问题描述

最近我解决了当 DnD 项目从 JList 到 JTable 对象时得到的神秘"IOException.显然，我传输的对象必须是可序列化的.这是必须"，还是有办法避免序列化?

Recently I solved a "mysterious" IOException that I got while DnD items from a JList to the JTable objects. Apparently objects that I transfer must be serializable. Is this "a must", or there is a way to avoid serialization?

我必须注意的一件事 - 我要转移的类型在不同的包中.

One thing I must note - the type I am transferring is in a different package.

推荐答案

你可以写一个自定义的TransferHandler.例如，我相信 JTabel 的 TranferHandler 将导出一个以逗号分隔的字符串，然后导入将解析该字符串以将每个标记添加为不同的列.

You can write a custom TransferHandler. For example I believe a TranferHandler for a JTabel will export a String that is comma delimited and then the import will parse the string to add each token as a different column.

因此，在您的情况下，您可以以相同的方式导出数据.然后在您导入时，您需要能够使用已解析的标记重新创建您的自定义对象.

So in your case you could export you data the same way. Then on you import you would need to be able to recreate your custom Object using the parsed tokens.

查看 拖放和数据传输上的 Swing 教程 了解更多信息和示例.

Take a look at the Swing tutorial on Drag and Drop and Data Transfer for more information and examples.

或者，如果 DnD 仅在您的 Java 应用程序之间，则可能比您传递对对象的实际引用更容易.这是我尝试通过在面板之间拖动 Swing 组件来执行此类操作的示例:

Or maybe easier if the DnD is only between your Java application than you can pass the actual reference to the object. Here is an example of my attempt to do something like this by dragging a Swing component between panels:

import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.event.*;
import java.beans.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.plaf.*;
import javax.swing.text.*;
import java.io.*;

public class DragComponent extends JPanel
{
//  public final static DataFlavor COMPONENT_FLAVOR = new DataFlavor(Component[].class, "Component Array");
    public static DataFlavor COMPONENT_FLAVOR;

    public DragComponent()
    {
        try
        {
            COMPONENT_FLAVOR = new DataFlavor(DataFlavor.javaJVMLocalObjectMimeType + ";class="" + Component[].class.getName() + """);
        }
        catch(Exception e)
        {
            System.out.println(e);
        }

        setLayout(null);
        setTransferHandler( new PanelHandler() );

        MouseListener listener = new MouseAdapter()
        {
            @Override
            public void mousePressed(MouseEvent e)
            {
                JComponent c = (JComponent) e.getSource();
                TransferHandler handler = c.getTransferHandler();
                handler.exportAsDrag(c, e, TransferHandler.MOVE);
            }
        };

        TransferHandler handler = new ComponentHandler();

        for (int i = 0; i < 5; i++)
        {
            JLabel label = new JLabel("Label " + i);
            label.setSize( label.getPreferredSize() );
            label.setLocation(30 * (i+1), 30 * (i+1));
            label.addMouseListener( listener );
            label.setTransferHandler( handler );
            add( label );
        }
    }

    private static void createAndShowUI()
    {
        DragComponent north = new DragComponent();
        north.setBackground(Color.RED);
        north.setPreferredSize( new Dimension(200, 200) );

        DragComponent south = new DragComponent();
        south.setBackground(Color.YELLOW);
        south.setPreferredSize( new Dimension(200, 200) );

        JFrame frame = new JFrame("DragComponent");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(north, BorderLayout.NORTH);
        frame.add(south, BorderLayout.SOUTH);
        frame.pack();
        frame.setLocationByPlatform( true );
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowUI();
            }
        });
    }
}

class ComponentHandler extends TransferHandler
{
    @Override
    public int getSourceActions(JComponent c)
    {
        return MOVE;
    }

    @Override
    public Transferable createTransferable(final JComponent c)
    {
        return new Transferable()
        {
            @Override
            public Object getTransferData(DataFlavor flavor)
            {
                Component[] components = new Component[1];
                components[0] = c;
                return components;
            }

            @Override
            public DataFlavor[] getTransferDataFlavors()
            {
                DataFlavor[] flavors = new DataFlavor[1];
                flavors[0] = DragComponent.COMPONENT_FLAVOR;
                return flavors;
            }

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

    @Override
    public void exportDone(JComponent c, Transferable t, int action)
    {
        System.out.println(c.getBounds());
    }
}

class PanelHandler extends TransferHandler
{
    @Override
    public boolean canImport(TransferSupport support)
    {
        if (!support.isDrop())
        {
            return false;
        }

        boolean canImport = support.isDataFlavorSupported(DragComponent.COMPONENT_FLAVOR);
        return canImport;
    }

    @Override
    public boolean importData(TransferSupport support)
    {
        if (!canImport(support))
        {
            return false;
        }

        Component[] components;

        try
        {
            components = (Component[])support.getTransferable().getTransferData(DragComponent.COMPONENT_FLAVOR);
        }
        catch (Exception e)
        {
            e.printStackTrace();
            return false;
        }

        Component component = components[0];
        Container container = (Container)support.getComponent();
        container.add(component);
//      container.revalidate();
//      container.repaint();
        container.getParent().revalidate();
        container.getParent().repaint();

        JLabel label = (JLabel)component;
        DropLocation location = support.getDropLocation();
        System.out.println(label.getText() + " + " + location.getDropPoint());
        label.setLocation( location.getDropPoint() );
        return true;
    }
}

这篇关于可以避免在同一应用程序中的 JComponent 之间的 DnD 中进行序列化吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！