java 将 JMenu 添加到 JPanel

Adding a JMenu to a JPanel

提问by paranoia25

I need to have a JMenu(the one with the arrow on right which can display JMenuItem) in a JPanel. The problem is that when I do that the JMenuis not activate on mouse rollover... I don't know how to do that and if it's possible.

我需要有一个JMenu（具有在其上可以显示右侧的箭头JMenuItema）中JPanel。问题是，当我这样做时，JMenu鼠标悬停时不会激活......我不知道如何做到这一点，如果可能的话。

回答by Guillaume Polet

If you wrap your JMenuin a JMenuBar, it works as expected.

如果你将你的包裹JMenu在 a 中JMenuBar，它会按预期工作。

Here is a demo example:

这是一个演示示例：

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;

public class TestMenus {

    private JMenuBar createMenuBar(String name, int depth) {
        JMenuBar bar = new JMenuBar();
        bar.add(createMenu(name, depth));
        return bar;
    }

    private JMenu createMenu(String name, int depth) {
        JMenu menu = new JMenu(name);
        for (int i = 0; i < 5; i++) {
            if (depth > 0) {
                menu.add(createMenu("sub-" + name, depth - 1));
            }
        }
        for (int i = 0; i < 5; i++) {
            menu.add(createMenuItem("Menu item " + (i + 1)));
        }
        return menu;
    }

    private JMenuItem createMenuItem(String name) {
        final JMenuItem jMenuItem = new JMenuItem(name);
        jMenuItem.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(jMenuItem, "Successfully pressed a menu item");
            }
        });
        return jMenuItem;
    }

    protected void initUI() {
        JFrame frame = new JFrame(TestMenus.class.getSimpleName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(createMenuBar("Root menu", 3));
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestMenus().initUI();
            }
        });
    }

}

An the result:

结果：

回答by Michael Peterson

Here is another way to solve this which I think is closer to what you want. It involves extending JMenuBarto give it the look of a JMenuObject.

这是解决这个问题的另一种方法，我认为它更接近你想要的。它涉及扩展JMenuBar以赋予它JMenu对象的外观。

The class contains a JMenuObject called menu. The add methods are overridden so you are adding to menu instead of the JMenuBar(You may have to override a few more add methods to make this perfect).

该类包含一个JMenu名为 menu的对象。add 方法被覆盖，因此您将添加到菜单而不是JMenuBar（您可能需要覆盖更多的 add 方法以使其完美）。

There are a few options with painting. I wasn't sure if you wanted the button style look of the JMenuBar, so I included a few comments on some options to customize that, as well as the underline look of the JMenuBar.

绘画有几种选择。我不知道，如果你想要的按钮样式的样子JMenuBar，所以我包括一些选项的一些意见，以自定义，以及的下划线的样子JMenuBar。

Here is the result of the button look with no border:

这是没有边框的按钮外观的结果：

Here is the result with no button look and no border:

这是没有按钮外观和边框的结果：

import java.awt.*;
import javax.swing.*;

public class JPanelMenu extends JMenuBar{

public static void main(String[] args) {
    JFrame f = new JFrame("Menu Test");
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JMenu jmenu = new JMenu("J Menu");
    jmenu.add(new JMenuItem("Menu Item"));

    JPanelMenu m = new JPanelMenu("Menu");
    m.add(jmenu);
    m.add(new JMenuItem("Menu Item 1"));
    m.add(new JMenuItem("Menu Item 2"));

    JPanel background = new JPanel();
    background.add(m);      
    f.setContentPane(background);
    f.pack();
    f.setVisible(true);
}

//This is the JMenu that is shown
private JMenu menu;

public JPanelMenu(String title) {
    super();
    menu = new JMenu(title);
    super.add(menu);
}

@Override
public Component add(Component comp) {
    //You add the the JMenu instead of the JMenuBar
    return menu.add(comp);
}

@Override
public JMenu add(JMenu c) {
    //You add the the JMenu instead of the JMenuBar
    return (JMenu) menu.add(c);
}

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);

    //Include these two lines to remove the button look
    //Or remove this method to keep the button look
    //g.setColor(getBackground());
    //g.fillRect(0, 0, getWidth(), getHeight());
}

@Override
protected void paintBorder(Graphics g) {
    //Remove this line to remove the underline look
    //when you remove the button look
    //An alternative is to you setBorderPainted(false);
    //when you create the object or in the constructor
    //Or remove this method to keep the border
    //super.paintBorder(g);
}
}

回答by Vuk Vasi?

You must pass a BorderLayoutin JPanel layout then you can add menu bar in panel:

您必须在 JPanel 布局中传递一个BorderLayout然后您可以在面板中添加菜单栏：

JPanel p = new JPanel();
p.setLayout(new BorderLayout());
p.add(menubar, BorderLayout.NORTH);