JCheckBox没有出现

Question

我已经在任何地方检查了修复但没有任何方法可以使我的复选框显示。我将它添加到面板并将面板添加到窗口。按钮出现所以它必须是复选框的问题。这是我的代码：

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.KeyEvent;

import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class MainApplication {

    public static Toolkit tk = Toolkit.getDefaultToolkit();

    public static void main(String[] args) {
        MainApplication instance = new MainApplication();
        instance.start();
    }

    private JFrame window;
    private JPanel mainPanel;
    private JPanel contingencyPanel;

    private JButton applyButton = new JButton("Apply Changes");
    private JCheckBox autoRedLightBox = new JCheckBox("Red Light");
    private JCheckBox autoYellowLightBox = new JCheckBox("Yellow Light");
    private JCheckBox autoGreenLightBox = new JCheckBox("Green Light");
    private JCheckBox autoBlueLightBox = new JCheckBox("Blue Light");

    public void start() {
        window = new JFrame("Main Control Window");
        mainPanel = new JPanel();
        contingencyPanel = new JPanel();

        window.setSize(1280, 720);
        window.setResizable(false);
        window.setFocusable(true);
        window.setFocusTraversalKeysEnabled(true);
        int screenWidth = (int)tk.getScreenSize().getWidth();
        int screenHeight = (int)tk.getScreenSize().getHeight();
        window.setLocation((screenWidth/2)-(window.getWidth()/2), (screenHeight/2)-(window.getHeight()/2));
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        mainPanel.setLayout(null);
        contingencyPanel.setLayout(null);

        applyButton.setToolTipText("Changes will be applied to the arduino.");
        applyButton.setSize(new Dimension(120, 30));
        applyButton.setLocation(new Point((1280-120)-10, (720-56)-10));

        autoRedLightBox.setSelected(true);
        autoRedLightBox.setLocation(new Point(30, 30));
        autoRedLightBox.setMnemonic(KeyEvent.VK_R);

        mainPanel.add(applyButton);
        mainPanel.add(autoRedLightBox, BorderLayout.CENTER);

        window.add(mainPanel);
        window.setVisible(true);
    }
}

期望的结果：

Answer 1

这非常适合GridLayout。

import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

public class ButtonsAndChecks {

    private JComponent ui = null;

    ButtonsAndChecks() {
        initUI();
    }

    public void initUI() {
        if (ui!=null) return;

        // adjust last two numbers to need..
        ui = new JPanel(new GridLayout(0,5,20,20));
        ui.setBorder(new EmptyBorder(4,4,4,4));

        // adjust numbers to need..
        for (int i=1; i<26; i++) {
            ui.add(new JButton("Button " + i));
        }
        // adjust numbers to need..
        for (int i=1; i<26; i++) {
            ui.add(new JCheckBox("Check " + i, i%2==0));
        }
    }

    public JComponent getUI() {
        return ui;
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception useDefault) {
                }
                ButtonsAndChecks o = new ButtonsAndChecks();

                JFrame f = new JFrame(o.getClass().getSimpleName());
                f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                f.setLocationByPlatform(true);

                f.setContentPane(o.getUI());
                f.pack();
                f.setMinimumSize(f.getSize());

                f.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}

Answer 2

在Swing中阅读一下有关LayoutManagers的内容。每个面板都需要一个布局来保存组件，如果您没有为JPanel指定布局，则使用默认布局（FlowLayout）。 当你为布局

设置null时，问题出在这一行

    mainPanel.setLayout(null);

只需对其进行评论，您就会看到表单上的按钮。 此外，要将表单放在屏幕中心，您可以调用此方法

    window.setLocationRelativeTo(null);