Made TreeView scrollable when dragged out, and some fixes

treedrag/DragAndScrollTreeView.java

@@ -0,0 +1,92 @@
+import javafx.animation.KeyFrame;
+import javafx.animation.Timeline;
+import javafx.geometry.Orientation;
+import javafx.scene.Node;
+import javafx.scene.control.ScrollBar;
+import javafx.scene.control.TreeItem;
+import javafx.scene.control.TreeView;
+import javafx.scene.input.DragEvent;
+import javafx.scene.input.ScrollEvent;
+import javafx.util.Duration;
+
+public class DragAndScrollTreeView<T> extends TreeView<T> {
+
+    private Timeline scrollTimeline = new Timeline();
+    private double scrollVelocity = 0;
+    private boolean dropped;
+
+    // Higher SCROLL_SPEED value = slower scroll.
+    private static final int SCROLL_SPEED = 100;
+    private static final int SCROLL_DURATION = 20;
+
+
+    public DragAndScrollTreeView(TreeItem<T> root) {
+        super(root);
+
+        setupScrolling();
+    }
+
+
+    private void setupScrolling () {
+        scrollTimeline.setCycleCount(Timeline.INDEFINITE);
+        scrollTimeline.getKeyFrames().add(new KeyFrame(Duration.millis(SCROLL_DURATION), (ActionEvent) -> dragScroll()));
+
+        setOnDragExited((DragEvent event) -> {
+
+            if (event.getY() > 0) {
+                scrollVelocity = 1.0 / SCROLL_SPEED;
+            }
+            else {
+                scrollVelocity = -1.0 / SCROLL_SPEED;
+            }
+            if (!dropped){
+                scrollTimeline.play();
+            }
+
+        });
+
+        setOnDragEntered(event -> {
+            scrollTimeline.stop();
+            dropped = false;
+        });
+
+        setOnDragDone(event -> {
+            scrollTimeline.stop();
+        });
+
+        setOnDragDropped((DragEvent event) ->{
+            scrollTimeline.stop();
+            event.setDropCompleted(true);
+            dropped = true;
+        });
+
+        setOnScroll((ScrollEvent event)-> {
+            scrollTimeline.stop();
+        });
+    }
+
+
+    private void dragScroll () {
+        ScrollBar sb = getVerticalScrollbar();
+        if (sb != null) {
+            double newValue = sb.getValue() + scrollVelocity;
+            newValue = Math.min(newValue, 1.0);
+            newValue = Math.max(newValue, 0.0);
+            sb.setValue(newValue);
+        }
+    }
+
+
+    private ScrollBar getVerticalScrollbar() {
+        ScrollBar result = null;
+        for (Node n : lookupAll(".scroll-bar")) {
+            if (n instanceof ScrollBar) {
+                ScrollBar bar = (ScrollBar) n;
+                if (bar.getOrientation().equals(Orientation.VERTICAL)) {
+                    result = bar;
+                }
+            }
+        }
+        return result;
+    }
+}

treedrag/TaskCellFactory.java

@@ -29,7 +29,7 @@ public TreeCell<TaskNode> call(TreeView<TaskNode> treeView) {
             @Override
             protected void updateItem(TaskNode item, boolean empty) {
                 super.updateItem(item, empty);
-                if (item == null) return;
+                if (item == null || empty) return;
 
                 ImageView iv1 = new ImageView();
                 if (item.getName().equals("Tasks")) {
@@ -86,7 +86,7 @@ private void dragOver(DragEvent event, TreeCell<TaskNode> treeCell, TreeView<Tas
 
     private void drop(DragEvent event, TreeCell<TaskNode> treeCell, TreeView<TaskNode> treeView) {
         Dragboard db = event.getDragboard();
-        boolean success = false;
+		event.setDropCompleted(false);
         if (!db.hasContent(JAVA_FORMAT)) return;
 
         TreeItem<TaskNode> thisItem = treeCell.getTreeItem();
@@ -106,7 +106,7 @@ private void drop(DragEvent event, TreeCell<TaskNode> treeCell, TreeView<TaskNod
             thisItem.getParent().getChildren().add(indexInParent + 1, draggedItem);
         }
         treeView.getSelectionModel().select(draggedItem);
-        event.setDropCompleted(success);
+        event.setDropCompleted(true);
     }
 
     private void clearDropLocation() {

treedrag/TreeDragDemo.java

@@ -29,7 +29,7 @@ public void start(Stage primaryStage) {
         children.add(new TreeItem<TaskNode>(new TaskNode("walk dog")));
         children.add(new TreeItem<TaskNode>(new TaskNode("buy beer")));
 
-        TreeView<TaskNode> tree = new TreeView<TaskNode>(rootItem);
+        DragAndScrollTreeView<TaskNode> tree = new DragAndScrollTreeView<TaskNode>(rootItem);
         tree.setCellFactory(new TaskCellFactory());
 
         StackPane root = new StackPane();