(Qt user for 6 months, but this makes me realize I am still a newbie ...
Thank you in advance for your assistance.)

Environment:
Qt 4.1.0
Windows 2000 SP4
Microsoft VC 6.0

What is desired:
I am using the QtSingleApplication class to guarantee only one instance of an application
is running.

When a second instance is started, I want the original instance to become the application
of focus and the second instance to terminate.

What is observed:
The second instance terminates; however, the original instance does not gain
the input focus. The original instance's taskbar button usually flashes, but its
main window remains hidden behind other windows.

vRaiseWindowForThisInst() is being called because the window title is changed.

I have attempted to strip down the source files to the essentials ...

File main.h:
Qt Code: 
  1. extern  QtSingleApplication *  pApp;
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File main.cpp:
Qt Code: 
  1. QtSingleApplication *  pApp;
  2.  
  3. int  main( int  argc,  char *  argv  [] )
  4. {
  5.    pApp = new QtSingleApplication( "UniqueName", argc, argv );
  6.    if ( pApp->sendMessage( "RUNNING?" ) ) {
  7.       return  0;
  8.    }
  9.    pApp->initialize();
  10.  
  11.    pMain = new clMain();
  12.  
  13.    return  pApp->exec();
  14. }
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File clMain.h:
Qt Code: 
  1. class  clMain  : public QMainWindow
  2. {
  3.    Q_OBJECT
  4.  
  5.    public:
  6.       clMain( QWidget *  parent  = 0 );
  7.       virtual  ~clMain( void );
  8.  
  9.    private:
  10.       void  vRaiseWindowForThisInst( void );
  11.       void  customEvent( QEvent *  event );
  12.  
  13.    private slots:
  14.       void  vMessageReceivedFromOtherInst( const QString &  msg );
  15. };
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File clMain.cpp:
Qt Code: 
  1. clMain::clMain( QWidget *  parent )
  2.       : QMainWindow( parent )
  3. {
  4.    QPushButton *  pExitAllButton  = new QPushButton( "Exit All" );
  5.    setCentralWidget( pExitAllButton );
  6.  
  7.    connect( pExitAllButton, SIGNAL( clicked() ),
  8.             this,           SLOT( vExitAllPressed() ) );
  9.  
  10.    connect( pApp, SIGNAL( messageReceived( const QString & ) ),
  11.             this, SLOT( vMessageReceivedFromOtherInst( const QString & ) ) );
  12.  
  13.    setWindowTitle( "Original Title" );
  14.    show();
  15. }
  16.  
  17. clMain::~clMain( void )
  18. {
  19.    ;
  20. }
  21.  
  22. void  clMain::vRaiseWindowForThisInst( void )
  23. {
  24.    setWindowTitle( "CHANGED TITLE" );
  25.  
  26.    //setFocus( Qt::OtherFocusReason );
  27.    //show();
  28.    raise();
  29. }
  30.  
  31. enum  QEvent::Type  {
  32.    Event_Main_Raise  = QEvent::User +  1
  33. };
  34.  
  35. void  clMain::customEvent( QEvent *  event )
  36. {
  37.    switch ( event->type() ) {
  38.       default :
  39.          QMainWindow::customEvent( event );
  40.          break;
  41.  
  42.       case Event_Main_Raise :
  43.          vRaiseWindowForThisInst();
  44.          break;
  45.    }
  46. }
  47.  
  48. void  clMain::vMessageReceivedFromOtherInst( const QString &  msg )
  49. {
  50.    QApplication::postEvent( this, new QEvent( Event_Main_Raise ) );
  51. }
  52.  
  53. void  clMain::vExitAllPressed( void )
  54. {
  55.    close();
  56. }
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