滚动 Table 拖动

Question

我想要一个 table 作为放置目标，如果它实际上与放置项目的位置相关。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：将鼠标悬停在最后可见的行上并向下滚动 table。将鼠标悬停在第一条可见行上并向上滚动。

所以我现在正在做的是尝试将用户悬停的图标滚动到 table 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 的人来说滚动很快，对于小的人则不然，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使用.

如何在拖动时滚动 table？

Answer 1

好的，我进行了一些试验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，它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 table up/down 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();
}

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