将行拖动到视口(viewport)之外时，JavaFX 自动向上或向下滚动表

Question

我有一个表格 View ，您可以拖动行来重新定位数据。问题是当在视口(viewport)中拖动记录上方或下方的行时，表格 View 会自动向上或向下滚动。

有什么想法可以在 JavaFX 中实现吗？

categoryProductsTable.setRowFactory(tv -> {

        TableRow<EasyCatalogueRow> row = new TableRow<EasyCatalogueRow>();

        row.setOnDragDetected(event -> {
            if (!row.isEmpty()) {
                Dragboard db = row.startDragAndDrop(TransferMode.MOVE);
                db.setDragView(row.snapshot(null, null));
                ClipboardContent cc = new ClipboardContent();
                cc.put(SERIALIZED_MIME_TYPE, new ArrayList<Integer>(categoryProductsTable.getSelectionModel().getSelectedIndices()));
                db.setContent(cc);
                event.consume();
            }
        });

        row.setOnDragOver(event -> {
            Dragboard db = event.getDragboard();
            if (db.hasContent(SERIALIZED_MIME_TYPE)) {
                event.acceptTransferModes(TransferMode.COPY_OR_MOVE);
                event.consume();

            }
        });

        row.setOnDragDropped(event -> {
            Dragboard db = event.getDragboard();
            if (db.hasContent(SERIALIZED_MIME_TYPE)) {
                int dropIndex;

                if (row.isEmpty()) {
                    dropIndex = categoryProductsTable.getItems().size();
                } else {
                    dropIndex = row.getIndex();
                }

                ArrayList<Integer> indexes = (ArrayList<Integer>) db.getContent(SERIALIZED_MIME_TYPE);

                for (int index : indexes) {
                    EasyCatalogueRow draggedProduct = categoryProductsTable.getItems().remove(index);
                    categoryProductsTable.getItems().add(dropIndex, draggedProduct);
                    dropIndex++;
                }

                event.setDropCompleted(true);
                categoryProductsTable.getSelectionModel().select(null);
                event.consume();

                updateSortIndicies();

            }
        });

        return row;
    });

Answer 1

好的，所以我想通了。不确定这是最好的方法，但它确实有效。基本上，我在处理 DragOver 事件的 TableView 中添加了一个事件监听器。在表格 View 中拖动行时会触发此事件。

本质上，在执行拖动时，我会确定我们是否需要向上或向下滚动或根本不滚动。这是通过确定被拖动的项目是否在表格 View 的上部或下部邻近区域内来完成的。

然后由 DragOver 事件监听器控制的单独线程处理滚动。

public class CategoryProductsReportController extends ReportController implements Initializable {

    @FXML
    private TableView<EasyCatalogueRow> categoryProductsTable;

    private ObservableList<EasyCatalogueRow> categoryProducts = FXCollections.observableArrayList();

    public enum ScrollMode {
        UP, DOWN, NONE
    }

    private AutoScrollableTableThread autoScrollThread = null;

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {

        initProductTable();

    }

    private void initProductTable() {

        categoryProductsTable.setItems(categoryProducts);
        ...

        ...

        // Multi Row Drag And Drop To Allow Items To Be Re-Positioned Within 
        // Table
        categoryProductsTable.setRowFactory(tv -> {

            TableRow<EasyCatalogueRow> row = new TableRow<EasyCatalogueRow>();

            row.setOnDragDetected(event -> {
                if (!row.isEmpty()) {
                    Dragboard db = row.startDragAndDrop(TransferMode.MOVE);
                    db.setDragView(row.snapshot(null, null));
                    ClipboardContent cc = new ClipboardContent();
                    cc.put(SERIALIZED_MIME_TYPE, new ArrayList<Integer>(categoryProductsTable.getSelectionModel().getSelectedIndices()));
                    db.setContent(cc);
                    event.consume();
                }
            });

            row.setOnDragOver(event -> {
                Dragboard db = event.getDragboard();
                if (db.hasContent(SERIALIZED_MIME_TYPE)) {
                    event.acceptTransferModes(TransferMode.COPY_OR_MOVE);
                    event.consume();

