Processes drop event.
        
        :param      event | <QDropEvent>

def dropEvent( self, event ):
        """
        Processes drop event.
        
        :param      event | <QDropEvent>
        """
        if event.mimeData().hasUrls():
            url      = event.mimeData().urls()[0]
            filepath = url.toLocalFile()
            if filepath:
                self.setFilepath(filepath)