPWORKSPACE+1);//(COLOR_WINDOW);
wc.hIconSm = LoadIcon(NULL,IDI_APPLICATION);
wc.lpszMenuName = NULL;
wc.lpszClassName = frameClass;
if(!RegisterClassEx(&wc)){
MessageBox(NULL,"Frame Window Registration Failed!","Error!",MB_ICONEXCLAMATION);
return 0;
}
//la classe CLIENT non la devo registrare?
//STEP 1.2: Registering Child Class Window
wc.lpfnWndProc = (WNDPROC)ChildWndProc;
wc.hIcon = (HICON)LoadImage(0,IDI_APPLICATION,IMAGE_ICON,0,0,LR_SHARED);
wc.hIconSm = LoadImage(hInstance,childClass,IMAGE_ICON,16,16,LR_DEFAULTCOLOR);
wc.hCursor = (HCURSOR)LoadImage(0,IDC_ARROW,IMAGE_CURSOR,0,0,LR_SHARED);
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);//(COLOR_WINDOW);
wc.lpszMenuName = NULL;
wc.lpszClassName = childClass;
if(!RegisterClassEx(&wc)){
MessageBox(NULL,"Child Window Registration Failed!","Error!",MB_ICONEXCLAMATION);
return 0;
}
//STEP 2: Creating the Window
hwnd = CreateWindowEx(WS_EX_CLIENTEDGE,
frameClass,
"046 - Visualizer",
WS_VISIBLE|WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT,CW_USEDEFAULT,600,400,
NULL,NULL,hInstance,NULL);
if(hwnd == NULL){
MessageBox(NULL,"Frame Window Creation Failed!","Error!",MB_ICONEXCLAMATION);
return 0;
}
ShowWindow(hwnd,nCmdShow);
UpdateWindow(hwnd);
//STEP 3: Create Menu
HMENU hMenu = CreateMenu(); //crea un menu vuoto
HMENU hSubMenu; //variabile usata per aggiungere sottomenu ti tipo POPUP
hSubMenu = CreatePopupMenu();
AppendMenu(hSubMenu,MF_STRING,IDM_OPEN,"&Open");
AppendMenu(hSubMenu,MF_STRING,IDM_CLOSE,"&Close");
AppendMenu(hSubMenu, MF_SEPARATOR, 0, NULL);
AppendMenu(hSubMenu,MF_STRING,IDM_EXIT,"&Exit");
AppendMenu(hMenu,MF_STRING|MF_POPUP,(UINT)hSubMenu,"&File"); //aggiunge il sottomenu al menu
hSubMenu = CreatePopupMenu();
AppendMenu(hSubMenu,MF_STRING,IDM_ARRANGE,"Arrange");
AppendMenu(hSubMenu,MF_STRING,IDM_CASCADE,"Cascade");
AppendMenu(hSubMenu,MF_STRING,IDM_TILE,"Tile");
AppendMenu(hSubMenu,MF_STRING,IDM_CLOSEALL,"Close All");
AppendMenu(hMenu,MF_STRING|MF_POPUP,(UINT)hSubMenu,"&Windows");
hSubMenu = CreatePopupMenu();
AppendMenu(hSubMenu,MF_STRING,IDM_ABOUT,"&About");
AppendMenu(hMenu,MF_STRING|MF_POPUP,(UINT)hSubMenu,"&Help");
if(hMenu == NULL){
MessageBox(NULL,"Menu Creation Failed!","Error!",MB_ICONEXCLAMATION);
return 0;
}
SetMenu(hwnd,hMenu); //setta il menu sulla finestra
//STEP 4: Message Loop
while(GetMessage(&msg,NULL,0,0) > 0){
if(hWndClient && TranslateMDISysAccel(hWndClient,&msg)) continue; //process the predefined MDI specific accelerator keys
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam;
}
To handle WM_SIZE in MDI frame, see documentation for DefFrameProc
WM_SIZE
Resizes the MDI client window to fit in the new frame window's client area. If the frame window procedure sizes the MDI client window to a different size, it should not pass the message to theDefWindowProcfunction.
If you are resizing the frame's client are, return zero. If you are not resizing then pass to DefWindowProc (not DefFrameProc)
To create a MDI child window, use MDICREATESTRUCT and SendMessage( ... WM_MDICREATE ... ), instead of CreateWindowEx(WS_EX_MDICHILD...
Suggestion to fix the procedure:
I am using a slightly different method to handle defaults. Also IDM_EXIT should call WM_CLOSE
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
static MDICREATESTRUCT mdicreate;
static HINSTANCE hinstance;
switch(msg)
{
case WM_CREATE:
{
hinstance = (HINSTANCE)GetWindowLong(hwnd, GWL_HINSTANCE);
CLIENTCREATESTRUCT ccs = { 0 };
ccs.hWindowMenu = GetSubMenu(GetMenu(hwnd), 1);
ccs.idFirstChild = IDM_FIRSTCHILD;
hWndClient = CreateWindow("MDICLIENT", "",
WS_CHILD | WS_CLIPCHILDREN | WS_VISIBLE,
0, 0, 0, 0, hwnd, NULL, 0, &ccs);
CreateWindow(STATUSCLASSNAME, NULL, WS_CHILD | WS_VISIBLE | SBARS_SIZEGRIP,
0, 0, 0, 0, hwnd, (HMENU)IDC_STATUSBAR, hinstance, NULL);
return 0;
}
case WM_SIZE:
{
RECT rc;
GetClientRect(hwnd, &rc);
int nHalf = rc.right / 2;
int nParts[4];
nParts[0] = nHalf;
nParts[1] = nHalf + nHalf / 3;
nParts[2] = nHalf + nHalf * 2 / 3;
nParts[3] = -1;
SendMessage(GetDlgItem(hwnd, IDC_STATUSBAR), SB_SETPARTS, 4, (LPARAM)&nParts);
SendMessage(GetDlgItem(hwnd, IDC_STATUSBAR), WM_SIZE, 0, 0);
RECT statusRect;
GetClientRect(GetDlgItem(hwnd, IDC_STATUSBAR), &statusRect);
rc.bottom -= statusRect.bottom;
MoveWindow(hWndClient, 0, 0, rc.right, rc.bottom, TRUE);
return 0;
}
case WM_DESTROY:
PostQuitMessage(0);
return 0;
case WM_COMMAND:
if(LOWORD(wParam) == IDM_EXIT)
{
SendMessage(hwnd, WM_CLOSE, 0, 0);
return 0;
}
if(LOWORD(wParam) == IDM_ABOUT)
MessageBox(hwnd, "ABOUT premuto", "ciao", MB_OK);
if(LOWORD(wParam) == IDM_OPEN)
{
mdicreate.szClass = childClass;
mdicreate.szTitle = "Title";
mdicreate.hOwner = hinstance;
mdicreate.x = CW_USEDEFAULT; //change this to a small number
mdicreate.y = CW_USEDEFAULT;
mdicreate.cx = CW_USEDEFAULT;
mdicreate.cy = CW_USEDEFAULT;
mdicreate.style = 0;
mdicreate.lParam = 0;
SendMessage(hWndClient, WM_MDICREATE, 0, (LPARAM)
(LPMDICREATESTRUCT)&mdicreate);
}
break;
}
return DefFrameProc(hwnd, hWndClient, msg, wParam, lParam);
}