TreeTableView drag and drop

Question

I'm using a TreeTableView to display the content of a tree. The sorting order in the tree is manual, and I want to be able to drag and drop items.

How can I drag and drop items in a TreeTableView?

Answer 1

One way is to us a 'treeTableView.setRowFactory'. In the 'call' method, you create a row, to which you attach the 'onDragDetected', 'onDragDropped' etc. See example below.

// Create the root, RowContainer is your class contianing row attributes
TreeItem<RowContainer> rootTIFX = new TreeItem<RowContainer>(rowContainerRoot);

// Add leaves under your root.
...

// Create the row factory
treeTableView.setRowFactory(new Callback<TreeTableView, TreeTableRow<RowContainer>>() {
    @Override
    public TreeTableRow<RowContainer> call(final TreeTableView param) {
        final TreeTableRow<RowContainer> row = new TreeTableRow<RowContainer>();

        row.setOnDragDetected(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                // drag was detected, start drag-and-drop gesture
                TreeItem<RowContainer> selected = (TreeItem<RowContainer>) treeTableView.getSelectionModel().getSelectedItem();
                // to access your RowContainer use 'selected.getValue()'

                if (selected != null) {
                    Dragboard db = treeTableView.startDragAndDrop(TransferMode.ANY);

                    // create a miniature of the row you're dragging
                    db.setDragView(row.snapshot(null, null));

                    // Keep whats being dragged on the clipboard
                    ClipboardContent content = new ClipboardContent();
                    content.putString(selected.getValue().getName());
                    db.setContent(content);

                    event.consume();
                }
            }
        });
        row.setOnDragOver(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) {
                // data is dragged over the target
                Dragboard db = event.getDragboard();
                if (event.getDragboard().hasString()){
                    event.acceptTransferModes(TransferMode.MOVE);
                }
                event.consume();
            }});
        row.setOnDragDropped(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) {

                Dragboard db = event.getDragboard();
                boolean success = false;
                if (event.getDragboard().hasString()) {

                    if (!row.isEmpty()) {
                        // This is were you do your magic.
                        // Move your row in the tree etc 
                        // Here is two examples of how to access
                        // the drop destination:
                        int dropIndex = row.getIndex();
                        TreeItem<RowContainer> droppedon = row.getTreeItem();

                        success = true;
                    }
                }
                event.setDropCompleted(success);
                event.consume();
            }});
        return row;
    }
});