Java GridBagLayout：使组件左对齐

Question

我有这个布局使用GridBagLayout:

public class Example extends JFrame {
    public Example() {
        Border outline = BorderFactory.createLineBorder(Color.black);
        GridBagLayout gbl = new GridBagLayout();
        GridBagConstraints gbc = new GridBagConstraints();
        JPanel pane = new JPanel(gbl);

        gbc.weighty = 1.0;
        gbc.weightx = 1.0;

        JLabel unitLbl = new JLabel("Unit");
        unitLbl.setBorder(outline);
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.ipadx = 30;
        gbc.ipady = 10;
        gbl.setConstraints(unitLbl, gbc);
        pane.add(unitLbl);

        JLabel typeLbl = new JLabel("Type");
        typeLbl.setBorder(outline);
        gbc.gridx = 0;
        gbc.gridy = 1;
        gbc.ipadx = 30;
        gbc.ipady = 10;
        gbl.setConstraints(typeLbl, gbc);
        pane.add(typeLbl);

        JTextField unitField = new JTextField();
        typeLbl.setBorder(outline);
        gbc.gridx = 1;
        gbc.gridy = 0;
        gbc.ipadx = 30;
        gbc.ipady = 10;
        gbl.setConstraints(unitField, gbc);
        pane.add(unitField);

        String[] type = {"All", "Verb", "Noun", "Adjective"};
        JComboBox<String> comboBox = new JComboBox<String>(type);
        gbc.gridx = 1;
        gbc.gridy = 1;
        gbc.ipadx = 30;
        gbc.ipady = 10;
        gbl.setConstraints(comboBox, gbc);
        pane.add(comboBox);


        add(pane, BorderLayout.CENTER);
        setSize(new Dimension(400, 300));
        getContentPane().setBackground(Color.WHITE);
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Example();
            }
        });
    }
}

在这个例子中，当运行时，似乎每个组件都在框架的中心。但我想要的是：

1. 两个JLabel（unitLbl 和typelbl）将位于框架的左侧
2. JTextField 和 JComboBox 将分别位于两个 JLabel 的右侧，两者之间的距离很小。
3. 此外，我想在网格的位置 (3,0) 添加一个新的JButton，但这个位置的高度是两个JLabel 高度的总和。这意味着，此按钮高度在“两行”上。

如何修复此代码以实现此目标？请帮帮我。

谢谢:)

Answer 1

这样的事情应该可以解决问题：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
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.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class Example extends JFrame {
    public Example() {
        GridBagLayout gbl = new GridBagLayout();
        GridBagConstraints gbc = new GridBagConstraints();
        JPanel pane = new JPanel(gbl);
        gbc.anchor = GridBagConstraints.WEST;

        JLabel unitLbl = new JLabel("Unit");
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.insets = new Insets(3, 3, 3, 30);
        gbl.setConstraints(unitLbl, gbc);
        pane.add(unitLbl);

        JLabel typeLbl = new JLabel("Type");
        gbc.gridx = 0;
        gbc.gridy = 1;
        gbl.setConstraints(typeLbl, gbc);
        pane.add(typeLbl);

        gbc.weightx = 1.0;
        gbc.insets = new Insets(3, 3, 3, 3);

        JTextField unitField = new JTextField();
        gbc.gridx = 1;
        gbc.gridy = 0;
        gbc.fill = GridBagConstraints.BOTH;
        gbl.setConstraints(unitField, gbc);
        pane.add(unitField);

        String[] type = { "All", "Verb", "Noun", "Adjective" };
        JComboBox<String> comboBox = new JComboBox<String>(type);
        gbc.gridx = 1;
        gbc.gridy = 1;
        gbc.fill = GridBagConstraints.NONE;
        gbl.setConstraints(comboBox, gbc);
        pane.add(comboBox);

        final JButton someButton = new JButton("Click me");
        someButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(someButton, "You have clicked " + someButton.getText());
            }
        });

        gbc.gridx = 3;
        gbc.gridy = 0;
        gbc.gridheight = 2;
        gbc.fill = GridBagConstraints.VERTICAL;
        pane.add(someButton, gbc);
        add(pane, BorderLayout.CENTER);
        setSize(new Dimension(400, 300));
        getContentPane().setBackground(Color.WHITE);
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Example();
            }
        });
    }
}

• 需要适当使用weightx/weighty（多余的横向/纵向空间如何重新分配）
• 使用适当的fill 属性（组件是否垂直/水平/同时拉伸？）
• 使用适当的anchor 属性（如果组件没有被拉伸，或者至少不是双向拉伸，那么它应该位于其单元格内的哪个位置）
• 我通常更喜欢使用 insets 而不是 padding，因此，我更喜欢 insets 而不是 ipadx/ipady（应该在组件周围或组件内部添加额外的空白）

Answer 2

您想使用GridBagConsraints#anchor 来定义单元格内要将组件对齐到的位置。

要允许组件跨越多个单元格，您需要使用 GridBagConstraints#gridwidth 和 GridBagConstraints#gridheight（默认为 1）

public class TestLayout09 {

    public static void main(String[] args) {
        new TestLayout09();
    }

    public TestLayout09() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new LayoutPane());
                frame.setBackground(Color.WHITE);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public class LayoutPane extends JPanel {

        public LayoutPane() {
            Border outline = BorderFactory.createLineBorder(Color.black);
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();

            // I'm not sure this really is what you want, but I may be mistaken
//            gbc.weighty = 1.0;
//            gbc.weightx = 1.0;

            JLabel unitLbl = new JLabel("Unit");
            unitLbl.setBorder(outline);
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.ipadx = 30;
            gbc.ipady = 10;
            gbc.anchor = GridBagConstraints.WEST;
            add(unitLbl, gbc);

            JLabel typeLbl = new JLabel("Type");
            typeLbl.setBorder(outline);
            gbc.gridx = 0;
            gbc.gridy = 1;
            gbc.ipadx = 30;
            gbc.ipady = 10;
            add(typeLbl, gbc);

            JTextField unitField = new JTextField();
            typeLbl.setBorder(outline);
            gbc.gridx = 1;
            gbc.gridy = 0;
            gbc.ipadx = 30;
            gbc.ipady = 10;
            gbc.anchor = GridBagConstraints.EAST;
            add(unitField, gbc);

            String[] type = {"All", "Verb", "Noun", "Adjective"};
            JComboBox<String> comboBox = new JComboBox<String>(type);
            gbc.gridx = 1;
            gbc.gridy = 1;
            gbc.ipadx = 30;
            gbc.ipady = 10;
            add(comboBox, gbc);

            JButton btn = new JButton("Test");
            gbc.gridx = 3;
            gbc.gridy = 0;
            gbc.fill = GridBagConstraints.BOTH;
            gbc.gridheight = 2;
            add(btn, gbc);
        }
    }
}

Answer 3

一些答案​​：

将 unitlbl 的锚点放在 WEST。

gbc.anchor = GridBagConstraints.WEST;

还有 unitField 到 EAST 的锚点。

gbc.anchor = GridBagConstraints.EAST;

对于按钮：

JButton button = new JButton("Test");
gbc.fill = GridBagConstraints.VERTICAL;
gbc.gridx = 3;
gbc.gridy = 0;
gbc.gridwidth = 1;
gbc.gridheight = 2;
gbc.weighty = 1;
pane.add(button, gbc);