Question

假设我想以这样的方式在Java中创建一个按钮，这样当您单击它时，会出现JPopupMenu。它出现的相关代码是menu.show(button, button.getWidth()/2, button.getHeight()/2);，这使得JPopupMenu的左上角显示在按钮的中心，如下所示：

Current Swing JPopupMenu

但是，我希望它能让左下角位于按钮的中心，就像iTunes一样（左下角有一个按钮，与{的大小相同）它左边的{1}}按钮）：

enter image description here

我尝试通过获取JPopupMenu的高度并将其添加到弹出菜单显示的y坐标来实现这一点，但我发现JPopupMenu在可见之前的高度为0，因为我试图告诉计算机将它显示在何处，所以对我没有帮助。此外，无法在偏移量中进行硬编码，因为弹出窗口中的项目数量不一定相同。

如何才能显示我的高度未知的JPopupMenu，使其左下角的坐标与给定的坐标相匹配？

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。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。

然后我覆盖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合适的偏移量，以便左下角现在出现在组件的中心......

enter image description here

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);
        }

    }
}

使用Mac输出进行更新

enter image description here

按钮示例

您不可能找到满足您需求的解决方案。任何开发人员可以开发的最大技能之一是能够在需要时采取创意并塑造它。

前面的例子涵盖了你需要的所有东西，你只需要能够从概念到解决方案的跨越。

getPopupLocation是组件弹出API的一部分，因此覆盖方法或调用它可能不是你需要的（除非你有一个专用的按钮用于任务，这可能不是一件坏事），所以你需要根据自己的需要调整解决方案......

enter image description here

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);
        }
    }
}

Answer 2

这实际上比我想象的容易得多，并且在大多数情况下都应该有效。我用了你的pastebin代码并玩了一下。在框架上致电setVisible(true)后，我可以致电menu.getPreferredSize()。只需将其打印到标准输出就可以给我java.awt.Dimension[width=31,height=62]。这可以在调用ActionListener之前完成，这样您就可以使用高度。

如果您在菜单中使用边框，则可能需要考虑这一点，但上述情况应该有效。

Answer 3

此答案仅用于备份我对弹出窗口可见性和getPreferredSize（）的评论。

请注意，您可以为弹出窗口获得零首选高度...如果它有零菜单项，那将是合乎逻辑的结论。

再次，MadProgrammer的答案应该被接受。

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JPopupMenu;
import javax.swing.SwingUtilities;

public class ButtonPopup extends JFrame {

    private JButton button;

    public ButtonPopup() {        
        setLayout(new GridBagLayout());

        button = new JButton("Click Meh~ /o/");
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                JPopupMenu popup = new JPopupMenu();
                popup.add(new JMenuItem("A"));
                popup.add(new JMenuItem("B"));
                popup.add(new JMenuItem("C"));

                // you want this
                int height = popup.getPreferredSize().height;
                popup.show(
                        button, button.getWidth() / 2,
                        -height + (button.getHeight() / 2));
            }
        });

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(5, 5, 5, 5);
        add(button, gbc);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();

        setLocationRelativeTo(null);
    }


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

            public void run() {
                new ButtonPopup().setVisible(true);
            }
        });
    }
}

P.S。：我通常不会重复长期死亡的问题，但这次我正在寻找类似的东西，这是在谷歌首次发布。

使用某个左下角坐标进行JPopupMenu显示

3 个答案:

按钮示例