Question

我相信通过为元素创建JMenu等可以在JComboBoxes下创建子菜单，这实际上基本上意味着创建自己的自定义组件。我还看了几个例子，它很复杂，似乎有一些问题或其他问题。

所以基本上我的问题是可以以某种方式以某种方式创建看起来像JComboBox但也支持子菜单的东西。

Answer 1

这是一个例子： http://www.java2s.com/Code/Java/Swing-Components/ComboBoxMenuExample.htm

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.Icon;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
import javax.swing.UIManager;
import javax.swing.border.EtchedBorder;
import javax.swing.border.TitledBorder;
import javax.swing.plaf.basic.BasicArrowButton;

public class ComboBoxMenuExample extends JFrame {

  public ComboBoxMenuExample() {
  super("ComboBoxMenu Example");

String[] itemStr = { "name", "Red", "Blue", "number", "255,0,0",
    "0,0,255",
    // separator
    "system", "control", "controlHighlight", "controlShadow",
    "text"};

JMenuItem[] menuItems = new JMenuItem[7];
menuItems[0] = new JMenuItem(itemStr[1]);
menuItems[1] = new JMenuItem(itemStr[2]);
menuItems[2] = new JMenuItem(itemStr[4]);
menuItems[3] = new JMenuItem(itemStr[5]);
menuItems[4] = new JMenuItem(itemStr[8]);
menuItems[5] = new JMenuItem(itemStr[9]);
menuItems[6] = new JMenuItem(itemStr[10]);

JMenu[] menus = new JMenu[4];
menus[0] = new JMenu(itemStr[0]);
menus[1] = new JMenu(itemStr[3]);
menus[2] = new JMenu(itemStr[6]);
menus[3] = new JMenu(itemStr[7]);

menus[0].add(menuItems[0]);
menus[0].add(menuItems[1]);
menus[1].add(menuItems[2]);
menus[1].add(menuItems[3]);
menus[3].add(menuItems[4]);
menus[3].add(menuItems[5]);
menus[2].add(menus[3]);
menus[2].add(menuItems[6]);

JMenu menu = ComboMenuBar.createMenu(menuItems[0].getText());
menu.add(menus[0]);
menu.add(menus[1]);
menu.addSeparator();
menu.add(menus[2]);

ComboMenuBar comboMenu = new ComboMenuBar(menu);

JComboBox combo = new JComboBox();
combo.addItem(itemStr[1]);
combo.addItem(itemStr[2]);
combo.addItem(itemStr[4]);
combo.addItem(itemStr[5]);
combo.addItem(itemStr[8]);
combo.addItem(itemStr[9]);
combo.addItem(itemStr[10]);

getContentPane().setLayout(new FlowLayout());
getContentPane().add(new ComboPanel("Fake ComboBox", comboMenu));
getContentPane().add(new ComboPanel("ComboBox", combo));
}

class ComboPanel extends JPanel {
ComboPanel(String title, JComponent c) {
  setLayout(new FlowLayout());
  setBorder(new TitledBorder(title));
  add(c);
}
}

public static void main(String args[]) {
try {
    UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
} catch (Exception evt) {}

ComboBoxMenuExample frame = new ComboBoxMenuExample();
frame.addWindowListener(new WindowAdapter() {
  public void windowClosing(WindowEvent e) {
    System.exit(0);
  }
});
frame.setSize(370, 100);
frame.setVisible(true);
}
}

class ComboMenuBar extends JMenuBar {

JMenu menu;

Dimension preferredSize;

public ComboMenuBar(JMenu menu) {
this.menu = menu;

Color color = UIManager.getColor("Menu.selectionBackground");
UIManager.put("Menu.selectionBackground", UIManager
    .getColor("Menu.background"));
menu.updateUI();
UIManager.put("Menu.selectionBackground", color);

