java - 使用 transferHandler 将文本从 JLabel 拖放到 JTable

Question

我正在按照下面提到的教程进行操作。在主题下Extending Default DnD Support本教程的第一个应用程序有一个 JTextArea、一个 JList 和一个 JTable。

而且效果很好。此外，我还使用了一个 JLabel。我将此标签的传输处理程序设置为:

jLabel1.setTransferHandler(new TransferHandler("text"));

当我把这个标签拖到 table 上时，它不接受。但它适用于文本区域中的字符串。

如何将文本从标签拖放到表格中？

Answer 1

new TransferHandler("text");

https://docs.oracle.com/javase/8/docs/api/javax/swing/TransferHandler.html

This class is implemented to provide a default behavior of transferring a component property simply by specifying the name of the property in the constructor. For example, to transfer the foreground color from one component to another either via the clipboard or a drag and drop operation a TransferHandler can be constructed with the string "foreground". The built in support will use the color returned by getForeground as the source of the transfer, and setForeground for the target of a transfer.

JTable 没有setText(String) 方法。因此，您需要覆盖 TransferHander#importData(...) 方法以将数据导入到 JTable 的单元格中。

import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.table.*;

public class DnDTest {
  public JComponent makeUI() {
    JTable table = new JTable(5, 3);
    table.setAutoCreateRowSorter(true);
    table.setTransferHandler(new ToTransferHandler());

    JLabel label = new JLabel("aaaaaaaaaaaa");
    label.setTransferHandler(new TransferHandler("text"));
    label.addMouseListener(new MouseAdapter() {
      @Override public void mousePressed(MouseEvent e) {
        JComponent c = (JComponent) e.getSource();
        c.getTransferHandler().exportAsDrag(c, e, TransferHandler.COPY);
      }
    });

    JPanel p = new JPanel(new BorderLayout());
    p.add(new JScrollPane(table));
    p.add(label, BorderLayout.SOUTH);
    return p;
  }
  public static void main(String... args) {
    EventQueue.invokeLater(() -> {
      JFrame f = new JFrame();
      f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      f.getContentPane().add(new DnDTest().makeUI());
      f.setSize(320, 240);
      f.setLocationRelativeTo(null);
      f.setVisible(true);
    });
  }
}

//@see https://docs.oracle.com/javase/tutorial/uiswing/dnd/dropactiondemo.html
class ToTransferHandler extends TransferHandler {
  @Override public boolean canImport(TransferHandler.TransferSupport support) {
    return getPropertyDataFlavor(String.class, support.getDataFlavors()) != null;
  }
  @Override public boolean importData(TransferHandler.TransferSupport support) {
    // if we can't handle the import, say so
    if (!canImport(support)) {
      return false;
    }

    DataFlavor flavor = getPropertyDataFlavor(String.class, support.getDataFlavors());

    // fetch the data and bail if this fails
    String data;
    try {
      data = (String) support.getTransferable().getTransferData(flavor);
    } catch (UnsupportedFlavorException | java.io.IOException e) {
      return false;
    }

    JTable.DropLocation dl = (JTable.DropLocation) support.getDropLocation();
    JTable table = (JTable) support.getComponent();
    table.setValueAt(data, dl.getRow(), dl.getColumn());
    return true;
  }
  //@see TransferHandler.java private DataFlavor getPropertyDataFlavor(...) {
  private DataFlavor getPropertyDataFlavor(Class<?> k, DataFlavor[] flavors) {
    for (int i = 0; i < flavors.length; i++) {
      DataFlavor flavor = flavors[i];
      if ("application".equals(flavor.getPrimaryType()) &&
          "x-java-jvm-local-objectref".equals(flavor.getSubType()) &&
          k.isAssignableFrom(flavor.getRepresentationClass())) {
        return flavor;
      }
    }
    return null;
  }
}