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EnumWindows not finding hWnd from PID if program is started using QProcess

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  • hskoglundH hskoglund

    Hi, qpr->processId() and qpr->programId() are not the same, try changing programId to processId.

    W Offline
    W Offline
    Waoweens
    wrote on last edited by
    #4

    @hskoglund Sorry, that was a typo (I did not copy paste everything). But this typo does not exist on my actual program. I will edit my post

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    • Christian EhrlicherC Online
      Christian EhrlicherC Online
      Christian Ehrlicher
      Lifetime Qt Champion
      wrote on last edited by
      #5

      @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

      // this works
      EnumWindows(enumWindowCallback, 12345);
      // this does not work
      EnumWindows(enumWindowCallback, qpr->processId());

      Then check what qpr->processId() returns, also take a look in the TaskManager to see if you can find qpr->processId() there.

      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
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      • Christian EhrlicherC Christian Ehrlicher

        @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

        // this works
        EnumWindows(enumWindowCallback, 12345);
        // this does not work
        EnumWindows(enumWindowCallback, qpr->processId());

        Then check what qpr->processId() returns, also take a look in the TaskManager to see if you can find qpr->processId() there.

        W Offline
        W Offline
        Waoweens
        wrote on last edited by
        #6

        @Christian-Ehrlicher qpr->processId() returns 16228 and task manager also says 16228

        qDebug() << qpr->processId()
        

        12e67743-24f4-4c12-bb15-f101b1e2e3b9-image.png

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        • Christian EhrlicherC Online
          Christian EhrlicherC Online
          Christian Ehrlicher
          Lifetime Qt Champion
          wrote on last edited by Christian Ehrlicher
          #7

          @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

          GetWindowThreadProcessId

          So this doesn't seem to return what you're expecting. Don't think Qt and the task manager lies...

          See e.g. https://stackoverflow.com/questions/61246529/pid-returned-from-getwindowthreadprocessid-call-doesnt-match-the-pid-from-taskm

          Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
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          • Christian EhrlicherC Christian Ehrlicher

            @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

            GetWindowThreadProcessId

            So this doesn't seem to return what you're expecting. Don't think Qt and the task manager lies...

            See e.g. https://stackoverflow.com/questions/61246529/pid-returned-from-getwindowthreadprocessid-call-doesnt-match-the-pid-from-taskm

            W Offline
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            Waoweens
            wrote on last edited by
            #8

            @Christian-Ehrlicher I modified it to list every open window

            static BOOL CALLBACK enumWindowCallback(HWND hWnd, LPARAM lparam) {
                DWORD pid;
                GetWindowThreadProcessId(hWnd, &pid);
                qDebug() << hWnd << pid
                return TRUE;
            }
            //...
            EnumWindows(enumWindowCallback, 0);
            

            If the program is launched manually, it appears on the list.
            If the program is started with QProcess, it does not appear on the list.

            Christian EhrlicherC 1 Reply Last reply
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            • W Waoweens

              @Christian-Ehrlicher I modified it to list every open window

              static BOOL CALLBACK enumWindowCallback(HWND hWnd, LPARAM lparam) {
                  DWORD pid;
                  GetWindowThreadProcessId(hWnd, &pid);
                  qDebug() << hWnd << pid
                  return TRUE;
              }
              //...
              EnumWindows(enumWindowCallback, 0);
              

              If the program is launched manually, it appears on the list.
              If the program is started with QProcess, it does not appear on the list.

              Christian EhrlicherC Online
              Christian EhrlicherC Online
              Christian Ehrlicher
              Lifetime Qt Champion
              wrote on last edited by
              #9

              @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

              If the program is launched manually, it appears on the list.

              How do you know the PID in this case? Also from the task manager?

              Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
              Visit the Qt Academy at https://academy.qt.io/catalog

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              • hskoglundH Online
                hskoglundH Online
                hskoglund
                wrote on last edited by
                #10

                Hi, it could be that QProcess launches your program not as a top-level window but as a child, and then EnumWindows() never sees it :-(
                Perhaps QProcess startDetached() works better?

                Christian EhrlicherC 1 Reply Last reply
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                • hskoglundH hskoglund

                  Hi, it could be that QProcess launches your program not as a top-level window but as a child, and then EnumWindows() never sees it :-(
                  Perhaps QProcess startDetached() works better?

