java - DragGestureEvent 的 startDrag 调用后 JTable 的列错位

Question

我已经实现了 JTableHeader 的拖放，因此当用户单击表头并按下 Ctrl 键而不是对列重新排序时，将传输自定义对象。

它看起来工作正常，但是当调用 DragGestureEvent 的 startDrag 方法时，被拖动的列变得不合适(请参阅第 4 列和第 5 列之间的间隙):

如果此后单击该列或在不使用 Ctrl 键的情况下拖动它，它将返回到正确的位置。有人知道如何让该列保持其位置吗？

源代码:

public class Tree {
    private final String name;

    public Tree (final String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "Tree[" + name + "]";
    };
}

还有这个:

import java.awt.BorderLayout;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DragGestureEvent;
import java.awt.dnd.DragGestureListener;
import java.awt.dnd.DragSource;
import java.awt.event.ActionEvent;
import java.awt.event.MouseEvent;
import java.io.IOException;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.SwingUtilities;
import javax.swing.TransferHandler;
import javax.swing.WindowConstants;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.JTableHeader;
import javax.swing.table.TableColumnModel;

public class DnDTest extends JPanel {

    private static final long serialVersionUID = 8341231933303004329L;

    private static final DataFlavor FLAVOR = new DataFlavor(Tree.class,
            Tree.class.getSimpleName());

    private final TableTransferHandler<Integer> customHandler = new TableTransferHandler<Integer>();

    /* ************** CONSTRUCTORS *************** */

    public DnDTest() {
        setLayout(new GridLayout(1, 2));
        final JTable table = createTable();
        table.setTableHeader(new CustomTableHeader(table.getColumnModel()));

        final JPanel right = new JPanel(new BorderLayout());
        final JLabel dropLabel = new JLabel();
        dropLabel.setTransferHandler(customHandler);
        right.add(dropLabel);
        this.add(right);

        new DragSource().createDefaultDragGestureRecognizer(
                table.getTableHeader(), DnDConstants.ACTION_COPY,
                new CustomDragGesture());
    }

    /* ************* PRIVATE METHODS ************* */

    private JTable createTable() {
        final DefaultTableModel model = createTableModel();
        final JTable table = new JTable(model);
        this.add(new JScrollPane(table));
        return table;
    }

    private DefaultTableModel createTableModel() {
        final String[] columnNames = { "Column1", //$NON-NLS-1$
                "Column2", //$NON-NLS-1$
                "Column3", //$NON-NLS-1$
                "Column4", //$NON-NLS-1$
                "Column5" //$NON-NLS-1$
        };
        final Integer[][] data = new Integer[1][columnNames.length];
        for (int i = 0; i < data.length; i++) {
            for (int j = 0; j < data[i].length; j++) {
                data[i][j] = (int) (Math.random() * 30);
            }
        }

        final DefaultTableModel model = new DefaultTableModel(data, columnNames);
        return model;
    }

    /* ***************** CLASSES ***************** */

    private static final class CustomTableHeader extends JTableHeader {

        private static final long serialVersionUID = -781646896813653894L;

        public CustomTableHeader(final TableColumnModel columnModel) {
            super(columnModel);
        }

        public Tree getTree() {
            return new Tree("Test tree");
        }
    }

    private static final class CustomDragGesture implements DragGestureListener {

        @Override
        public void dragGestureRecognized(DragGestureEvent event) {
            if (!(event.getTriggerEvent() instanceof MouseEvent && SwingUtilities
                    .isLeftMouseButton((MouseEvent) event.getTriggerEvent()))
                    || (event.getTriggerEvent().getModifiers() & ActionEvent.CTRL_MASK) != ActionEvent.CTRL_MASK)
                return;

            final CustomTableHeader tableHeader = (CustomTableHeader) event
                    .getComponent();

            Cursor cursor = null;
            if (event.getDragAction() == DnDConstants.ACTION_COPY) {
                cursor = DragSource.DefaultCopyDrop;
            }
            final Tree tree = tableHeader.getTree();

            event.startDrag(cursor, new TransferableTree(tree));
        }
    }

    private static final class TransferableTree extends Tree implements
            Transferable {

        private final Tree tree;

        public TransferableTree(final Tree tree) {
            super(tree.getName());
            this.tree = tree;
        }

        @Override
        public DataFlavor[] getTransferDataFlavors() {
            return new DataFlavor[] { FLAVOR };
        }

        @Override
        public boolean isDataFlavorSupported(DataFlavor flavor) {
            return FLAVOR.equals(flavor);
        }

        @Override
        public Object getTransferData(DataFlavor flavor)
                throws UnsupportedFlavorException, IOException {
            if (FLAVOR.equals(flavor)) {
                return tree;
            }
            throw new UnsupportedFlavorException(flavor);
        }

    }

    private static final class TableTransferHandler<T extends Number & Comparable<T>>
            extends TransferHandler {

        private static final long serialVersionUID = -1794178812912767711L;

        @Override
        public boolean importData(JComponent comp, Transferable t) {
            if (hasTreeFlavor(t.getTransferDataFlavors())) {
                try {
                    final Tree tree = (Tree) t.getTransferData(FLAVOR);
                    if (comp instanceof JLabel) {
                        final JLabel label = (JLabel) comp;
                        label.setText(label.getText() + tree.toString() + ", ");
                    }
                } catch (UnsupportedFlavorException | IOException e) {
                    e.printStackTrace();
                }
            }
            return false;
        }

        @Override
        public boolean canImport(JComponent comp, DataFlavor[] transferFlavors) {
            return hasTreeFlavor(transferFlavors);
        }

        private boolean hasTreeFlavor(DataFlavor[] transferDataFlavors) {
            for (final DataFlavor flavor : transferDataFlavors) {
                if (FLAVOR.equals(flavor)) {
                    return true;
                }
            }
            return false;
        }

    }

    public static void main(String[] args) {
        final JFrame frame = new JFrame("Drag And Drop Test");
        frame.add(new DnDTest());
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(1000, 800));
        frame.pack();
        frame.setVisible(true);
    }
}

任何想法将不胜感激。

Answer 1

在 dragGestureRecognized 的实现中，您可以调用 tableHeader.setDraggedDistance(0);

我对此进行了测试，它对我有用。