java - SWT列表拖放: Get element at drop location

Question

您好，我有一个 SWT 列表，我希望能够通过拖放来更改列表中项目的顺序。 我有部分实现的代码。我不确定如何获取发生放置的元素，即获取释放拖动的项目的项目(以便我可以将其与拖动的项目交换)。 这是我到目前为止的代码:

    listComposite = new Composite(parent, SWT.NONE);
    documentList = new List(listComposite, SWT.BORDER | SWT.H_SCROLL | SWT.V_SCROLL);
    Transfer[] types = new Transfer[] { TextTransfer.getInstance() };
    DragSource source = new DragSource(documentList, DND.DROP_MOVE | DND.DROP_COPY);
    source.setTransfer(types);

    source.addDragListener(new DragSourceAdapter()
    {
        @Override
        public void dragSetData(DragSourceEvent event)
        {
            // Get the selected items in the drag source
            DragSource ds = (DragSource) event.widget;
            List list = (List) ds.getControl();
            String[] selection = list.getSelection();
            event.data = selection[0];
        }
    });
    DropTarget target = new DropTarget(documentList, DND.DROP_MOVE | DND.DROP_COPY
            | DND.DROP_DEFAULT);
    target.setTransfer(types);
    target.addDropListener(new DropTargetAdapter()
    {
        @Override
        public void dragEnter(DropTargetEvent event)
        {
            if (event.detail == DND.DROP_DEFAULT)
            {
                event.detail = (event.operations & DND.DROP_COPY) != 0 ? DND.DROP_COPY
                        : DND.DROP_NONE;
            }

            // Allow dropping text only
            for (int i = 0, n = event.dataTypes.length; i < n; i++)
            {
                if (TextTransfer.getInstance().isSupportedType(event.dataTypes[i]))
                {
                    event.currentDataType = event.dataTypes[i];
                }
            }
        }

        @Override
        public void dragOver(DropTargetEvent event)
        {
            event.feedback = DND.FEEDBACK_SELECT | DND.FEEDBACK_SCROLL;
        }

        @Override
        public void drop(DropTargetEvent event)
        {
            if (TextTransfer.getInstance().isSupportedType(event.currentDataType))
            {
                  //HELP: How to get the element were the drop occurs and swap it with the draged element.
            }
        }
    });

Answer 1

让这个东西发挥作用。可能不是最好的解决方案，但这就是我想出的。

@Override
        public void drop(DropTargetEvent event)
        {
            String sourceItemIndex = (String) event.data;
            String targetItemIndex = null;
            if (TextTransfer.getInstance().isSupportedType(event.currentDataType))
            {
                int dropYCordinate = event.y
                        - documentList.toDisplay(documentList.getLocation()).y;
                int itemTop = 0;
                // Search for the item index where the drop took place
                for (int i = 0; i < documentList.getItemCount(); i++)
                {

                    if (dropYCordinate >= itemTop
                            && dropYCordinate <= itemTop + documentList.getItemHeight())
                    {
                        targetItemIndex = documentList.getTopIndex() + i + "";
                    }
                    itemTop += documentList.getItemHeight();
                }
            }
            swapListItems(Integer.parseInt(sourceItemIndex), Integer.parseInt(targetItemIndex));
        }
    });

基本上，我获取了项目掉落点的 Y 坐标，并检查与该 Y 坐标重叠的项目。一旦获得目标，我所需要做的就是切换源和目标项。希望这可以帮助尝试做类似事情的人。