Qt Code: 
  1. void MainWindow::dissolve( QWidget * pFadeOut, QWidget * pFadeIn )
  2. {
  3. 	QByteArray	opacityProp( QString( "windowOpacity" ).toLatin1() );
  4. 	QPropertyAnimation *  pFadeOutAnimation = new QPropertyAnimation( pFadeOut, opacityProp );
  5. 	QPropertyAnimation *  pFadeInAnimation  = new QPropertyAnimation( pFadeIn,  opacityProp );
  6.  
  7. 	int duration = 3000;
  8. 	pFadeOutAnimation->setDuration( duration );
  9. 	pDafeOutAnimation->setStartValue( 1.0 );
  10. 	pFadeOutAnimation->setEndValue( 0.0 );
  11.  
  12.         // Hide the fade out widget when the animation has stopped
  13. 	connect( pFadeOutAnimation, &QPropertyAnimation::finished, pFadeOut, &QWidget::hide );
  14.  
  15.         pFadeInAnimation->setDuration( duration );
  16. 	pFadeInAnimation->setStartValue( 0.0 );
  17. 	pFadeInAnimation->setEndValue( 1.0 );
  18.  
  19.         // Ensure the fade in widget is showing, but make it invisible by setting opacity to 0
  20. 	if ( !pFadeIn->isVisible() )
  21. 	{
  22. 		pFadeIn->setWindowOpacity( 0.0 );
  23. 		pFadeIn->show();
  24. 	}
  25.  
  26. 	pFadeOutAnimation->start( QAbstractAnimation::DeleteWhenStopped );
  27. 	pFadeInAnimation->start( QAbstractAnimation::DeleteWhenStopped );
  28. }
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Not tested, so may require some edits.