MenuItemListener listener = new MenuItemListener();
setListener(menu, listener);

add(menu);
}

class MenuItemListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
  JMenuItem item = (JMenuItem) e.getSource();
  menu.setText(item.getText());
  menu.requestFocus();
}
}

private void setListener(JMenuItem item, ActionListener listener) {
if (item instanceof JMenu) {
  JMenu menu = (JMenu) item;
  int n = menu.getItemCount();
  for (int i = 0; i < n; i++) {
    setListener(menu.getItem(i), listener);
  }
} else if (item != null) { // null means separator
  item.addActionListener(listener);
}
}

public String getSelectedItem() {
return menu.getText();
}

public void setPreferredSize(Dimension size) {
preferredSize = size;
}

public Dimension getPreferredSize() {
if (preferredSize == null) {
  Dimension sd = super.getPreferredSize();
  Dimension menuD = getItemSize(menu);
  Insets margin = menu.getMargin();
  Dimension retD = new Dimension(menuD.width, margin.top
      + margin.bottom + menuD.height);
  menu.setPreferredSize(retD);
  preferredSize = retD;
}
return preferredSize;
}

private Dimension getItemSize(JMenu menu) {
Dimension d = new Dimension(0, 0);
int n = menu.getItemCount();
for (int i = 0; i < n; i++) {
  Dimension itemD;
  JMenuItem item = menu.getItem(i);
  if (item instanceof JMenu) {
    itemD = getItemSize((JMenu) item);
  } else if (item != null) {
    itemD = item.getPreferredSize();
  } else {
    itemD = new Dimension(0, 0); // separator
  }
  d.width = Math.max(d.width, itemD.width);
  d.height = Math.max(d.height, itemD.height);
}
return d;
}

public static class ComboMenu extends JMenu {
ArrowIcon iconRenderer;

public ComboMenu(String label) {
  super(label);
  iconRenderer = new ArrowIcon(SwingConstants.SOUTH, true);
  setBorder(new EtchedBorder());
  setIcon(new BlankIcon(null, 11));
  setHorizontalTextPosition(JButton.LEFT);
  setFocusPainted(true);
}

public void paintComponent(Graphics g) {
  super.paintComponent(g);
  Dimension d = this.getPreferredSize();
  int x = Math.max(0, d.width - iconRenderer.getIconWidth() - 3);
  int y = Math.max(0,
      (d.height - iconRenderer.getIconHeight()) / 2 - 2);
  iconRenderer.paintIcon(this, g, x, y);
}
}

public static JMenu createMenu(String label) {
return new ComboMenu(label);
}

}

class ArrowIcon implements Icon, SwingConstants {
 private static final int DEFAULT_SIZE = 11;

//private static final int DEFAULT_SIZE = 5;

private int size;

private int iconSize;

private int direction;

private boolean isEnabled;

private BasicArrowButton iconRenderer;

public ArrowIcon(int direction, boolean isPressedView) {
this(DEFAULT_SIZE, direction, isPressedView);
}

public ArrowIcon(int iconSize, int direction, boolean isEnabled) {
this.size = iconSize / 2;
this.iconSize = iconSize;
this.direction = direction;
this.isEnabled = isEnabled;
iconRenderer = new BasicArrowButton(direction);
}

public void paintIcon(Component c, Graphics g, int x, int y) {
iconRenderer.paintTriangle(g, x, y, size, direction, isEnabled);
}

public int getIconWidth() {
//int retCode;
switch (direction) {
case NORTH:
case SOUTH:
  return iconSize;
case EAST:
case WEST:
  return size;
}
return iconSize;
}

public int getIconHeight() {
switch (direction) {
case NORTH:
case SOUTH:
  return size;
case EAST:
case WEST:
  return iconSize;
}
return size;
}
}

class BlankIcon implements Icon {
private Color fillColor;

private int size;

public BlankIcon() {
this(null, 11);
}

public BlankIcon(Color color, int size) {
//UIManager.getColor("control")
//UIManager.getColor("controlShadow")
fillColor = color;

this.size = size;
}

public void paintIcon(Component c, Graphics g, int x, int y) {
if (fillColor != null) {
  g.setColor(fillColor);
  g.drawRect(x, y, size - 1, size - 1);
}
}

public int getIconWidth() {
return size;
}

public int getIconHeight() {
return size;
} 
}

我在这里测试过并且运行得很好看起来有点复杂，但如果你仔细看看代码会理解

JComboBox子菜单项

1 个答案: