WinAPI - C++ - How to completeley wipe/clear everything in window? - c++

Question

I am using WinAPI in C++ for my application. I have painted some text and drawn a bitmap in the window by handling the WM_PAINT message. I have also put some button controls in the window via the CreateWindow function by handling the WM_CREATE message. I have spent hours researching this but i've had no luck - How can I completely clear the window and all of it's content (what i've put in it), so i'm left with an empty window with the same background title, etc, so I can put more buttons and stuff on it.
Here's My Code
#include <windows.h>
#include <string>
#include "mainheader.h"
const char g_szClassName[] = "myWindowClass";
HBITMAP bitmap;
//Window Procedure #Brain of the Window
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam){
switch(msg){
case WM_CREATE:{
CreateWindow(TEXT("button"), TEXT("Play"),
WS_VISIBLE | WS_CHILD,
100, 227, 80, 25,
hwnd, (HMENU) 1, NULL, NULL);
CreateWindow(TEXT("button"), TEXT("Stats"),
WS_VISIBLE | WS_CHILD,
200, 227, 80, 25,
hwnd, (HMENU) 2, NULL, NULL);
CreateWindow(TEXT("button"), TEXT("Quit"),
WS_VISIBLE | WS_CHILD,
300, 227, 80, 25,
hwnd, (HMENU) 3, NULL, NULL);
bitmap = (HBITMAP) LoadImage(NULL, TEXT("menuIcon.bmp"), IMAGE_BITMAP, 130, 130, LR_LOADFROMFILE);
break;
}
case WM_COMMAND:{
switch(LOWORD(wParam)){
case 1:{
break;
}
case 2:{
break;
}
case 3:{
PostQuitMessage(0);
}
}
break;
}
case WM_PAINT:{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);
HDC hMemDC = CreateCompatibleDC(hdc);
::SelectObject(hMemDC, bitmap);
BitBlt(hdc, 170, 65, 200, 400, hMemDC, 0, 0, SRCCOPY);
::DeleteDC(hMemDC);
SetBkColor(hdc, RGB(0, 0, 0));
SetTextColor(hdc, RGB(0, 255, 0));
std::string text = "Welcome to Tic Tac Toe v2.0!";
std::string text2 = "Made By: Jaden Peterson (2015)";
std::string text3 = "Please choose an option below:";
TextOut(hdc, 150, 20, text.c_str(), text.length());
TextOut(hdc, 141, 45, text2.c_str(), text2.length());
TextOut(hdc, 145, 200, text3.c_str(), text3.length());
EndPaint(hwnd, &ps);
break;
}
case WM_CLOSE:{
DestroyWindow(hwnd);
break;
}
case WM_DESTROY:{
PostQuitMessage(0);
break;
}
default:{
return DefWindowProc(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 the Window Class
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = 0;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_MYICON));
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = CreateSolidBrush(RGB(0, 0, 0));
wc.lpszMenuName = NULL;
wc.lpszClassName = g_szClassName;
wc.hIconSm = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_MYICON));
if(!RegisterClassEx(&wc)){
MessageBox(NULL, "Window Registration Failed!", "Error!", MB_ICONEXCLAMATION | MB_OK);
return 0;
}
//Creating the Window
hwnd = CreateWindowEx(
WS_EX_CLIENTEDGE,
g_szClassName,
"Tic Tac Toe v2.0",
WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_MINIMIZEBOX,
CW_USEDEFAULT, CW_USEDEFAULT, 500, 300,
NULL, NULL, hInstance, NULL);
if(hwnd == NULL){
MessageBox(NULL, "Window Creation Failed!", "Error!", MB_ICONEXCLAMATION | MB_OK);
return 0;
}
ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);
//Message Loop #Heart of the Window
while(GetMessage(&Msg, NULL, 0, 0) > 0){
TranslateMessage(&Msg);
DispatchMessage(&Msg);
}
return Msg.wParam;
}

Answer 1

Deleting all child windows is simple. Do a loop and enum all the child windows using EnumChildWindows . For each returned handle, call DestroyWindow.
First declare the callback function:
BOOL CALLBACK DestoryChildCallback(
HWND hwnd,
LPARAM lParam
)
{
if (hwnd != NULL) {
DestroyWindow(hwnd)
}
return TRUE;
}
From your code:
EnumChildWindows(hwnd /* parent hwnd*/, DestoryChildCallback, NULL);