对话框回调函数的问题

#include<windows.h> #include"resource.h"   HWND hwnd_B; HINSTANCE g_hInstance;   //函数声明 LRESULT CALLBACK Proc_A(HWND, UINT, WPARAM, LPARAM); LRESULT CALLBACK Proc_B(HWND , UINT, WPARAM , LPARAM );   //主函数 int APIENTRY WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nShowCmd) {      g_hInstance = hInstance;      HWND hwnd_A = CreateDialog(g_hInstance,(LPCTSTR)(IDD_DIALOG_MAIN),NULL,(DLGPROC)Proc_A);           ::SetWindowPos(hwnd_A, HWND_TOP, 250,200,540, 310, SWP_SHOWWINDOW);      ::UpdateWindow(hwnd_A);           MSG msg;        if( NULL == hwnd_A )      {          ::MessageBox( NULL, "CreateWindow error", "error", MB_OK );          return -1;      }        while (GetMessage(&msg, NULL, 0, 0))      { TranslateMessage(&msg);          DispatchMessage(&msg);      }      return msg.wParam; }   //回调函数A LRESULT CALLBACK Proc_A(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam) {      switch (message)      {          case WM_INITDIALOG:               {                    return TRUE;               }          case WM_COMMAND:               {                    if (LOWORD(wParam) == IDOK)                    {                        hwnd_B = CreateDialogA( g_hInstance,                             (LPCTSTR)(IDD_DIALOG_STUDENT),                             hDlg,                             (DLGPROC)Proc_B);                        ::ShowWindow(hwnd_B,SW_SHOW);                        ::UpdateWindow(hwnd_B);                        return TRUE;                    }                    if (LOWORD(wParam) == IDCANCEL)                    {                        PostQuitMessage(0);                        return TRUE;                     }               }          case WM_DESTROY:               PostQuitMessage(0);      }     return FALSE; }   //回调函数B LRESULT CALLBACK Proc_B(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam) {      switch (message)      {          case WM_INITDIALOG:               {                    return TRUE;               }          case WM_COMMAND:               {                    if (LOWORD(wParam) == IDOK)                    {                        return TRUE;                    }                    if (LOWORD(wParam) == IDCANCEL)                    {                        EndDialog(hDlg, LOWORD(hwnd_B));                        return TRUE;                     }               }          case WM_DESTROY:               PostQuitMessage(0);      }     return FALSE; }

 

代码如上，令我不解的是最后一行的return FALSE 。

 

起初我不小心写成了return TRUE ，紧接着问题就来了，显示的子窗口只有按钮被绘制，其余部分都是原来屏幕的内容。

调用 ::UpdateWindow(hwnd_B); 问题依旧。

主窗口只能被拖动，不响应任何消息(我明明用的是非模态对话框)。子窗口的其他分支返回 TRUE 就可以，百思不得其解，究竟这个返回值意味着什么呢？windows在回调函数返回后干了些什么呢？希望有高手为我解惑。