在Java中从JButton拖放到JComponent

Question

我在互联网上搜索了如何将JButtons拖放到对象的示例，但我无法使其工作。

我的程序所做的是，当我单击一个按钮时，对象更新了一个字段（使用selectedobject.setField（））。我希望能够通过拖动JButton而不是单击来做到这一点。

我该怎么做？我找到了这个，并试图输入我的代码：

btn.setTransferHandler(new ImageHandler());
btn.addMouseListener(new MouseAdapter() {
    public void mousePressed(MouseEvent e) {
        JComponent c = (JComponent)e.getSource();
        TransferHandler handler = c.getTransferHandler();
        handler.exportAsDrag(c, e, TransferHandler.COPY);
    }
});

我从这里参加了ImageHandler课程。

Answer 1

拖放是一袋松脆的胡萝卜...没有得到“核心”API和更新的“传输”API这一事实的帮助，所以很容易混淆

下面的示例使用“传输”API，基本上将字符串值从按钮传输到 JLabel。

import java.awt.Color;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.Transferable;
import java.awt.dnd.DnDConstants;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.TransferHandler;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.CompoundBorder;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;

public class Test {

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

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridLayout(1, 2));
            add(createLeftPanel());
            add(createRightPanel());

        }

        protected JPanel createLeftPanel() {
            JPanel panel = new JPanel(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.fill = GridBagConstraints.HORIZONTAL;
            gbc.weightx = 1;
            for (int index = 0; index < 10; index++) {
                JButton btn = new JButton(Integer.toString(index + 1));
                panel.add(btn, gbc);
                btn.setTransferHandler(new ValueExportTransferHandler(Integer.toString(index + 1)));

                btn.addMouseMotionListener(new MouseAdapter() {
                    @Override
                    public void mouseDragged(MouseEvent e) {
                        JButton button = (JButton) e.getSource();
                        TransferHandler handle = button.getTransferHandler();
                        handle.exportAsDrag(button, e, TransferHandler.COPY);
                    }
                });
            }
            return panel;
        }

        protected JPanel createRightPanel() {
            JPanel panel = new JPanel(new GridBagLayout());
            JLabel label = new JLabel("Drop in");
            label.setBorder(new CompoundBorder(new LineBorder(Color.DARK_GRAY), new EmptyBorder(20, 20, 20, 20)));
            label.setTransferHandler(new ValueImportTransferHandler());
            panel.add(label);
            return panel;
        }

    }

    public static class ValueExportTransferHandler extends TransferHandler {

        public static final DataFlavor SUPPORTED_DATE_FLAVOR = DataFlavor.stringFlavor;
        private String value;

        public ValueExportTransferHandler(String value) {
            this.value = value;
        }

        public String getValue() {
            return value;
        }

        @Override
        public int getSourceActions(JComponent c) {
            return DnDConstants.ACTION_COPY_OR_MOVE;
        }

        @Override
        protected Transferable createTransferable(JComponent c) {
            Transferable t = new StringSelection(getValue());
            return t;
        }

        @Override
        protected void exportDone(JComponent source, Transferable data, int action) {
            super.exportDone(source, data, action);
            // Decide what to do after the drop has been accepted
        }

    }

    public static class ValueImportTransferHandler extends TransferHandler {

        public static final DataFlavor SUPPORTED_DATE_FLAVOR = DataFlavor.stringFlavor;

        public ValueImportTransferHandler() {
        }

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

        @Override
        public boolean importData(TransferHandler.TransferSupport support) {
            boolean accept = false;
            if (canImport(support)) {
                try {
                    Transferable t = support.getTransferable();
                    Object value = t.getTransferData(SUPPORTED_DATE_FLAVOR);
                    if (value instanceof String) {
                        Component component = support.getComponent();
                        if (component instanceof JLabel) {
                            ((JLabel) component).setText(value.toString());
                            accept = true;
                        }
                    }
                } catch (Exception exp) {
                    exp.printStackTrace();
                }
            }
            return accept;
        }
    }
}

我已经尽力将TransferHandler分开，允许“拖放”和“拖放”版本。您不必“必须”这样做，并且您“可以”使用单个TransferHandler来执行这两个操作，这取决于您。

您必须修改＜code＞ValueExportTransferHandler

您还可以查看将自定义对象从JList拖放到JLabel中的另一个示例。。。