构建下拉菜单按钮，构建下拉菜单,public class

构建下拉菜单按钮，构建下拉菜单,public class

public class DropDownComponent extends JComponent         implements ActionListener, AncestorListener {        protected JComponent drop_down_comp;        protected JComponent visible_comp;        protected JButton arrow;        protected JWindow popup;        public DropDownComponent(JComponent vcomp, JComponent ddcomp) {        drop_down_comp = ddcomp;        visible_comp = vcomp;        arrow = new JButton(new MetalComboBoxIcon());        Insets insets = arrow.getMargin();        arrow.setMargin( new Insets( insets.top, 1, insets.bottom, 1 ) );        arrow.addActionListener(this);        addAncestorListener(this);        setupLayout();         }    }    protected void setupLayout() {        GridBagLayout gbl = new GridBagLayout();        GridBagConstraints c = new GridBagConstraints();        setLayout(gbl);        c.weightx = 1.0; c.weighty = 1.0;        c.gridx = 0; c.gridy = 0;        c.fill = c.BOTH;        gbl.setConstraints(visible_comp,c);        add(visible_comp);        c.weightx = 0;        c.gridx++;        gbl.setConstraints(arrow,c);        add(arrow);    }    public void actionPerformed(ActionEvent evt) {        // build pop-up window        popup = new JWindow(getFrame(null));        popup.getContentPane().add(drop_down_comp);        popup.addWindowFocusListener(new WindowAdapter() {            public void windowLostFocus(WindowEvent evt) {                 popup.setVisible(false);            }        });        popup.pack();        // show the pop-up window        Point pt = visible_comp.getLocationOnScreen();        pt.translate(0,visible_comp.getHeight());        popup.setLocation(pt);        popup.toFront();        popup.setVisible(true);        popup.requestFocusInWindow();    }    protected Frame getFrame(Component comp) {        if(comp == null) {            comp = this;        }        if(comp.getParent() instanceof Frame) {            return (Frame)comp.getParent();        }        return getFrame(comp.getParent());        }    public void ancestorAdded(AncestorEvent event){        hidePopup();    }    public void ancestorRemoved(AncestorEvent event){        hidePopup();    }    public void ancestorMoved(AncestorEvent event){        if (event.getSource() != popup) {            hidePopup();        }    }    public void hidePopup() {        if(popup != null && popup.isVisible()) {            popup.setVisible(false);        }    }}    public class ColorSelectionPanel extends JPanel {        public ColorSelectionPanel() {            GridBagLayout gbl = new GridBagLayout();            GridBagConstraints c = new GridBagConstraints();            setLayout(gbl);            // reusable listener for each button                    ActionListener color_listener = new ActionListener() {                 public void actionPerformed(ActionEvent evt) {                      selectColor(((JButton)evt.getSource()).getBackground());                 }            };            // set up the standard 12 colors            Color[] colors = new Color[12];            colors[0] = Color.white;            colors[1] = Color.black;            colors[2] = Color.blue;            colors[3] = Color.cyan;            colors[4] = Color.gray;            colors[5] = Color.green;            colors[6] = Color.lightGray;            colors[7] = Color.magenta;            colors[8] = Color.orange;            colors[9] = Color.pink;            colors[10] = Color.red;            colors[11] = Color.yellow;            // lay out the grid            c.gridheight = 1;            c.gridwidth = 1;            c.fill = c.NONE;            c.weightx = 1.0;            c.weighty = 1.0;            for(int i=0; i<3; i++) {                for(int j=0; j<4; j++) {                c.gridx=j;                c.gridy=i;                JButton button = new ColorButton(colors[j+i*4]);                gbl.setConstraints(button,c);                add(button);                button.addActionListener(color_listener);                }            }        }        // fire off a selectedColor property event        protected Color selectedColor = Color.black;        public void selectColor(Color newColor) {            Color oldColor = selectedColor;            selectedColor = newColor;            firePropertyChange("selectedColor",oldColor, newColor);        }    }}    public class ColorButton extends JButton {        public ColorButton(Color col) {            super();            this.setText("");            Dimension dim = new Dimension(15,15);            this.setSize(dim);            this.setPreferredSize(dim);            this.setMinimumSize(dim);            this.setBorderPainted(true);            this.setBackground(col);        }    }    public class DropDownTest extends JPanel {        public static void main(String[] args) {            final JButton status = new JButton("Color");            final JPanel panel = new ColorSelectionPanel();            final DropDownComponent dropdown = new DropDownComponent(status,panel);            panel.addPropertyChangeListener("selectedColor",                new PropertyChangeListener() {                public void propertyChange(PropertyChangeEvent evt) {                dropdown.hidePopup();                                status.setBackground((Color)evt.getNewValue());                }            });            JFrame frame = new JFrame("Drop Down Test");            frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);            frame.getContentPane().setLayout(new BorderLayout(  ));            frame.getContentPane().add("North",dropdown);            frame.getContentPane().add("Center",new JLabel("Drop Down Test"));            frame.pack();            frame.setSize(300,300);            frame.show();        }    }//该片段来自于http://byrx.net