求助：含两个子JPanel的JPanel设置内边距无效（GridBagLayout场景）

问题说明 #

• 现象：红色边框的dataInputPanel无法显示内边距，无报错但设置不生效
• 目标：为dataInputPanel设置上下左右各10的内边距

相关代码 #

Main类代码 #

public class Main {
    public static void main(String[] args) {
        JFrame win = new JFrame();
        win.setTitle("Lord of the Rings - Battle Simulator");
        win.setSize(500, 600);
        win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        win.setLayout(new GridLayout(2, 1));
        win.setResizable(false);
        //-------------

        JPanel dataInputPanel = new JPanel();
        dataInputPanel.setLayout(new GridLayout(1, 2, 10, 0));
        //dataInputPanel.setBackground(Color.RED);
        dataInputPanel.setBorder(new LineBorder(Color.RED, 4, true));

        JPanel battleOutupPanel = new JPanel();
        //battleOutupPanel.setBackground(Color.GREEN);
        battleOutupPanel.setBorder(new LineBorder(Color.GREEN, 4, true));
        //-------------------------------------

        int paddingSize = 50;
        Insets paddingInsets = new Insets(paddingSize, paddingSize, paddingSize, paddingSize);

        // Heroes Data Input Panel - dataInputPanel GridBagLayout 1 row, 2 columns
        JPanel heroesDataInputPanel = new JPanel();
        //heroesDataInputPanel.setBackground(Color.YELLOW);
        heroesDataInputPanel.setBorder(new LineBorder(Color.YELLOW, 4, true));

        GridBagConstraints gbc1 = new GridBagConstraints();
        gbc1.gridx = 0;
        gbc1.gridy = 0;
        gbc1.insets = paddingInsets;
        dataInputPanel.add(heroesDataInputPanel, gbc1);

        // Beasts Data Input Panel - dataInputPanel - GridBagLayout 1 row, 2 columns
        JPanel beastsDataInputPanel = new JPanel();
        //beastsDataInputPanel.setBackground(Color.ORANGE);
        beastsDataInputPanel.setBorder(new LineBorder(Color.ORANGE, 4, true));

        GridBagConstraints gbc2 = new GridBagConstraints();
        gbc2.gridx = 1;
        gbc2.gridy = 0;
        gbc2.insets = paddingInsets;
        dataInputPanel.add(beastsDataInputPanel, gbc2);
        //-------------

        win.add(dataInputPanel);
        win.add(battleOutupPanel);
        win.setVisible(true);
    }
}

Win类代码 #

public class Win extends JFrame {
}

Pnl类代码 #

public class Pnl extends JPanel {
}

界面截图 #

问题原因 #

dataInputPanel设置的布局是GridLayout，但你使用了GridBagConstraints的insets属性来设置内边距——该属性仅在GridBagLayout布局下生效，因此内边距设置无效。

解决方案 #

• 方案一：切换布局为GridBagLayout
  修改dataInputPanel的布局代码：

  dataInputPanel.setLayout(new GridBagLayout());
  

  此时原有的GridBagConstraints.insets设置会正常生效。

• 方案二：使用空边框实现内边距
  若想保留GridLayout，可通过BorderFactory创建复合边框，既保留原有红色边框，又添加内边距：

  // 先保留原有的红色边框，再叠加空边框作为内边距
  dataInputPanel.setBorder(BorderFactory.createCompoundBorder(
      new LineBorder(Color.RED, 4, true),
      BorderFactory.createEmptyBorder(10, 10, 10, 10)
  ));
  

内容的提问来源于stack exchange，提问作者OrlandoVSilva