C++程序利用Windows API獲取GUI程序的主窗口

首先要根據進程名稱獲取進程的pid：

int ProcessUtilities::lookupProcesses(const std::string &procName, std::vector<PROCESSENTRY32> &pes)
{
   string lowProcName = procName;
   StringUtility::lower(lowProcName);
   vector<PROCESSENTRY32> totalEntries;
   int errorCode = snapshotProcesses(totalEntries);
   if (errorCode == NO_ERROR)
   {
      pes.clear();
      for(const PROCESSENTRY32& entry : totalEntries)
      {
         string execName = entry.szExeFile;
         StringUtility::lower(execName);
         if (lowProcName.compare(execName) == 0)
         {
            pes.push_back(entry);
         }
      }
   }
   return errorCode;
}

int ProcessUtilities::getPids(const std::string &procName, std::vector<DWORD> &pids)
{
   vector<PROCESSENTRY32> entries;
   int errorCode = lookupProcesses(procName, entries);
   if (errorCode == NO_ERROR)
   {
      for(PROCESSENTRY32 entry : entries)
      {
         pids.push_back(entry.th32ProcessID);
      }
   }
   return errorCode;
}

上述代碼裏之所以用vector來存放pid，是因爲同名進程可能會有多個實例，每個實例會有自己的pid，需要找出進程的所有實例。

找到進程的所有實例pid之後，對每個pid，找到其所有的窗口：

struct WindowInformation
{
   public:
      HWND handle;
      HWND parent;
      HWND owner;
      LONG style;
      DWORD pid;  // process id
      DWORD tid;  // creator thread id
      char title[MAX_TITLE_LENGTH];
      char cls[MAX_CLASS_LENGTH];      // window class name.

   public:
      std::string& toString(int level = 0);

   private:
      std::string text;
};

struct WindowTree
{
   public:
      WindowInformation info;
      std::vector<WindowTree> children;

   public:
      std::string& toString(int level = 0);

   private:
      std::string text;
};

void WindowUtilities::getWindowInformation(const HWND hWnd, WindowUtilities::WindowInformation& windInfo)
{
   windInfo.handle = hWnd;
   windInfo.parent = GetParent(hWnd);
   windInfo.owner = GetWindow(hWnd, GW_OWNER);
   windInfo.style = GetWindowLong(hWnd, GWL_STYLE);
   GetWindowText(hWnd, windInfo.title, WindowUtilities::MAX_TITLE_LENGTH);
   GetClassName(hWnd, windInfo.cls, WindowUtilities::MAX_CLASS_LENGTH);
   windInfo.tid = GetWindowThreadProcessId(hWnd, &windInfo.pid);
}

bool WindowUtilities::enumMainWndProc(const HWND hWnd, LPARAM lParam)
{
   WindowInformation wi = getWindowInformation(hWnd);
   vector<WindowInformation> *wis = (vector<WindowInformation> *)lParam;
   if (isMainWindow(hWnd))
   {
      (*wis).push_back(wi);
   }
   return true;
}

int WindowUtilities::getWindows(WindowTree& windTree)
{
   getWindowInformation(GetDesktopWindow(), windTree.info);
   EnumWindows((WNDENUMPROC)enumWindowsProc, (LPARAM)(&windTree));

   return NO_ERROR;
}

int WindowUtilities::filterWindows(WindowUtilities::WindowTree& totalTree, DWORD pid, vector<WindowUtilities::WindowTree>& windTree)
{
   if (totalTree.info.pid == pid)
   {
      windTree.push_back(totalTree);
   }
   else
   {
      for(WindowUtilities::WindowTree wt : totalTree.children)
      {
         filterWindows(wt, pid, windTree);
      }
   }

   return windTree.size();
}

int WindowUtilities::getWindows(DWORD pid, vector<WindowUtilities::WindowTree>& windTree)
{
   WindowTree totalTree;
   getWindows(totalTree);
   filterWindows(totalTree, pid, windTree);
   return 0;
}

int WindowUtilities::getWindows(DWORD pid, std::vector<HWND> &hWnds)
{
   vector<WindowUtilities::WindowTree> wts;
   getWindows(pid, wts);
   hWnds.clear();
   for(WindowUtilities::WindowTree& wt : wts)
   {
      hWnds.push_back(wt.info.handle);
   }
   return 0;
}

最後，從pid的所有窗口中過濾出主窗口。主窗口的標誌是：窗口有標題，窗口style爲WS_VISIBLE，窗口無owner。代碼如下：

bool WindowUtilities::isMainWindow(HWND hWnd)
{
   WindowInformation windInfo = getWindowInformation(hWnd);
   DWORD visibleStyle = WS_VISIBLE;
   bool result = (((string(windInfo.title).length() != 0) && (windInfo.style & (visibleStyle)) != 0) && (windInfo.owner == nullptr)) ? true : false;
   return result;
}

int WindowUtilities::getMainWindows(DWORD pid, std::vector<HWND> &hWnds)
{
   vector<HWND> totalWindows;
   getWindows(pid, totalWindows);
   for(HWND hWnd : totalWindows)
   {
      if (isMainWindow(hWnd))
      {
         hWnds.push_back(hWnd);
      }
   }
   return 0;
}