How to handle wrong drop location in JavaFx? - javafx

Question

In my GUI I create some dices (ImageView) and I can drag and drop them in one specific GridPane. When I drop a dice into the specific GridPane, the dice disappears from the initial location and it moves to the right position. This works fine only if I choose the right drop location.
The problem is how can I manage the wrong drop location?
Actually if I drop a dice in a wrong location (like outside the Gridpane) the dice disappears like it was moved to the right position.
I want to restore the dice to the original location if the dice isn't placed to the GridPane.
Is there a method can help me to check if I drop into the right location? Or something can prevent to drop into the wrong location?

Answer 1

You can check the transferMode property of the DragEvent passed to the onDragDone event:
dragSource.setOnDragDone(evt -> {
if (evt.getTransferMode() == null) {
System.out.println("drag aborted");
} else {
System.out.println("drag successfully completed");
}
});
Note: this requires you to mark the drag gesture as completed in the onDragDropped event handler using setDropCompleted. Example:
#Override
public void start(Stage primaryStage) {
Button source = new Button("Not dragged yet");
Button target = new Button("target");
HBox root = new HBox(20, source, target);
source.setOnDragDetected(evt -> {
Dragboard db = source.startDragAndDrop(TransferMode.COPY);
ClipboardContent content = new ClipboardContent();
content.putString(source.getText());
db.setContent(content);
});
source.setOnDragDone(evt -> {
source.setText(evt.getTransferMode() == null ? "failure" : "success");
});
target.setOnDragOver(evt -> {
if (evt.getDragboard().hasString()) {
evt.acceptTransferModes(TransferMode.COPY);
evt.consume();
}
});
target.setOnDragDropped(evt -> {
String value = evt.getDragboard().getString();
target.setText(value);
evt.setDropCompleted(true);
evt.consume();
});
Scene scene = new Scene(root);
primaryStage.setScene(scene);
primaryStage.show();
}