How to get main window handle from process id

Question

How to get main window handle from process id   I want to bring this window to the front   It works well in  Process Explorer

User · Answer

Just to make sure you are not confusing the tid  thread id  and the pid  process id    DWORD pid  DWORD tid   GetWindowThreadProcessId  this- gt m hWnd   amp pid

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There s the possibility of a mis-understanding here   The WinForms framework in  Net automatically designates the first window created  e g   Application Run new SomeForm     as the MainWindow   The win32 API  however  doesn t recognize the idea of a  main window  per process   The message loop is entirely capable of handling as many  main  windows as system and process resources will let you create   So  your process doesn t have a  main window    The best you can do in the general case is use EnumWindows   to get all the non-child windows active on a given process and try to use some heuristics to figure out which one is the one you want   Luckily  most processes are only likely to have a single  main  window running most of the time  so you should get good results in most cases

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I checked how  NET determines the main window   My finding showed that it also uses EnumWindows     This code should do it similarly to the  NET way   struct handle data       unsigned long process id      HWND window handle      HWND find main window unsigned long process id        handle data data      data process id   process id      data window handle   0      EnumWindows enum windows callback   LPARAM  amp data       return data window handle     BOOL CALLBACK enum windows callback HWND handle  LPARAM lParam        handle data amp  data     handle data  lParam      unsigned long process id   0      GetWindowThreadProcessId handle   amp process id       if  data process id    process id     is main window handle           return TRUE      data window handle   handle      return FALSE        BOOL is main window HWND handle           return GetWindow handle  GW OWNER      HWND 0  amp  amp  IsWindowVisible handle

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Though it may be unrelated to your question  take a look at GetGUIThreadInfo Function

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As an extension to Hiale s solution  you could provide a different or modified version that supports processes that have multiple main windows   First  amend the structure to allow storing of multiple handles   struct handle data       unsigned long process id      std  vector lt HWND gt  handles       Second  amend the callback function   BOOL CALLBACK enum windows callback HWND handle  LPARAM lParam        handle data amp  data     handle data  lParam      unsigned long process id   0      GetWindowThreadProcessId handle   amp process id       if  data process id    process id     is main window handle             return TRUE               change these 2 lines to allow storing of handle and loop again     data handles push back handle       return TRUE          Finally  amend the returns on the main function   std  vector lt HWD gt  find main window unsigned long process id        handle data data      data process id   process id      EnumWindows enum windows callback   LPARAM  amp data       return data handles

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Here  I would like to add that if you are reading window handle that is HWND of a process then that process should not be running in a debugging otherwise it will not find the window handle by using FindWindowEx

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I don t believe Windows  as opposed to  NET  provides a direct way to get that   The only way I know of is to enumerate all the top level windows with EnumWindows   and then find what process each belongs to GetWindowThreadProcessID    This sounds indirect and inefficient  but it s not as bad as you might expect -- in a typical case  you might have a dozen top level windows to walk through

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This is my solution using pure Win32 C   based on the top answer   The idea is to wrap everything required into one function without the need for external callback functions or structures    include  lt utility gt   HWND FindTopWindow DWORD pid        std  pair lt HWND  DWORD gt  params     0  pid            Enumerate the windows using a lambda to process each window     BOOL bResult   EnumWindows    HWND hwnd  LPARAM lParam  - gt  BOOL                auto pParams    std  pair lt HWND  DWORD gt    lParam            DWORD processId          if  GetWindowThreadProcessId hwnd   amp processId   amp  amp  processId    pParams- gt second                           Stop enumerating             SetLastError -1               pParams- gt first   hwnd              return FALSE                        Continue enumerating         return TRUE          LPARAM  amp params        if   bResult  amp  amp  GetLastError      -1  amp  amp  params first                return params first             return 0

User · Answer

Old question but appears to have a lot of traffic  here is a simple solution  IntPtr GetMainWindowHandle IntPtr aHandle            return System Diagnostics Process GetProcessById aHandle ToInt32    MainWindowHandle

[c++] How to get main window handle from process id?

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