                }
            });

            row.setOnDragDropped(event -> {
                Dragboard db = event.getDragboard();
                if (db.hasContent(SERIALIZED_MIME_TYPE)) {
                    int dropIndex;

                    if (row.isEmpty()) {
                        dropIndex = categoryProductsTable.getItems().size();
                    } else {
                        dropIndex = row.getIndex();
                    }

                    ArrayList<Integer> indexes = (ArrayList<Integer>) db.getContent(SERIALIZED_MIME_TYPE);

                    for (int index : indexes) {
                        EasyCatalogueRow draggedProduct = categoryProductsTable.getItems().remove(index);
                        categoryProductsTable.getItems().add(dropIndex, draggedProduct);
                        dropIndex++;
                    }

                    event.setDropCompleted(true);
                    categoryProductsTable.getSelectionModel().select(null);
                    event.consume();

                    updateSortIndicies();

                }
            });

            return row;
        });

        categoryProductsTable.addEventFilter(DragEvent.DRAG_DROPPED, event -> {
            if (autoScrollThread != null) {
                autoScrollThread.stopScrolling();
                autoScrollThread = null;
            }
        });

        categoryProductsTable.addEventFilter(DragEvent.DRAG_OVER, event -> {

            double proximity = 100;

            Bounds tableBounds = categoryProductsTable.getLayoutBounds();

            double dragY = event.getY();

            //System.out.println(tableBounds.getMinY() + " --> " + tableBounds.getMaxY() + " --> " + dragY);
            // Area At Top Of Table View. i.e Initiate Upwards Auto Scroll If
            // We Detect Anything Being Dragged Above This Line.
            double topYProximity = tableBounds.getMinY() + proximity;

            // Area At Bottom Of Table View. i.e Initiate Downwards Auto Scroll If
            // We Detect Anything Being Dragged Below This Line.
            double bottomYProximity = tableBounds.getMaxY() - proximity;

            // We Now Make Use Of A Thread To Scroll The Table Up Or Down If
            // The Objects Being Dragged Are Within The Upper Or Lower
            // Proximity Areas
            if (dragY < topYProximity) {
                // We Need To Scroll Up
                if (autoScrollThread == null) {
                    autoScrollThread = new AutoScrollableTableThread(categoryProductsTable);
                    autoScrollThread.scrollUp();
                    autoScrollThread.start();
                }

            } else if (dragY > bottomYProximity) {
                // We Need To Scroll Down
                if (autoScrollThread == null) {
                    autoScrollThread = new AutoScrollableTableThread(categoryProductsTable);
                    autoScrollThread.scrollDown();
                    autoScrollThread.start();
                }

            } else {
                // No Auto Scroll Required We Are Within Bounds
                if (autoScrollThread != null) {
                    autoScrollThread.stopScrolling();
                    autoScrollThread = null;
                }
            }

        });

    }
}

class AutoScrollableTableThread extends Thread {

    private boolean running = true;
    private ScrollMode scrollMode = ScrollMode.NONE;
    private ScrollBar verticalScrollBar = null;

    public AutoScrollableTableThread(TableView tableView) {
        super();
        setDaemon(true);
        verticalScrollBar = (ScrollBar) tableView.lookup(".scroll-bar:vertical");

    }

    @Override
    public void run() {

        try {
            Thread.sleep(300);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }

        while (running) {

            Platform.runLater(() -> {
                if (verticalScrollBar != null && scrollMode == ScrollMode.UP) {
                    verticalScrollBar.setValue(verticalScrollBar.getValue() - 0.01);
                } else if (verticalScrollBar != null && scrollMode == ScrollMode.DOWN) {
                    verticalScrollBar.setValue(verticalScrollBar.getValue() + 0.01);
                }
            });

            try {
                sleep(50);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public void scrollUp() {
        System.out.println("Start To Scroll Up");
        scrollMode = ScrollMode.UP;
        running = true;
    }

    public void scrollDown() {
        System.out.println("Start To Scroll Down");
        scrollMode = ScrollMode.DOWN;
        running = true;
    }

    public void stopScrolling() {
        System.out.println("Stop Scrolling");
        running = false;
        scrollMode = ScrollMode.NONE;
    }

}