如何在使用FlowLayout的JPanel中垂直居中组件

Question

我有一个特定的面板，其中包含随机数量的项目。此面板添加到使用 BorderLayout 的 JPanel 的 EAST。

我想让它们垂直居中。

我该如何实现？

这是一个代码，您可以运行

public class MainFrame {

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new AlignDemo());
    }
}

class AlignDemo implements Runnable {
    @Override
    public void run(){           
        try {
            JFrame mainWindow = new JFrame();
            mainWindow.getContentPane().add(initPanel());
            mainWindow.pack();
            mainWindow.setVisible(true);
        } catch (Throwable th) {                    
            JOptionPane.showMessageDialog(null,null,"General Error", JOptionPane.ERROR_MESSAGE);                        
        }
    }

    private JPanel initPanel() {
        FlowLayout layout = new FlowLayout(FlowLayout.LEFT);
        layout.setHgap(15);
        JPanel myContent = new JPanel();
        myContent.setPreferredSize(new Dimension(400,200));
        myContent.setBorder(BorderFactory.createLineBorder(Color.blue));
        JButton button1 = new JButton("I'm a button");
        JButton button2 = new JButton("I'm a button");
        JButton button3 = new JButton("I'm a button");
        myContent.add(button1,Component.CENTER_ALIGNMENT);
        myContent.add(button2,Component.CENTER_ALIGNMENT);
        myContent.add(button3,Component.CENTER_ALIGNMENT);
        return myContent;
    }
}

Answer 1

通过组合布局很容易实现。 JPanel 和 FlowLayout (controls) 以相对于彼此定位按钮，作为单个组件放置到 JPanel 和 GridBagLayout (ui).

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

public class CenteredButtons2 {

    private JComponent ui = null;

    CenteredButtons2() {
        initUI();
    }

    public void initUI() {
        if (ui!=null) return;

        ui = new JPanel(new GridBagLayout()); // to center a single component
        ui.setBorder(new EmptyBorder(4,4,4,4));

        JPanel controls = new JPanel(new FlowLayout());
        for (int ii=1; ii<4; ii++) {
            controls.add(new JButton("Button " + ii));
        }
        controls.setBorder(new EmptyBorder(50, 90, 50, 90));
        ui.add(controls);
    }

    public JComponent getUI() {
        return ui;
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception useDefault) {
                }
                CenteredButtons2 o = new CenteredButtons2();

                JFrame f = new JFrame(o.getClass().getSimpleName());
                f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                f.setLocationByPlatform(true);

                f.setContentPane(o.getUI());
                f.pack();
                f.setMinimumSize(f.getSize());

                f.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}

如何在使用FlowLayout的JPanel中垂直居中组件

How to center component vertically in JPanel which useFlowLayout

java

layout

swing

layout-manager