How to handle a button press (Desktop Application) - c++

Question

I am making a desktop application, and I got it to display a button. Now what I am trying to do is somehow handle the button press, but I do not know how. Here is my code so far:
#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <tchar.h>
// Global variables
// The main window class name.
static TCHAR szWindowClass[] = _T("DesktopApp");
// The string that appears in the application's title bar.
static TCHAR szTitle[] = _T("First Desktop Application");
HINSTANCE hInst;
// Forward declarations of functions included in this code module:
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
int CALLBACK WinMain(
_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPSTR lpCmdLine,
_In_ int nCmdShow
)
{
WNDCLASSEX wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wcex.lpszMenuName = NULL;
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, IDI_APPLICATION);
if (!RegisterClassEx(&wcex))
{
MessageBox(NULL,
_T("Call to RegisterClassEx failed!"),
_T("Windows Desktop Guided Tour"),
NULL);
return 1;
}
// Store instance handle in our global variable
hInst = hInstance;
// The parameters to CreateWindow explained:
// szWindowClass: the name of the application
// szTitle: the text that appears in the title bar
// WS_OVERLAPPEDWINDOW: the type of window to create
// CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
// 500, 100: initial size (width, length)
// NULL: the parent of this window
// NULL: this application does not have a menu bar
// hInstance: the first parameter from WinMain
// NULL: not used in this application
HWND hWnd = CreateWindow(
szWindowClass,
szTitle,
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT,
500, 500,
NULL,
NULL,
hInstance,
NULL
);
HWND hwndButton = CreateWindow(
L"BUTTON", // Predefined class; Unicode assumed
L"Test2", // Button text
WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON, // Styles
10, // x position
100, // y position
100, // Button width
20, // Button height
hWnd, // Parent window
NULL, // No menu.
(HINSTANCE)GetWindowLongPtr(hWnd, GWLP_HINSTANCE),
NULL);
if (!hWnd)
{
MessageBox(NULL,
_T("Call to CreateWindow failed!"),
_T("Windows Desktop Guided Tour"),
NULL);
return 1;
}
// The parameters to ShowWindow explained:
// hWnd: the value returned from CreateWindow
// nCmdShow: the fourth parameter from WinMain
ShowWindow(hWnd,
nCmdShow);
UpdateWindow(hWnd);
// Main message loop:
MSG msg;
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int)msg.wParam;
}
// FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// PURPOSE: Processes messages for the main window.
//
// WM_PAINT - Paint the main window
// WM_DESTROY - post a quit message and return
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
PAINTSTRUCT ps;
HDC hdc;
TCHAR greeting[] = _T("Test");
switch (message)
{
case WM_PAINT:
hdc = BeginPaint(hWnd, &ps);
// Here your application is laid out.
// For this introduction, we just print out "Hello, Windows desktop!"
// in the top left corner.
TextOut(hdc,
5, 5,
greeting, _tcslen(greeting));
// End application-specific layout section.
EndPaint(hWnd, &ps);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
break;
}
return 0;
}
It is a Windows Desktop Wizard project on Visual Studio 2019. I just want it to do something simple like display some text on the screen or something when the button is pressed.
This is what the window looks like:

Answer 1

When a BUTTON is clicked, it sends a BN_CLICKED notification message to its parent window. You would simply handle that message in your WndProc(), eg:
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
...
case WM_COMMAND:
{
if (HIWORD(wParam) == BN_CLICKED)
{
// LOWORD(wParam) is the button's ID
// HWND(lParam) is the button's HWND
// do something with them as needed...
return 0;
}
break;
}
...
}
return DefWindowProc(hWnd, message, wParam, lParam);
}
This is explained in the BUTTON documentation on MSDN:
Button Messages
Handling Messages from a Button
Notifications from a button are sent as either WM_COMMAND or WM_NOTIFY messages. Information about which message is used can be found on the reference page for each notification.
For more information on how to handle messages, see Control Messages. See also Button Messages.
Notification Messages from Buttons
When the user clicks a button, its state changes, and the button sends notification codes, in the form of WM_COMMAND messages, to its parent window. For example, a push button control sends the BN_CLICKED notification code whenever the user chooses the button. In all cases (except for BCN_HOTITEMCHANGE), the low-order word of the wParam parameter contains the control identifier, the high-order word of wParam contains the notification code, and the lParam parameter contains the control window handle.