java - 为什么我无法在 JPanel 上调整 JButton 的大小或重新定位？

Question

package swingtraining;

import static java.awt.Color.BLACK;
import static java.awt.Color.RED;
import java.awt.EventQueue;
import static java.awt.Font.BOLD;
import java.awt.Point;
import java.awt.Rectangle;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JButton;



public class JFrameWithAButton extends JFrame {

public JFrameWithAButton(){

    setSize(400,400);
    setTitle("Swing is hard");
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);

    }

    public static void main(String args[]){

    JPanel Jp1 = new JPanel();

    Jp1.setOpaque(true);

    Jp1.setBackground(RED);

    JButton Jbt = new JButton();

    Jbt.setLayout(null);  
    Jbt.setSize(200,200);

    Jbt.setBounds(new Rectangle(new Point(200, 200)));
    Jbt.setText("Hello!");

    EventQueue.invokeLater(new Runnable(){

        public void run(){

            JFrameWithAButton ex = new JFrameWithAButton();
            ex.setVisible(true); 
            ex.add(Jp1);
            Jp1.add(Jbt);
            }
      });
 }

}

抱歉，如果代码有点像妈妈的意大利面条式的，但我就是无法破解这个 cookie >。> 即使将布局设置为 null，它也不会移动。关于如何让这个 JButton 不仅移动到窗口中间，而且增长 200 x 200 像素，有什么建议吗？

Answer 1

Any suggestions of how I get this JButton to not only move to the middle of the window but also grow 200 by 200 pixels?

我能想到一些，但没有一个使用 null 布局

GridBagConstraints

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.ipadx = 200;
            gbc.ipady = 200;

            add(new JButton("Hello"), gbc);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

    }

}

JButton#setMargin

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();

            JButton btn = new JButton("Hello");
            btn.setMargin(new Insets(100, 100, 100, 100));
            add(btn);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

    }

}

空边框

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;

public class Test {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new BorderLayout());
            setBorder(new EmptyBorder(50, 50, 50, 50));
            JButton btn = new JButton("Hello");
            add(btn);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

    }

}

您可以组合使用它们，也许使用 EmptyBorder 和 GridBagConstraints 来进一步约束布局。

这些示例的最大好处是，在大多数情况下，如果字体大小发生变化或字体的渲染要求发生变化，布局能够进行补偿

避免使用 null 布局，像素完美布局是现代 UI 设计中的一种幻觉。影响组件个体尺寸的因素太多，您无法控制其中任何一个。 Swing 的设计初衷是与布局管理器一起工作，放弃它们将导致无穷无尽的问题，您将花费越来越多的时间来尝试纠正

因为读起来总是很有趣，Why is it frowned upon to use a null layout in SWING?