I've code this below and works. When I selected (only one click) a fileName in myFileDialog, on the right, in the preview box appear if the file selected is a pixmap or not; I'd like, when I click, show in preview box, the preview of image (the image). How to do? Thanks
Qt Code: 
  1. class Preview : public QLabel, public QFilePreview {
  2. public:
  3.     Preview( QWidget *parent=0 ) : QLabel( parent ) {}
  4.  
  5.     void previewUrl( const QUrl &u )
  6.     {
  7.         QString path = u.path();
  8.         QPixmap pix( path );
  9. 		if ( pix.isNull() ) {			
  10.             setText( "This is not a pixmap" );
  11. 		} else {
  12.  
  13.             setText( "This is a pixmap" );
  14. 		}
  15.     }
  16. };
  17.  
  18. Preview* p = new Preview;
  19. myFileDialog* myFd = new myFileDialog(this,"",)
  20. myFd->setContentsPreviewEnabled( TRUE );
  21. myFd->setContentsPreview( p, p );
  22.  if ( myFd->exec() == QDialog::Accepted )
  23.         file = myFd->selectedFile();
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