MessageBox doesn't appear - c++

Question

I code in codeblocks.
Compiler = gcc version 4.9.2 (tdm-1)
I call MessageBox in WM_COMMAND.
When I press the button, The main window stop, But the MessageBox does not show.
I'm sure the WindowProc receive the button event!
But if I create a thread, and call MessageBox in the thread function, the MessageBox will show when I press the button. But if I call MessageBox in thread, Then then MessageBox can`t stop the main window.
How I can solve this problem?
#define IDI_BUTTON_1 10001
#define IDI_BUTTON_2 10002
#ifndef UNICODE
#define UNICODE
#endif
#include "resource.h"
#include "main.h"
#include <windows.h>
#include <stdio.h>
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, LPSTR pCmdLine, int nCmdShow)
{
// Register the window class.
const wchar_t CLASS_NAME[] = L"mywindow";
WNDCLASS wc = { };
wc.lpfnWndProc = WindowProc;
wc.hInstance = hInstance;
wc.lpszClassName = CLASS_NAME;
wc.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_MYICON));
//wc.style = CS_HREDRAW|CS_VREDRAW;
RegisterClass(&wc);
// Create the window.
HWND hwnd = CreateWindow( CLASS_NAME,
L"Mywindow",
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT,
CW_USEDEFAULT,
250,
200,
NULL,
NULL,
hInstance,
NULL
);
if (hwnd == NULL)
{
return 0;
}
ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);
// Run the message loop.
MSG msg = { };
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
int i;
switch (uMsg)
{
case WM_DESTROY:
PostQuitMessage(0);
return 0;
case WM_CREATE:
{
HWND hwndButton1 = CreateWindow( L"button" ,L"button1",
WS_CHILD|WS_VISIBLE,
10,
10,
75,
50,
hwnd,
(HMENU)IDI_BUTTON_1,
((LPCREATESTRUCT)lParam)->hInstance,
NULL);
HWND hwndButton2 = CreateWindow( L"button" ,L"button2",
WS_CHILD|WS_VISIBLE,
120,
10,
75,
50,
hwnd,
(HMENU)IDI_BUTTON_2,
((LPCREATESTRUCT)lParam)->hInstance,
NULL);
return 0;
}
case WM_COMMAND:
{
switch (LOWORD(wParam))
{
case IDI_BUTTON_1:
MessageBoxW( hwnd, L"button1", L"button1", MB_ICONERROR|MB_DEFAULT_DESKTOP_ONLY );
break;
case IDI_BUTTON_2:
MessageBoxW( hwnd, L"button2", L"button2", MB_ICONERROR|MB_DEFAULT_DESKTOP_ONLY );
break;
}
return 0;
}
case WM_PAINT:
{
return 0;
}
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}