java 使用拖放重新排序 JList

Reordering JList with Drag and Drop

提问by UserOrNotAnUser

I encountered a problem regarding reordering elements in a JList using Drag and Drop. This following code is a modification of a code where you could drag elements from one JList to another (worked only one way). I tried to make it usable for only one JList, but the elements can't even be dragged out of the list. So I guess it can't be done this way. Any ideas what I'm doing wrong or not taking into consideration?

我遇到了关于使用拖放对 JList 中的元素重新排序的问题。以下代码是对代码的修改，您可以在其中将元素从一个 JList 拖动到另一个（仅以一种方式工作）。我试图让它只对一个 JList 可用，但元素甚至不能被拖出列表。所以我想它不能以这种方式完成。任何想法我做错了什么或没有考虑到什么？

The idea is to get it to work for a Jlist with thumbnails, but since I can't even get it to work with just strings... I have been looking into several D'n'D tutorials, but still I can't get it to work. Any help is appreciated.

这个想法是让它为带有缩略图的 Jlist 工作，但因为我什至不能让它只使用字符串......我一直在研究几个 D'n'D 教程，但我仍然不能让它工作。任何帮助表示赞赏。

import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.datatransfer.*;
import java.io.IOException;

public class DragAndDrop extends JFrame {


DefaultListModel<String> transport = new DefaultListModel<String>();
JList<String> transportList = new JList<String>(transport);

public DragAndDrop() {
    setLayout(new FlowLayout());

    transport.addElement("Bike");
    transport.addElement("Car");
    transport.addElement("Truck");
    transport.addElement("Boat");

    JScrollPane transportScroll = new JScrollPane(transportList);
    transportScroll.setBorder(new TitledBorder("Transportation"));

    add(transportScroll);

    transportList.setDragEnabled(true);

    transportList.setTransferHandler(new TransferHandler() {
        int index;  

        @Override
        public int getSourceActions(JComponent comp) {
            return COPY_OR_MOVE;
        }

        @Override
        public Transferable createTransferable(JComponent comp) {
            index = transportList.getSelectedIndex(); 
            return new StringSelection(transportList.getSelectedValue());
        }


        @Override
        public void exportDone( JComponent comp, Transferable trans, int action ) {
            if (action==MOVE) {
                transport.remove(index);
            }
        }
    });

    transportList.setDropMode(DropMode.ON);

    transportList.setTransferHandler(new TransferHandler() {
        @Override
        public boolean canImport(TransferHandler.TransferSupport support) {
            // data of type string?
            return support.isDataFlavorSupported(DataFlavor.stringFlavor);
        }

        @Override
        public boolean importData(TransferHandler.TransferSupport support) {
            try {
                // convert data to string
                String s = (String)support.getTransferable().getTransferData(DataFlavor.stringFlavor);
                JList.DropLocation dl = (JList.DropLocation)support.getDropLocation();
                transport.add(dl.getIndex(),s);
                return true;
            } 
            catch (UnsupportedFlavorException e) {} 
            catch (IOException e) {}

            return false;
        }
    });

    pack();

    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
}

public static void main(String[] args) {
    new DragAndDrop();
}

}

PS. Sorry if this turns out to be a re-post.

附注。对不起，如果这是一个重新发布。

EDITI think I got it fixed: had to different transferHandlers - should only have one with all the methods from the second one as well.

编辑我想我已经解决了：必须使用不同的 transferHandlers - 应该只有一个包含第二个方法的所有方法。

回答by aterai

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DragSource;
import java.io.IOException;
import java.io.Serializable;
import java.util.Arrays;
import java.util.Objects;
// import javax.activation.ActivationDataFlavor;
// import javax.activation.DataHandler;
import javax.swing.BorderFactory;
import javax.swing.DefaultListModel;
import javax.swing.DropMode;
import javax.swing.Icon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.ListCellRenderer;
import javax.swing.ListSelectionModel;
import javax.swing.TransferHandler;
import javax.swing.UIManager;
import javax.swing.WindowConstants;

public class DragAndDropTest {
  public JComponent makeUI() {
    DefaultListModel<Thumbnail> m = new DefaultListModel<>();
    for (String s : Arrays.asList("error", "information", "question", "warning")) {
      m.addElement(new Thumbnail(s));
    }

