Thread: How to clear the window content and print new content ?

Hi,

I'm trying to develop a simple program to do the following:

1. Develop main menu, then list some buttons and each button print a content.
2. There should be a 'main_menu' button on page1 and page2 to get me back to the 'main_menu'.

The problem is that when I press the 'main_menu' button, I get content from page1 and page2 on the 'main_menu' page.

I just need to know how to clear the window and print new content.


Here's my code:

Code:

#include <windows.h>
#include <stdint.h>

#define FILE_MENU_NEW   1   // File menu item to be used as window numbered functions
#define FILE_MENU_OPEN  2   // File menu item to be used as window numbered functions
#define FILE_MENU_EXIT  3   // File menu item to be used as window numbered functions

#define HOME_PAGE       4
#define PAGE1           5
#define PAGE2           6

LRESULT CALLBACK WindowProcedure(HWND, UINT, WPARAM, LPARAM);
void main_page(HWND hWnd);
void page1(HWND hWnd);
void page2(HWND hWnd);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR args, int nCmdShow){

    WNDCLASSW wc = {0};

    wc.hbrBackground = (HBRUSH)COLOR_WINDOW;    // color of the window
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);   // shape of the cursor
    wc.hInstance = hInstance;                   // pass it windows main system handler
    wc.lpszClassName = L"myWindowClass";        // name of the window class
    wc.lpfnWndProc = WindowProcedure;

    if(!RegisterClassW(&wc)){
        return -1;
    }

    CreateWindowW(L"myWindowClass", L"My Window", WS_OVERLAPPEDWINDOW | WS_VISIBLE, 1920/4, 1080/8, 320, 480,
        NULL,       // Parent window
        NULL,       // Menu
        NULL,       // Instance handle
        NULL        // Additional application data
        );

    MSG msg = {0};

    while(GetMessage(&msg, NULL, (uint64_t)NULL, (uint64_t)NULL)){
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

LRESULT CALLBACK WindowProcedure(HWND hWnd, UINT msg, WPARAM wp, LPARAM lp){
    switch(msg){

    case WM_COMMAND:
        switch(wp){

        case FILE_MENU_NEW:
            MessageBeep(MB_ICONINFORMATION);
            break;
        case FILE_MENU_OPEN:
            MessageBeep(MB_OK);
            break;
        case FILE_MENU_EXIT:
            break;

        case HOME_PAGE:
            main_page(hWnd);
            break;

        case PAGE1:
            page1(hWnd);
            break;
        case PAGE2:
            page2(hWnd);
            break;
        }

        break;

    case WM_CREATE:
        main_page(hWnd);
        break;

    case WM_DESTROY:
        PostQuitMessage(0);
        break;

    case WM_QUIT:
        break;

    default:
        return DefWindowProcW(hWnd, msg, wp, lp);

    }
    return 0;
}

void main_page(HWND hWnd){
    CreateWindowW(L"Static", L"main page", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 10, 180, 20, hWnd, NULL, NULL, NULL);

    CreateWindowW(L"Button", L"Page1", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 50, 180, 30, hWnd, (HMENU)PAGE1, NULL, NULL);
    CreateWindowW(L"Button", L"Page2", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 90, 180, 30, hWnd, (HMENU)PAGE2, NULL, NULL);
}

void page1(HWND hWnd){
    CreateWindowW(L"Static", L"Page1", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 10, 180, 20, hWnd, NULL, NULL, NULL);

    CreateWindowW(L"Button", L"P1 - button1", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 50, 180, 30, hWnd, NULL, NULL, NULL);
    CreateWindowW(L"Button", L"P1 - button2", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 90, 180, 30, hWnd, NULL, NULL, NULL);
    CreateWindowW(L"Button", L"P1 - button3", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 130, 180, 30, hWnd, NULL, NULL, NULL);

    CreateWindowW(L"Button", L"Main Page - P1", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 310, 180, 30, hWnd, (HMENU)HOME_PAGE, NULL, NULL);
}

void page2(HWND hWnd){
    CreateWindowW(L"Static", L"Page2", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 10, 180, 20, hWnd, NULL, NULL, NULL);

    CreateWindowW(L"Button", L"P2 - button1", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 50, 180, 30, hWnd, NULL, NULL, NULL);
    CreateWindowW(L"Button", L"P2 - button2", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 90, 180, 30, hWnd, NULL, NULL, NULL);
    CreateWindowW(L"Button", L"P2 - button3", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 130, 180, 30, hWnd, NULL, NULL, NULL);

    CreateWindowW(L"Button", L"Main Page - P2", WS_VISIBLE | WS_CHILD | WS_BORDER | SS_CENTER
                  , 65, 310, 180, 30, hWnd, (HMENU)HOME_PAGE, NULL, NULL);
}

I haven't used windows in forever, but if I remember correctly, a properly-designed window procedure has a WM_PAINT event to draw the window, and a function called InvalidateRect is used to "clear the screen" and redraw the window.
So something like this:

Code:

LRESULT CALLBACK WindowProcedure(HWND hWnd, UINT msg, WPARAM wp, LPARAM lp) {
 
    static int current_page = 0;
 
    switch (msg) {
 
    case WM_COMMAND:
        switch(wp){
 
        ...
 
        case HOME_PAGE:
            current_page = 0;
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        case PAGE1:
            current_page = 1;
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        case PAGE2:
            current_page = 2;
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        }
        break;
 
    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);


            switch (current_page) {
            case 0:
                main_page(hwnd);
                break;
            case 1:
                page1(hwnd);
                break;
            case 2:
                page2(hwnd);
                break;
            }
            EndPaint(hwnd, &ps);
        }
        break;
     ...
 
    }
}

It shows. That's horrendous advice

I realized it wasn't a good idea after I posted that it since it would cause the windows to be created over and over again. I thought of tabs but couldn't remember anything about how it was done.