JavaFX帮助实现拖放

Question

What I am doing is creating an image view for each card in a deck of cards. For each image view, I add two events setOnDragOver and setOnDragDropped. However when I click and try to drag a card my print statement for the event doesn't even show.

What I am trying to do is allow for a card to be dragged on the pane. So change the position based on where I drag it but it still is on the window. Here are the events for the image view below.

        tempImageView.setOnDragOver(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) 
            {
                System.out.print("OnDragOver");
                Dragboard db = event.getDragboard();
                if (db.hasFiles()) 
                {
                    tempImage = card.getImage();
                    event.acceptTransferModes(TransferMode.ANY);
                }

                event.consume();
            }
        });

and this one is for drag dropped

        tempImageView.setOnDragDropped(new EventHandler<DragEvent>() 
        {
            @Override
            public void handle(DragEvent event) 
            {
                System.out.print("OnDragDropped");
                Dragboard dashboard = event.getDragboard();

                if (dashboard.hasFiles()) 
                {
                    for (File file : dashboard.getFiles()) 
                    {
                        String absolutePath = file.toURI().toString();

                        Image dashBoardImage = new Image(absolutePath);
                        ImageView dbImageView = new ImageView();
                        dbImageView.setFitHeight(screenHeight/19);
                        dbImageView.setFitWidth(screenWidth*0.0225);
                        dbImageView.setImage(tempImage);
                        root.getChildren().add(dbImageView);
                        //TODO this needs to be changed to place onto pain instead of using set fill
                        //rectangle.setFill(new ImagePattern(dashBoardImage, 0, 0, 1, 1, true));
                        root.getChildren().add(dbImageView);
                    }

                    event.setDropCompleted(true);
                } else {
                    event.setDropCompleted(false);
                }
                event.consume();

            }
        });

Answer 1

You need to implement EventHandler for OnDragDetected event. In this handler you need to call startDragAndDrop method on object, which will be dragged.

tempImageView.setOnDragDetected((event) -> {
    Image image;

    // Load your image and do other stuff.

    tempImageView.startDragAndDrop(TransferMode.ANY).setDragView(image);
});