    JList<Thumbnail> list = new JList<>(m);
    list.getSelectionModel().setSelectionMode(
      ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
    list.setTransferHandler(new ListItemTransferHandler());
    list.setDropMode(DropMode.INSERT);
    list.setDragEnabled(true);
    // https://java-swing-tips.blogspot.com/2008/10/rubber-band-selection-drag-and-drop.html
    list.setLayoutOrientation(JList.HORIZONTAL_WRAP);
    list.setVisibleRowCount(0);
    list.setFixedCellWidth(80);
    list.setFixedCellHeight(80);
    list.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

    list.setCellRenderer(new ListCellRenderer<Thumbnail>() {
      private final JPanel p = new JPanel(new BorderLayout());
      private final JLabel icon = new JLabel((Icon)null, JLabel.CENTER);
      private final JLabel label = new JLabel("", JLabel.CENTER);

      @Override
      public Component getListCellRendererComponent(
        JList<? extends Thumbnail> list, Thumbnail value, int index,
        boolean isSelected, boolean cellHasFocus) {
        icon.setIcon(value.icon);
        label.setText(value.name);
        label.setForeground(isSelected ? list.getSelectionForeground()
                            : list.getForeground());
        p.add(icon);
        p.add(label, BorderLayout.SOUTH);
        p.setBackground(isSelected ? list.getSelectionBackground()
                        : list.getBackground());
        return p;
      }
    });
    return new JScrollPane(list);
  }

  public static void main(String[] args) {
    EventQueue.invokeLater(() -> createAndShowGUI());
  }

  public static void createAndShowGUI() {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    f.getContentPane().add(new DragAndDropTest().makeUI());
    f.setSize(320, 240);
    f.setLocationRelativeTo(null);
    f.setVisible(true);
  }
}

class Thumbnail implements Serializable {
  public final String name;
  public final Icon icon;
  public Thumbnail(String name) {
    this.name = name;
    this.icon = UIManager.getIcon("OptionPane." + name + "Icon");
  }
}

// @camickr already suggested above.
// https://docs.oracle.com/javase/tutorial/uiswing/dnd/dropmodedemo.html
@SuppressWarnings("serial")
class ListItemTransferHandler extends TransferHandler {
  protected final DataFlavor localObjectFlavor;
  protected int[] indices;
  protected int addIndex = -1; // Location where items were added
  protected int addCount; // Number of items added.

  public ListItemTransferHandler() {
    super();
    // localObjectFlavor = new ActivationDataFlavor(
    //   Object[].class, DataFlavor.javaJVMLocalObjectMimeType, "Array of items");
    localObjectFlavor = new DataFlavor(Object[].class, "Array of items");
  }

  @Override
  protected Transferable createTransferable(JComponent c) {
    JList<?> source = (JList<?>) c;
    c.getRootPane().getGlassPane().setVisible(true);

    indices = source.getSelectedIndices();
    Object[] transferedObjects = source.getSelectedValuesList().toArray(new Object[0]);
    // return new DataHandler(transferedObjects, localObjectFlavor.getMimeType());
    return new Transferable() {
      @Override public DataFlavor[] getTransferDataFlavors() {
        return new DataFlavor[] {localObjectFlavor};
      }
      @Override public boolean isDataFlavorSupported(DataFlavor flavor) {
        return Objects.equals(localObjectFlavor, flavor);
      }
      @Override public Object getTransferData(DataFlavor flavor)
            throws UnsupportedFlavorException, IOException {
        if (isDataFlavorSupported(flavor)) {
          return transferedObjects;
        } else {
          throw new UnsupportedFlavorException(flavor);
        }
      }
    };
  }

  @Override
  public boolean canImport(TransferSupport info) {
    return info.isDrop() && info.isDataFlavorSupported(localObjectFlavor);
  }

  @Override
  public int getSourceActions(JComponent c) {
    Component glassPane = c.getRootPane().getGlassPane();
    glassPane.setCursor(DragSource.DefaultMoveDrop);
    return MOVE; // COPY_OR_MOVE;
  }

  @SuppressWarnings("unchecked")
  @Override
  public boolean importData(TransferSupport info) {
    TransferHandler.DropLocation tdl = info.getDropLocation();
    if (!canImport(info) || !(tdl instanceof JList.DropLocation)) {
      return false;
    }

