如何使用 GridBagLayout 在多列上拉伸组件？

Question

I've been learning about layouts in Java Swing and am currently making a simple calculator. I will be using a text field for input/output and I want to stretch it over 2 columns(i am using three total) but when I try to stretch it, it resizes items in the first column. Here's the code and a screenshot.

Screenshot of the app:

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

import javax.swing.*;

public class Calculator extends JFrame{

    JButton but1, but2, but3, but4, but5, but6,
        but7, but8, but9, but0, butPlus, butMinus,
        clearAll;

    JTextField textResult;

    int num1, num2;

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

    public Calculator(){
            
        this.setSize(400,400);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setTitle("Calculator");
    
        JPanel thePanel = new JPanel();
    
        thePanel.setLayout(new GridBagLayout());
    
        GridBagConstraints gridConstraints = new GridBagConstraints();
    
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 0;
        gridConstraints.gridwidth = 1;
        gridConstraints.gridheight = 1;
        gridConstraints.weightx = 50;
        gridConstraints.weighty = 100;
        gridConstraints.insets = new Insets(5, 5, 5, 5);
        gridConstraints.anchor = GridBagConstraints.CENTER;
        gridConstraints.fill = GridBagConstraints.BOTH;
    
        textResult = new JTextField("0", 20);
    
        Font font = new Font("Helvetica", Font.PLAIN, 18);
        textResult.setFont(font);
    
        but1 = new JButton("1");
        but2 = new JButton("2");
        but3 = new JButton("3");
        but4 = new JButton("4");
        but5 = new JButton("5");
        but6 = new JButton("6");
        but7 = new JButton("7");
        but8 = new JButton("8");
        but9 = new JButton("9");
        butPlus = new JButton("+");
        but0 = new JButton("0");
        butMinus = new JButton("-");
        clearAll = new JButton("C");
    
        thePanel.add(clearAll, gridConstraints);
        gridConstraints.gridx = 1;
        gridConstraints.gridwidth = 2;
    
        thePanel.add(textResult, gridConstraints);
        gridConstraints.gridwidth = 1;
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 1;
        thePanel.add(but1, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but2, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(but3, gridConstraints);
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 2;
        thePanel.add(but4, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but5, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(but6, gridConstraints);
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 3;
        thePanel.add(but7, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but8, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(but9, gridConstraints);
        gridConstraints.gridx = 0;
        gridConstraints.gridy = 4;
        thePanel.add(butPlus, gridConstraints);
        gridConstraints.gridx = 1;
        thePanel.add(but0, gridConstraints);
        gridConstraints.gridx = 2;
        thePanel.add(butMinus, gridConstraints);
    
    
        this.add(thePanel);
    
        this.setVisible(true);
    }
}

Answer 1

Note:

Swing offsets/indexes start at 0.

Normally when people use the GridBagLayout the gridx/gridy would start at 0.

However, I see that you are using gridx/gridy with starting values of 1. This should work. It will just mean that column 0 and row 0 will have a size of 0.

To be consistent with how most people use the GridBagLayout, you may want to change your code to use 0 as the starting offset for gridx/gridy.

My advice below assumes you will convert your code to use 0 as the offsets for the grids.

gridConstraints.gridx = 5;
gridConstraints.gridwidth = 20;
thePanel.add(textResult, gridConstraints);

You only have 3 columns. You can't just randomly give a component:

1. a gridx of 5, it can only be 0, 1, 2. In this case you want 1
2. a gridwidth of 20, it can only be 1, 2, 3. In this case you want 2.

If you keep 1 as the starting grid offset then you would need to use 2 for the gridx.

Edit:

it resizes items in the first column

I think the issue is the following:

textResult = new JTextField("0", 20);

The 20 tells the text field to size itself to display 20 "W" characters (which makes the text field large relative to the buttons.

Therefore the buttons in columns 1 and 2 will be half the size of the text field.

Maybe try:

textResult = new JTextField("0", 10);

to see if that is any better.

Or maybe a better option is to just use:

textResult = new JTextField("0");

Now the size of the text field will be controlled by the size of the buttons.

Answer 2

Change the line

textResult = new JTextField("0", 20);

to

textResult = new JTextField("0");

The problem was that your text field has a minimum width that is larger than 2 of your columns combined so it's stretching the 2 columns which stretch everything else.