嵌套布局 - BoxLayout 内的 FlowLayout

Question

我有一个controlPanel (BoxLayout)：

controlPanel.setLayout(new BoxLayout(controlPanel, BoxLayout.Y_AXIS));

现在我构建两个FlowLayout 并将它们添加到contolPanel 面板：

JPanel fromDatePanel = new JPanel(new FlowLayout());
JPanel untilDatePanel = new JPanel(new FlowLayout());

fromDatePanel.add(new JLabel("From - "));
fromDatePanel.add(new JButton("..."));
untilDatePanel.add(new JLabel("Until - "));
untilDatePanel.add(new JButton("..."));

controlPanel.add(fromDatePanel);
controlPanel.add(untilDatePanel);

我明白了：

为什么它会在布局之间产生间隙？例如，如果我插入一个JButton，它可以正常工作（它插入它们时没有间隙）。

如何消除两个FlowLayout 之间的差距？ （所以它会像蓝色的差距）

Answer 1

您可以使用GridBagLayout 实现垂直布局（垂直居中）（并使用GridBagConstraint 和gridwidth=REMAINDER）：

import java.awt.FlowLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class TestGridBagLayout {

    protected void initUI() {
        JFrame frame = new JFrame();
        JPanel controlPanel = (JPanel) frame.getContentPane();
        controlPanel.setLayout(new GridBagLayout());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;

        JPanel fromDatePanel = new JPanel(new FlowLayout());
        JPanel untilDatePanel = new JPanel(new FlowLayout());

        fromDatePanel.add(new JLabel("From - "));
        fromDatePanel.add(new JButton("..."));
        untilDatePanel.add(new JLabel("Until - "));
        untilDatePanel.add(new JButton("..."));

        controlPanel.add(fromDatePanel, gbc);
        controlPanel.add(untilDatePanel, gbc);
        frame.setSize(600, 600);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                TestGridBagLayout testMultiplePanels = new TestGridBagLayout();
                testMultiplePanels.initUI();

            }
        });
    }

}

关于JButton 和JPanel 添加到BoxLayout 时的区别，这是由于getMaximumSize() 的实现方式不同，BoxLayout 已将其考虑在内。 JButton 返回首选大小，而 JPanel 将返回 null，BoxLayout 将其解释为无限维度。

如果你想保留你的BoxLayout，你可以覆盖JPanel.getMaximumSize()并返回getPreferredSize()：

import java.awt.Dimension;
import java.awt.FlowLayout;

import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class TestGridBagLayout {

    protected void initUI() {
        JFrame frame = new JFrame();
        JPanel controlPanel = (JPanel) frame.getContentPane();
        controlPanel.setLayout(new BoxLayout(controlPanel, BoxLayout.Y_AXIS));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel fromDatePanel = new JPanel(new FlowLayout()) {
            @Override
            public Dimension getMaximumSize() {
                return getPreferredSize();
            }
        };
        JPanel untilDatePanel = new JPanel(new FlowLayout()) {
            @Override
            public Dimension getMaximumSize() {
                return super.getMaximumSize();
            }
        };

        fromDatePanel.add(new JLabel("From - "));
        fromDatePanel.add(new JButton("..."));
        untilDatePanel.add(new JLabel("Until - "));
        untilDatePanel.add(new JButton("..."));

        controlPanel.add(fromDatePanel);
        controlPanel.add(untilDatePanel);
        frame.setSize(600, 600);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                TestGridBagLayout testMultiplePanels = new TestGridBagLayout();
                testMultiplePanels.initUI();

            }
        });
    }

}

Answer 2

关于Box.createVerticalGlue()，请参阅Using Invisible Components as Filler。

Answer 3

我使用了BorderLayout，它成功了。

        JPanel controlPanel = new JPanel();
        //  controlPanel.setLayout(new BoxLayout(controlPanel, BoxLayout.Y_AXIS));
        controlPanel.setLayout(new BorderLayout());

        JPanel fromDatePanel = new JPanel(new FlowLayout());
        JPanel untilDatePanel = new JPanel(new FlowLayout());

        fromDatePanel.add(new JLabel("From - "));
        fromDatePanel.add(new JButton("..."));
        untilDatePanel.add(new JLabel("Until - "));
        untilDatePanel.add(new JButton("..."));

        controlPanel.add(fromDatePanel, BorderLayout.NORTH);
        controlPanel.add(untilDatePanel, BorderLayout.CENTER);

Edit-1：

您可以在每个面板内添加嵌套面板。

        JPanel controlPanel = new JPanel();
        controlPanel.setLayout(new BoxLayout(controlPanel, BoxLayout.Y_AXIS));
        // controlPanel.setLayout(new BorderLayout());

        JPanel fromDatePanel = new JPanel(new FlowLayout());
        JPanel untilDatePanel = new JPanel(new FlowLayout());
        JPanel thirdPnl = new JPanel(new FlowLayout());
        JPanel fourthPnl = new JPanel(new FlowLayout());

        JPanel thrdForthPnl = new JPanel(new BorderLayout()); 

        fourthPnl.add(new JLabel("Fourth"));
        fourthPnl.add(new JButton("4.1"));

        thirdPnl.add(new JLabel("Third"));
        thirdPnl.add(new JButton("3.1"));

        thrdForthPnl.add(thirdPnl, BorderLayout.NORTH);
        thrdForthPnl.add(fourthPnl, BorderLayout.CENTER);

        fromDatePanel.add(new JLabel("From - "));
        fromDatePanel.add(new JButton("..."));
        untilDatePanel.add(new JLabel("Until - "));
        untilDatePanel.add(new JButton("..."));

        controlPanel.add(fromDatePanel, BorderLayout.NORTH);
        controlPanel.add(untilDatePanel, BorderLayout.CENTER);
        controlPanel.add(thrdForthPnl, BorderLayout.SOUTH);