nswindow subclass macruby drag file to open ...hours for this quite simple solution

dragwidnow.rb

class DragWindow < NSWindow
    
    def awakeFromNib
        self.registerForDraggedTypes [NSFilenamesPboardType]
    end
        
    def performDragOperation(sender)
        filenames = sender.draggingPasteboard.propertyListForType(NSFilenamesPboardType)
        
        p filenames.inspect
        
        return NSApp.delegate.openFile(filenames.first) unless filenames.count == 0
        false
    end
    
    def draggingEntered(sender)
        p 'drag entered'
        NSDragOperationCopy
    end

end