    JList.DropLocation dl = (JList.DropLocation) tdl;
    JList target = (JList) info.getComponent();
    DefaultListModel listModel = (DefaultListModel) target.getModel();
    int max = listModel.getSize();
    int index = dl.getIndex();
    index = index < 0 ? max : index; // If it is out of range, it is appended to the end
    index = Math.min(index, max);

    addIndex = index;

    try {
      Object[] values = (Object[]) info.getTransferable().getTransferData(localObjectFlavor);
      for (int i = 0; i < values.length; i++) {
        int idx = index++;
        listModel.add(idx, values[i]);
        target.addSelectionInterval(idx, idx);
      }
      addCount = values.length;
      return true;
    } catch (UnsupportedFlavorException | IOException ex) {
      ex.printStackTrace();
    }

    return false;
  }

  @Override
  protected void exportDone(JComponent c, Transferable data, int action) {
    c.getRootPane().getGlassPane().setVisible(false);
    cleanup(c, action == MOVE);
  }

  private void cleanup(JComponent c, boolean remove) {
    if (remove && Objects.nonNull(indices)) {
      if (addCount > 0) {
        // https://github.com/aterai/java-swing-tips/blob/master/DragSelectDropReordering/src/java/example/MainPanel.java
        for (int i = 0; i < indices.length; i++) {
          if (indices[i] >= addIndex) {
            indices[i] += addCount;
          }
        }
      }
      JList source = (JList) c;
      DefaultListModel model = (DefaultListModel) source.getModel();
      for (int i = indices.length - 1; i >= 0; i--) {
        model.remove(indices[i]);
      }
    }

    indices = null;
    addCount = 0;
    addIndex = -1;
  }
}

回答by camickr

See the Drop Demofrom the Swing tutorial on DnD for an example that will drop on the same JList or another JList.

请参阅DnD 上的 Swing 教程中的Drop Demo，了解将在同一 JList 或另一个 JList 上拖放的示例。

回答by Dan

As the OP noted in their edit to the original question, the problem in the example given was that there were two transfer handlers and as camickrrightly pointed out in their answer, there is an example in the Java Tutorials which will work.

正如 OP 在对原始问题的编辑中指出的那样，给出的示例中的问题是有两个传输处理程序，并且正如camickr在他们的回答中正确指出的那样，Java 教程中有一个可以工作的示例。

The problem with the example in the Java Tutorials is that, when using DropMode.INSERTand moving an item in the current JListto before the selected index, the item is duplicated. This deletes an item in the JList, puts a duplicate of the item in the place you wanted it to go, and leaves the original selected item as it is.

Java 教程中示例的问题在于，当使用DropMode.INSERT当前项目并将其移动JList到所选索引之前，该项目被复制。这将删除 中的一个项目，将该项目JList的副本放置在您想要它去的地方，并保持原来的选定项目不变。

So, for those interested, here is an example which fixes that problem based upon the JList<String>example provided in the OP's question.

因此，对于那些感兴趣的人，这里有一个示例，它根据JList<String>OP 问题中提供的示例解决了该问题。

import java.awt.EventQueue;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;

import javax.swing.DefaultListModel;
import javax.swing.DropMode;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.ListSelectionModel;
import javax.swing.TransferHandler;

@SuppressWarnings("serial")
public class GUI extends JFrame {
    protected GUI() {
        super("Simple Rearrangeable List");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        createPanel();
        setBounds(10, 10, 350, 500);
        setVisible(true);
    }

    private void createPanel() {
        DefaultListModel<String> strings = new DefaultListModel<String>();

        for(int i = 1; i <= 100; i++) {
            strings.addElement("Item " + i);
        }

        JList<String> dndList = new JList<String>(strings);
        dndList.setDragEnabled(true);
        dndList.setDropMode(DropMode.INSERT);
        dndList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        dndList.setTransferHandler(new TransferHandler() {
            private int index;
            private boolean beforeIndex = false; //Start with `false` therefore if it is removed from or added to the list it still works

            @Override
            public int getSourceActions(JComponent comp) {
                return MOVE;
            }

            @Override
            public Transferable createTransferable(JComponent comp) {
                index = dndList.getSelectedIndex(); 
                return new StringSelection(dndList.getSelectedValue());
            }

            @Override
            public void exportDone(JComponent comp, Transferable trans, int action) {
                if (action == MOVE) {
                    if(beforeIndex)
                        strings.remove(index + 1);
                    else
                        strings.remove(index);
                }
            }

            @Override
            public boolean canImport(TransferHandler.TransferSupport support) {
                return support.isDataFlavorSupported(DataFlavor.stringFlavor);
            }

            @Override
            public boolean importData(TransferHandler.TransferSupport support) {
                try {
                    String s = (String) support.getTransferable().getTransferData(DataFlavor.stringFlavor);
                    JList.DropLocation dl = (JList.DropLocation) support.getDropLocation();
                    strings.add(dl.getIndex(), s);
                    beforeIndex = dl.getIndex() < index ? true : false;
                    return true;
                } catch (UnsupportedFlavorException | IOException e) {
                    e.printStackTrace();
                }

                return false;
            }
        });

        JScrollPane scrollPane = new JScrollPane(dndList);
        getContentPane().add(scrollPane);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new GUI());
    }
}