java - 拖动时滚动表格

Question

我想要一个表作为放置目标，因为它实际上与删除项目的位置相关。因此，用户可能希望在开始拖动后重新调整可见项目。

我缺少的默认行为是:将鼠标悬停在最后一个可见行上并向下滚动表格。将鼠标悬停在第一条可见线上并向上滚动。

所以我现在正在做的是尝试将用户悬停的图标滚动到表格的中心:

    final Display display = new Display();
    final Shell shell = new Shell(display);
    shell.setLayout(new GridLayout());

    // drag source: the label

    final Label label = new Label(shell, SWT.NONE);
    label.setText("Drag from me!");
    label.setDragDetect(true);
    label.setLayoutData(GridDataFactory.fillDefaults().grab(true, false).create());

    final DragSource source = new DragSource(label, DND.DROP_MOVE | DND.DROP_COPY);
    source.setTransfer(new Transfer[]{TextTransfer.getInstance()});
    source.addDragListener(new DragSourceAdapter() {
        @Override
        public void dragSetData(DragSourceEvent event) {
            event.data = label.getText();
        }
    });

    // drop target: the viewer

    final TableViewer viewer = new TableViewer(shell,
            SWT.MULTI | SWT.H_SCROLL | SWT.V_SCROLL | SWT.FULL_SELECTION | SWT.BORDER);
    viewer.setContentProvider(ArrayContentProvider.getInstance());
    viewer.setLabelProvider(new ColumnLabelProvider());
    viewer.setInput(IntStream.range(1, 100).mapToObj(String::valueOf).collect(Collectors.toList()));
    viewer.getControl().setLayoutData(GridDataFactory.fillDefaults().grab(true, true).hint(100, 100).create());

    final DropTarget target = new DropTarget(viewer.getTable(), DND.DROP_MOVE | DND.DROP_COPY | DND.DROP_DEFAULT);
    target.setTransfer(new Transfer[]{TextTransfer.getInstance()});
    target.addDropListener(new DropTargetAdapter() {

        private static final int TIME_BETWEEN_MOVEMENTS = 700;
        private long lastMovementTime;

        @Override
        public void dragOver(DropTargetEvent event) {
            final Table table = viewer.getTable();
            final TableItem item = table.getItem(table.toControl(new Point(event.x, event.y)));
            if (item != null) {
                final long currentTime = System.currentTimeMillis();
                if (currentTime > this.lastMovementTime + TIME_BETWEEN_MOVEMENTS) {
                    table.setTopIndex(Math.max(0, table.indexOf(item) - getVisibleItems(table) / 2));
                    this.lastMovementTime = currentTime;
                }
                table.setSelection(item);
            }
        }

        private int getVisibleItems(Table table) {
            return (table.getClientArea().height - table.getHeaderHeight()) / table.getItemHeight();
        }
    });

    // open everything

    shell.pack();
    shell.open();

    while (!shell.isDisposed()) {
        if (!display.readAndDispatch()) {
            display.sleep();
        }
    }
    display.dispose();

这对于高 table 滚动很快，而不是小 table ，所以我想知道是否有更好的方法，因为这是我使用的大多数软件中非常常见的用例。

如何在拖动时滚动表格？

Answer 1

好吧，我进行了一些尝试，并提出了一个至少应该为您提供一个良好起点的解决方案。它的作用是监听各种鼠标事件并记住已选择的项目。当到达边缘(顶部或底部)时，它将把表格向上/向下移动一项。

private static boolean dragging = false;
private static int     start    = -1;
private static int     end      = -1;

public static void main(String[] args)
{
    final Display display = new Display();
    final Shell shell = new Shell(display);
    shell.setLayout(new FillLayout());

    List<String> input = IntStream.range(1, 100)
                                  .mapToObj(String::valueOf)
                                  .collect(Collectors.toList());

    final TableViewer viewer = new TableViewer(shell, SWT.MULTI | SWT.H_SCROLL | SWT.V_SCROLL | SWT.FULL_SELECTION | SWT.BORDER);
    viewer.setContentProvider(ArrayContentProvider.getInstance());
    viewer.setLabelProvider(new ColumnLabelProvider());
    viewer.setInput(input);

    Table table = viewer.getTable();
    // Stop dragging when the mouse is released
    table.addListener(SWT.MouseUp, e -> dragging = false);
    // Start dragging when the mouse is clicked
    table.addListener(SWT.MouseDown, e -> {
        dragging = true;
        start = -1;
        end = -1;
    });
    // Listen to mouse movement
    table.addListener(SWT.MouseMove, e -> {
        // If we're currently dragging
        if (dragging)
        {
            // Get the item under the mouse pointer
            TableItem item = table.getItem(new Point(e.x, e.y));

            if(item != null)
            {
                int current = table.indexOf(item);

                // If this is the first selected item, remember the position
                if (start == -1 && end == -1)
                {
                    start = current;
                    end = current;
                }
                // Else, just remember the "end" of the drag
                else
                    end = current;

                // Tell the viewer to select the items
                viewer.setSelection(new StructuredSelection(input.subList(Math.min(start, end), Math.max(start, end))));

                // Now, we actually move the table when the drag movement reaches the top or bottom
                int tableHeight = table.getClientArea().height;
                int itemHeight = table.getItemHeight();

                if (e.y < itemHeight && current > 0)
                    table.showItem(table.getItem(current - 1));
                else if (e.y > tableHeight - itemHeight && current < table.getItemCount() - 1)
                    table.showItem(table.getItem(current + 1));
            }
        }
    });

    shell.pack();
    shell.open();
    shell.setSize(400, 300);

    while (!shell.isDisposed())
    {
        if (!display.readAndDispatch())
        {
            display.sleep();
        }
    }
    display.dispose();
}