How to find the ListCell which is at the location of the drop position in javafx - javafx

Question

I have a ListView which is a dragdrop target. When handling OnDragDropped event, I would like to find the list cell which is at the position of the mouse. In addition I want to highlight items when mouse is hovered above them even during a drag drop operation. How can this be achieved in JavaFx.

Answer 1

Use a cell factory on the list view to define custom cells: that way you can register the drag handlers with the individual cells, instead of with the list view. Then it is easy for the drag handlers to know which cells have fired the event.
Here is a SSCCE:
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.control.TextField;
import javafx.scene.input.ClipboardContent;
import javafx.scene.input.Dragboard;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.BorderPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;
public class ListViewWithDragAndDrop extends Application {
#Override
public void start(Stage primaryStage) {
ListView<String> listView = new ListView<>();
listView.getItems().addAll("One", "Two", "Three", "Four");
listView.setCellFactory(lv -> {
ListCell<String> cell = new ListCell<String>() {
#Override
protected void updateItem(String item, boolean empty) {
super.updateItem(item, empty) ;
setText(item);
}
};
cell.setOnDragOver(e -> {
Dragboard db = e.getDragboard();
if (db.hasString()) {
e.acceptTransferModes(TransferMode.COPY);
}
});
cell.setOnDragDropped(e -> {
Dragboard db = e.getDragboard();
if (db.hasString()) {
String data = db.getString();
if (cell.isEmpty()) {
System.out.println("Drop on empty cell: append data");
listView.getItems().add(data);
} else {
System.out.println("Drop on "+cell.getItem()+": replace data");
int index = cell.getIndex();
listView.getItems().set(index, data);
}
e.setDropCompleted(true);
}
});
// highlight cells when drag target. In real life, use an external CSS file
// and CSS pseudoclasses....
cell.setOnDragEntered(e -> cell.setStyle("-fx-background-color: gold;"));
cell.setOnDragExited(e -> cell.setStyle(""));
return cell ;
});
TextField textField = new TextField();
textField.setPromptText("Type text and drag to list view");
textField.setOnDragDetected(e -> {
Dragboard db = textField.startDragAndDrop(TransferMode.COPY);
String data = textField.getText();
Text text = new Text(data);
db.setDragView(text.snapshot(null, null));
ClipboardContent cc = new ClipboardContent();
cc.putString(data);
db.setContent(cc);
});
BorderPane root = new BorderPane(listView, textField, null, null, null);
Scene scene = new Scene(root, 400, 400);
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}