使JPopupMenu以某个左下坐标显示

Question

假设我想以这样的方式在Java中制作一个按钮，这样当你点击它时，就会出现一个JPopupMenu。它出现的相关html" target="_blank">代码是menu.show（button,button.getwidth（）/2,button.getheight()/2）；，它使JPopupMenu的左上角显示在按钮的中心，如下所示：

不过，我希望它的左下角位于按钮的中心，有点像iTunes的做法（左下角下方有一个按钮，大小与左侧的+按钮相同）：

我试图通过获取JPopupMenu的高度并将其添加到弹出菜单正在显示的y坐标来实现这一点，但我发现JPopupMenu在可见之前的高度为0，这对我没有帮助，因为我试图告诉计算机在哪里使其可见。另外，在偏移量中硬编码是不可能的，因为弹出窗口中的项目数量不一定相同。

我如何使它，使我的JPopupMenu与未知的高度可以显示，使它的左下坐标匹配一个给定的坐标？

Answer 1

基本上，这会创建一个弹出菜单，并使用JComponent#SetComponentPopupMenu将其注册到组件中。这意味着我不再需要监视鼠标事件或决定何时显示弹出窗口。

然后重写JComponent#GetPopupLocation并计算我希望弹出窗口出现的位置。

基本上，我得到JComponent#GetComponentPopupMenu，得到它的首选大小，并计算一个适当的偏移量，以便左下角现在出现在组件的中心...

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JPopupMenu;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestPopup02 {

    public static void main(String[] args) {
        new TestPopup02();
    }

    public TestPopup02() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

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

    public class TestPane extends JPanel {

        public TestPane() {
            JPopupMenu menu = new JPopupMenu();
            menu.add(new JMenuItem("Edit Playlist"));
            menu.addSeparator();
            menu.add(new JMenuItem("Check for Available Downloads..."));
            menu.addSeparator();
            menu.add(new JMenuItem("Export..."));
            menu.add(new JMenuItem("Burn Playlist to Disc"));
            menu.add(new JMenuItem("Copy To Play Order"));
            menu.addSeparator();
            menu.add(new JMenuItem("Delete"));
            setComponentPopupMenu(menu);
        }

        @Override
        public Point getPopupLocation(MouseEvent event) {
            // Get the registered popup menu...
            JPopupMenu popup = getComponentPopupMenu();
            // Get the super point, just in case...
            Point pos = super.getPopupLocation(event);
            if (popup != null) {
                // Create a new "point" location
                pos = new Point();
                // get the preferred size of the menu...
                Dimension size = popup.getPreferredSize();
                // Adjust the x position so that the left side of the popup
                // appears at the center of  the component
                pos.x = (getWidth() / 2);
                // Adjust the y position so that the y postion (top corner)
                // is positioned so that the bottom of the popup
                // appears in the center
                pos.y = (getHeight() / 2) - size.height;
            }
            return pos;
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            // Simply draws a cross in the center of the window, so you 
            // know where the center is...
            int width = getWidth() - 1;
            int height = getHeight() - 1;
            g.drawLine(width / 2, 0, width / 2, height);
            g.drawLine(0, height / 2, width, height / 2);
        }

    }
}

你不可能找到一个完全满足你需要的解决方案。任何开发人员所能开发的最伟大的技能之一就是有能力接受一个想法并根据需要塑造它。

前面的例子包含了您所需要的一切，您只需要能够实现从概念到解决方案的飞跃。

GetPopupLocation是组件弹出API的一部分，因此重写方法或调用方法可能都不是您所需要的（除非您有一个用于任务的专用按钮，这可能不是一件坏事），因此您需要使解决方案适应您的需要...

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.GridBagLayout;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JPopupMenu;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestPopup02 {

    public static void main(String[] args) {
        new TestPopup02();
    }

    public TestPopup02() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

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

    public class TestPane extends JPanel {

        private JButton button;
        private JPopupMenu popup;

        public TestPane() {
            popup = new JPopupMenu();
            popup.add(new JMenuItem("Edit Playlist"));
            popup.addSeparator();
            popup.add(new JMenuItem("Check for Available Downloads..."));
            popup.addSeparator();
            popup.add(new JMenuItem("Export..."));
            popup.add(new JMenuItem("Burn Playlist to Disc"));
            popup.add(new JMenuItem("Copy To Play Order"));
            popup.addSeparator();
            popup.add(new JMenuItem("Delete"));

            setLayout(new GridBagLayout());
            button = new JButton("+");
            button.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    popup.pack();
                    Point pos = new Point();
                    // get the preferred size of the menu...
                    Dimension size = popup.getPreferredSize();
                    // Adjust the x position so that the left side of the popup
                    // appears at the center of  the component
                    pos.x = (button.getWidth() / 2);
                    // Adjust the y position so that the y postion (top corner)
                    // is positioned so that the bottom of the popup
                    // appears in the center
                    pos.y = (button.getHeight() / 2) - size.height;
                    popup.show(button, pos.x, pos.y);
                }
            });
            add(button);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            // Simply draws a cross in the center of the window, so you 
            // know where the center is...
            int width = getWidth() - 1;
            int height = getHeight() - 1;
            g.drawLine(width / 2, 0, width / 2, height);
            g.drawLine(0, height / 2, width, height / 2);
        }
    }
}