信息發送格式如下所示
CRect rect;
GetClientRect(&rect);
PostMessage(WM_SIZE, (WPARAM)SIZE_RESTORED, MAKELPARAM(rect.Width(), rect.Height()));
//默認接收回調函數
void CMFCView::OnSize(UINT nType, int cx, int cy)
第一個參數就是系統消息WM_SIZE,這個是消息類型 窗口尺寸變動類型
第二個是參數是消息狀態 下圖是尺寸定義看名字便知功能
//FilePath:..\Windows Kits\10\Include\10.0.17763.0\um\WinUser.h Line:2635
/*
* WM_SIZE message wParam values
*/
#define SIZE_RESTORED 0
#define SIZE_MINIMIZED 1
#define SIZE_MAXIMIZED 2
#define SIZE_MAXSHOW 3
#define SIZE_MAXHIDE 4
第三個參數是窗口尺寸數據,他使用MAKELPARAM 宏將窗口尺寸int數據拼接成爲一個64位數據
可以在源碼庫中看到這樣的定義
//FilePath:..\Windows Kits\10\Include\10.0.17763.0\um\WinUser.h Line:1870
#define MAKELONG(a, b) ((LONG)(((WORD)(((DWORD_PTR)(a)) & 0xffff)) | ((DWORD)((WORD)(((DWORD_PTR)(b)) & 0xffff))) << 16))
#define MAKEWPARAM(l, h) ((WPARAM)(DWORD)MAKELONG(l, h))
#define MAKELPARAM(l, h) ((LPARAM)(DWORD)MAKELONG(l, h))
#define MAKELRESULT(l, h) ((LRESULT)(DWORD)MAKELONG(l, h))
消息分發處,原始結構見下
//FilePath:..\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\atlmfc\include\afxmsg_.h L:393
#define ON_WM_SIZE() \
{ WM_SIZE, 0, 0, 0, AfxSig_vwii, \
(AFX_PMSG)(AFX_PMSGW) \
(static_cast< void (AFX_MSG_CALL CWnd::*)(UINT, int, int) > ( &ThisClass :: OnSize)) },
其中 AfxSig_vwii = AfxSig_v_u_ii, // void (UINT, int, int) 標示了回調函數的參數類型
在源碼中wincore.cpp Line:2177 可以看到 WM_SIZE 是如何被處理的 以及2491行,消息是如何分發的
BOOL CWnd::OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult)
{
//...
switch (message)
{
case WM_SIZE:
{
ResizeDynamicLayout();
CHwndRenderTarget* pRenderTarget = GetRenderTarget();
if (pRenderTarget != NULL && pRenderTarget->IsValid())
{
pRenderTarget->Resize(CD2DSizeU(UINT32(LOWORD(lParam)), UINT32(HIWORD(lParam))));
RedrawWindow();
}
}
break;
//...
switch (lpEntry->nSig)
{
case AfxSig_v_u_ii:
(this->*mmf.pfn_v_u_i_i)(static_cast<UINT>(wParam), LOWORD(lParam), HIWORD(lParam));
break;
//..
}
據此根據數據的處理過程我們便清楚了 WM_SIZE的產生到處理的整個流程
PostMessage ->WindowProc->OnWndMsg ->OnSize