Java GridBagLayout 上的组件定位

Question

我正在尝试使用 GridBagLayout 在 JPanel 上定位组件，但我得到的输出与我的预期完全不同。希望通过 Whosebug 中的 brilliant-minded ppl 获得一些清晰度:)。

下面我提供了一段代码和程序截图。我的问题是：

为什么 JLabel Choose measure system to convert 不在 Y-axis = 1 上？据我所知，c.gridy=1 向下一个像素，但标签卡在顶部，框架标题没有留下 space。而且，为什么它的位置如此奇怪，即不在中心，也不在开始？
为什么ComboBox和From...和To...之间有这么大的space，而没有space组合框 To... 和 TextField Enter value here...?

代码如下：

    JPanel container = new JPanel();
    container.setLayout(new GridBagLayout());
    getContentPane().add(container, BorderLayout.NORTH);
    TitledBorder outputCenter;
    GridBagConstraints c = new GridBagConstraints();

    label = new JLabel("Choose measure system to convert");
    label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
    c.gridx = 0;
    c.gridy = 1;
    container.add(label, c);

    fromList = new JComboBox<String>(convertFrom); 
    c.gridx = 0;
    c.gridy = 2;
    container.add(fromList, c);

    toList = new JComboBox<String>(convertTo);
    c.gridx = 1;
    c.gridy = 2;
    container.add(toList, c);

    //Field where user enters the value to be converted
    input = new JTextField("Enter value here...");
    input.setPreferredSize(new Dimension(150,30));;
    input.setEditable(true);
    input.setBackground(Color.WHITE);
    input.setBorder(BorderFactory.createLineBorder(Color.BLACK));
    input.addMouseListener(new MouseAdapter(){
        public void mouseClicked(MouseEvent e){
            input.setText("");}});
    c.gridx = 2;
    c.gridy = 2;
    container.add(input, c);

这是屏幕截图：

编辑：如果我更改代码：

    label = new JLabel("Choose measure system to convert");
    label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
    c.gridx = 0; 
    c.gridy = 1;
    container.add(label, c);

    label = new JLabel("Choose measure system to convert");
    label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
    c.gridx = 1; // changed this line
    c.gridy = 1;
    container.add(label, c);

结果是这样的：

这让我很困惑，为什么改变一个组件的位置会影响一切？

Answer 1

GridBagConstraints 将框架设置为有效的网格。默认情况下，网格中单元格的宽度和高度由单元格中数据的大小决定，除非另有说明。因此，如果您想添加一些 space in-between 个单元格，我建议使用 ipadx 和 ipady。您还可以利用 anchor 调整单元格中的数据。我还建议 weightx 和 weighty 来调整实际的单元格大小。

想象一下您当前的设置是这样的：

编辑：您的新 GBC 外观示例。数字是 (gridx,gridy)

Answer 2

Why the JLabel Choose measure system to convert is not on Y-axis = 1? As to my knowledge, c.gridy=1 is one pixel downward

你自己弄糊涂了，c.gridy = 1 不是将它向下定位 1 个像素，而是在下一行，但由于没有前一行，所以它位于第一行。供参考，请参阅：GridBagConstraints#gridy，内容如下：

Specifies the cell at the top of the component's display area, where the topmost cell has gridy=0. The value RELATIVE specifies that the component be placed just below the component that was added to the container just before this component was added.

下一题：

And also, why is it positioned so weird, i.e., not really in the center, nor in the start?

它以自己的单元格为中心，如果您想将它以 JFrame 为中心，那么您可能需要自己创建它 gridx = 1 并将其余组件放在另一个单元格上一个（0 和 2）或根据您希望它看起来像使其跨越 2 列或更多列...

Why is there such a big space between ComboBoxes From... and To..., but there is no space between ComboBox To... and TextField Enter value here...?

这是因为第一个单元格上的大文本，你的程序给了它所有额外的space...

你可以有这样的东西：

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class GridBagLayoutExample {
    private JFrame frame;
    private JPanel pane;
    private JLabel label;
    private JTextField field;
    private JComboBox<String> box1;
    private JComboBox<String> box2;
    private GridBagConstraints gbc;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new GridBagLayoutExample()::createAndShowGui);
    }

    private void createAndShowGui() {
        frame = new JFrame(getClass().getSimpleName());

        pane = new JPanel();
        pane.setLayout(new GridBagLayout());

        gbc = new GridBagConstraints();

        label = new JLabel("Choose measure system to convert");

        box1 = new JComboBox<>(new String[] {"From..."});
        box2 = new JComboBox<>(new String[] {"To..."});

        field = new JTextField(10);

        gbc.insets = new Insets(5, 5, 5, 5); //We add extra space at top, left, bottom, right of each component

        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 3; //We make our text to span 3 cells
        pane.add(label, gbc);

        gbc.gridy = 1;
        gbc.gridwidth = 1; //We return the spanning to 1 single cell
        pane.add(box1, gbc);

        gbc.gridx = 1;
        pane.add(box2, gbc);

        gbc.gridx = 2;
        pane.add(field, gbc);

        frame.add(pane);
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

产生以下输出：

Java GridBagLayout 上的组件定位

Java component positioning on GridBagLayout

java

swing

layout-manager

gridbaglayout