                  Christian EhrlicherC Online
                  Christian EhrlicherC Online
                  Christian Ehrlicher
                  Lifetime Qt Champion
                  wrote on last edited by
                  #11

                  @hskoglund said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                  Hi, it could be that QProcess launches your program not as a top-level window but as a child

                  How should it work otherwise - the Qt process is starting the process and therefore it's the creator. startDetached might work but must not.

                  The msdn documentation also tells which windows are evaluated: "Retrieves the identifier of the thread that created the specified window and, optionally, the identifier of the process that created the window."

                  Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
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                  • Christian EhrlicherC Christian Ehrlicher

                    @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                    If the program is launched manually, it appears on the list.

                    How do you know the PID in this case? Also from the task manager?

                    W Offline
                    W Offline
                    Waoweens
                    wrote on last edited by
                    #12

                    @Christian-Ehrlicher said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                    @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                    If the program is launched manually, it appears on the list.

                    How do you know the PID in this case? Also from the task manager?

                    Yes, task manager.

                    @hskoglund said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                    Hi, it could be that QProcess launches your program not as a top-level window but as a child, and then EnumWindows() never sees it :-(
                    Perhaps QProcess startDetached() works better?

                    using startDetached() makes processId() return 0.

                    Christian EhrlicherC 1 Reply Last reply
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                    • W Waoweens

                      @Christian-Ehrlicher said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                      @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                      If the program is launched manually, it appears on the list.

                      How do you know the PID in this case? Also from the task manager?

                      Yes, task manager.

                      @hskoglund said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                      Hi, it could be that QProcess launches your program not as a top-level window but as a child, and then EnumWindows() never sees it :-(
                      Perhaps QProcess startDetached() works better?

                      using startDetached() makes processId() return 0.

                      Christian EhrlicherC Online
                      Christian EhrlicherC Online
                      Christian Ehrlicher
                      Lifetime Qt Champion
                      wrote on last edited by
                      #13

                      @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                      using startDetached() makes processId() return 0.

                      As properly documented...

                      I don't understand the need at all for this.

                      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                      Visit the Qt Academy at https://academy.qt.io/catalog

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                      • Christian EhrlicherC Christian Ehrlicher

                        @Waoweens said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                        using startDetached() makes processId() return 0.

                        As properly documented...

                        I don't understand the need at all for this.

                        W Offline
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                        Waoweens
                        wrote on last edited by
                        #14

                        @Christian-Ehrlicher said in EnumWindows not finding hWnd from PID if program is started using QProcess:

                        I don't understand the need at all for this.

                        I want to embed an external program in a QWidget, but to do that you need the hWid of the program.

                        QWindow *embed = QWindow::fromWinId(hWid);
                        QWidget *widget = QWidget::createWindowContainer(embed)
                        
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                        • Christian EhrlicherC Online
                          Christian EhrlicherC Online
                          Christian Ehrlicher
                          Lifetime Qt Champion
                          wrote on last edited by
                          #15

                          Then you've to find another WinAPI function or modify the external program to return the winId to the caller.

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                          Visit the Qt Academy at https://academy.qt.io/catalog

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                          • W Offline
                            W Offline
                            Waoweens
                            wrote on last edited by
                            #16

                            Looks like adding a delay of 1 second makes it works, so maybe it was too fast?
                            But now the external program closes after 1 second. I removed qpr->terminate but now the QMainWindow wont start unless the external program is closed first.
                            Is there a way to make them both run at the same time?

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                            • W Offline
                              W Offline
                              Waoweens
                              wrote on last edited by
                              #17

                              Looks like using the QProcess::stateChanged signal (and removing terminate()) works.
                              It uses QThread::msleep() so its not ideal, but its fine for me.

                              HWND myHWND;
                              static BOOL CALLBACK enumWindowCallback(HWND hWnd, LPARAM lparam) {
                                  DWORD pid;
                                  GetWindowThreadProcessId(hWnd, &pid);
                              
                                  if (pid == lparam) {
                                      myHWND = hWnd;
                                      return FALSE;
                                  }
                                  return TRUE;
                              }
                              
                              ProgramStarter::ProgramStarter(QObject *parent)
                                  : QObject{parent}
                              {
                                  QProcess *qpr = new QProcess(this);
                              
                                  connect(qpr, &QProcess::stateChanged, this, [=](QProcess::ProcessState newState){
                                      if (newState == QProcess::Running) {
                                          QThread::msleep(250);
                                          EnumWindows(enumWindowCallback, qpr->processId());
                                      }
                                  });
                              
                                  QString executable = "C:\\path\\to\\program.exe";
                                  qpr->start(executable);
                              
                                  qDebug() << myHWND;
                              }
                              
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