Java "Could Not Serialize the Data"

Question

I'm trying to get my clipboard to receive some custom data in a drag and drop. The custom data is another java type. This other type does implement serializable, so I'm really not sure why this isn't working. Any ideas are appreciated!

imgView.setOnDragDetected(new EventHandler<MouseEvent>() {
    public void handle(MouseEvent event) {
        ClipboardContent content = new ClipboardContent();
        content.put(dataFormat, RHSIconizedToken.this);
        Dragboard db = imgView.startDragAndDrop(TransferMode.ANY); 
        db.setContent(content); 
        event.consume();
    }
});

To retrieve this object later I'm using:

RHSIconizedToken replacementRHSiToken = (RHSIconizedToken) db.getContent(RHSIconizedToken.getDataFormat());

I'm getting the following error, but the RHSIconizedToken does implement Serializable

java.lang.IllegalArgumentException: Could not serialize the data

GetDataFormat returns the DataFormat Object that is used in the put argument in the first code example.

Answer 1

If your drag object isn't serializable, save it in a global variable during the drag. Here's a JavaFx (Java8 with lambdas) example with draggable tabs that go bewteen panes within the same JVM.

import java.util.Random;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.input.ClipboardContent;
import javafx.scene.input.DataFormat;
import javafx.scene.input.Dragboard;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;  

public class DraggingTabPane extends Application {  

    private static final DataFormat TAB_TYPE = new DataFormat("nonserializableObject/tab");
    private static Tab dndTab;// global for drag-n-drop of non-serializable type

    public static void main(String[] args) {  
        launch(args);  
    }  

    @Override  
    public void start(Stage primaryStage) {  
        TabPane tabPane1 = createDndTabPane();  
        TabPane tabPane2 = createDndTabPane();  
        VBox root = new VBox(10);  
        root.getChildren().addAll(tabPane1, tabPane2);  

        final Random rng = new Random();  
        for (int i=1; i<=8; i++) {  
            final Tab tab = createDraggableTab("Tab "+i);  
            final StackPane pane = new StackPane();  
            int red = rng.nextInt(256);  
            int green = rng.nextInt(256);  
            int blue = rng.nextInt(256);  
            String style = String.format("-fx-background-color: rgb(%d, %d, %d);", red, green, blue);  
            pane.setStyle(style);  
            final Label label = new Label("This is tab "+i);  
            label.setStyle(String.format("-fx-text-fill: rgb(%d, %d, %d);", 256-red, 256-green, 256-blue));  
            pane.getChildren().add(label);  
            pane.setMinWidth(600);  
            pane.setMinHeight(250);  
            tab.setContent(pane);  
            if (i<=4) {  
                tabPane1.getTabs().add(tab);  
            } else {  
                tabPane2.getTabs().add(tab);  
            }  
        }  

        primaryStage.setScene(new Scene(root, 600, 600));  
        primaryStage.show();  
    }  

    public TabPane createDndTabPane() {  
        final TabPane tabPane = new TabPane();  
        tabPane.setOnDragOver(event -> {  
            if (event.getDragboard().hasContent(TAB_TYPE) 
                    && dndTab.getTabPane() != tabPane) {// && different from source location  
                event.acceptTransferModes(TransferMode.MOVE);
                event.consume();  
            }  
        });  
        tabPane.setOnDragDropped(event -> {  
            if (event.getDragboard().hasContent(TAB_TYPE) 
                    && dndTab.getTabPane() != tabPane) {// && different from source location  
                dndTab.getTabPane().getTabs().remove(dndTab);  
                tabPane.getTabs().add(dndTab);  
                event.setDropCompleted(true);  
                event.consume();  
            }  
        });  
        return tabPane;  
    }  

    private Tab createDraggableTab(String text) {  
        final Tab tab = new Tab();  
        final Label label = new Label(text);  
        tab.setGraphic(label);  
        label.setOnDragDetected(event -> {  
            Dragboard dragboard = label.startDragAndDrop(TransferMode.MOVE);  
            ClipboardContent clipboardContent = new ClipboardContent();  
            clipboardContent.put(TAB_TYPE, 1);
            dndTab = tab;
            dragboard.setContent(clipboardContent);
            event.consume();
        });  
        return tab ;  
    }  
}

Answer 2

That's because your object is not serializable.

Indeed, it's not because it implements Serializable that it is Serializable.

Look deeper inside the exception, you might find something like this

Caused by: java.io.NotSerializableException: javafx.beans.property.SimpleObjectProperty

Maybe making some fields transient will help.