Java Swing：JButtons 和 JSliders 将无法单独工作

Question

我在 Java 中使用 Swing 制作 UI 还比较陌生，我在让按钮和滑块在我的项目中工作时遇到了问题。我试图测试我的滑块和按钮是否适用于印刷品，但发现它们不起作用。

如果我不检查与 slider/button 交互的内容，我将得到结果。 IE。如果按下项目中的任何滑块或按钮，我只会得到结果。但显然我希望他们都做不同的事情。

到目前为止，这是我的代码

Main.java

//Imports here, just saving space

public class Main
{
    public static void main(String[] args) throws IOException
    {
        ImageProcessor e = new ImageProcessor();
        e.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        e.initGUI();
    }
}

ImageProcessor.java

import java.awt.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.event.*;

public class ImageProcessor extends JFrame
{

    JPanel          imagePane;
    JCheckBox       xView, yView, zView, mip;
    JLabel          xSliceLabel, ySliceLabel, zSliceLabel;
    JSlider         xSliceSlider, ySliceSlider, zSliceSlider;
    JLabel          xImageIcon, yImageIcon, zImageIconl;
    BufferedImage   xImage, yImage, zImage;
    short           cthead[][][];
    short           min, max;
    double          ai, aj, ak;
    JButton         test;


    public void initGUI()
    {
        // Build the window to contain everything
        setTitle("Simple Example");
        setSize(1200, 900);

        /////// MAKE THE GUI ///////


        // Container Window
        Container container = getContentPane();
        container.setLayout(null);


        // Check boxes to select view
        JCheckBox xView = new JCheckBox("X View");
        xView.setBounds(150, 45, 65, 20);
        container.add(xView);

        JCheckBox yView = new JCheckBox("Y View");
        yView.setBounds(225, 45, 65, 20);
        container.add(yView);

        JCheckBox zView = new JCheckBox("Z View");
        zView.setBounds(300, 45, 65, 20);
        container.add(zView);


        // Panel to show CT Head image
        JPanel imagePane = new JPanel();
        imagePane.setBounds(25, 75, 512, 512);
        imagePane.setBorder(BorderFactory.createTitledBorder("Image View"));
        container.add(imagePane);

        // Image labels to display BufferedImages
        JLabel xImageIcon = new JLabel();
        imagePane.add(xImageIcon);



        // Checkbox for MIP on/off
        JCheckBox mip = new JCheckBox("MIP");
        mip.setBounds(125, 630, 65, 20);
        container.add(mip);


        // Slider labels
        JLabel xSliceLabel = new JLabel("X Slice");
        xSliceLabel.setBounds(50, 675, 60, 25);
        container.add(xSliceLabel);

        JLabel ySliceLabel = new JLabel("Y Slice");
        ySliceLabel.setBounds(50, 725, 60, 25);
        container.add(ySliceLabel);

        JLabel zSliceLabel = new JLabel("Z Slice");
        zSliceLabel.setBounds(50, 775, 60, 25);
        container.add(zSliceLabel);


        // Slice sliders
        JSlider xSliceSlider = new JSlider(0, 255, 76);
        xSliceSlider.setBounds(125, 675, 256, 25);
        container.add(xSliceSlider);

        JSlider ySliceSlider = new JSlider(0, 255, 76);
        ySliceSlider.setBounds(125, 725, 256, 25);
        container.add(ySliceSlider);

        JSlider zSliceSlider = new JSlider(0, 112, 76);
        zSliceSlider.setBounds(125, 775, 256, 25);
        container.add(zSliceSlider);

        JButton test = new JButton("Test");
        test.setBounds(50, 700, 60, 25);
        container.add(test);

        // Handler class
        GUIEventHandler handler = new GUIEventHandler();

        xSliceSlider.addChangeListener(handler);
        ySliceSlider.addChangeListener(handler);
        zSliceSlider.addChangeListener(handler);

        test.addActionListener(handler);


        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);

    }

    private class GUIEventHandler implements ActionListener, ChangeListener
    {
        public void stateChanged(ChangeEvent e)
        {
            if (e.getSource() == xSliceSlider)
            {
                System.out.println("x Slider changed!");

            } else if (e.getSource() == ySliceSlider)
            {
                System.out.println("y Slice changed!");

            } else if (e.getSource() == zSliceSlider)
            {
                System.out.println("Z slice changed!");
            }

            //This will work if any of the sliders change state
            //System.out.println("Something changed");
        }

        public void actionPerformed(ActionEvent e)
        {
            if (e.getSource() == test)
            {
                System.out.println("Testing...");
            }

            //This will also work if any button is pressed
            //System.out.println("Testing again...");
        }
    }
}

非常感谢任何知识渊博的人看到这个并指出我正确的方向。

非常感谢大家！

Answer 1

您定义了：

按钮和滑块字段
同名局部变量

在处理程序中，您访问字段，但它们从未被初始化！

在initGUI中重写一些行：

JSlider xSliceSlider = new JSlider(0, 255, 76); // define a local variable

如：

xSliceSlider = new JSlider(0, 255, 76); // initialize the field

Answer 2

我敢打赌这不是您的 GUI 在计算机中的样子...是吗？

文本被裁剪了，但是...为什么？您可能想知道。

嗯，那是因为您使用了 null-layout 并手动设置了每个组件的边界及其大小。

但是...我该如何解决这个问题？

首先是一些背景阅读：Null layout is evil, Why is it frowned upon to use a null layout in Swing?,

现在，对于您的实际问题，您可以按照@MadProgrammer 对 this question 的回答，他说：

Realistically, if you can, you should be giving each slider it's own listener and dealing with it directly from the source...
JSlider slider = new JSlider();
slider.addChangeListener(new ChangeListener() {
    public void stateChanged(ChangeEvent e) {
        JSlider slider= (Slider)e.getSource();
        // Do funky stuff
    }
});

按照上述提示，您可以按如下方式修复您的 GUI，让 Layout managers 为您处理 window 大小，这样 GUI 在每台计算机上看起来都正确，例如：

import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingConstants;
import javax.swing.SwingUtilities;

public class ImageProcessingCorrected {
    private JFrame frame;

    private JPanel pane;
    private JPanel imagePane;
    private JPanel boxesPane;
    private JPanel controlsPane;
    private JPanel slidersPane;

    private JCheckBox[] boxes;

    private JButton button;

    private JCheckBox mipBox;

    private JSlider[] sliders;

    private static final String[] AXIS = new String[] {"X", "Y", "Z"};

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

    @SuppressWarnings("serial")
    private void createAndShowGui() {
        frame = new JFrame(getClass().getSimpleName());

        pane = new JPanel();
        imagePane = new JPanel() {
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(200, 400);
            }
        };
        boxesPane = new JPanel();
        controlsPane = new JPanel();
        slidersPane = new JPanel();

        mipBox = new JCheckBox("MIP");

        button = new JButton("Test");
        button.addActionListener(e -> {
            System.out.println("Test button pressed!");
        });

        pane.setLayout(new BoxLayout(pane, BoxLayout.PAGE_AXIS));
        boxesPane.setLayout(new GridLayout(1, 3));
        slidersPane.setLayout(new GridLayout(3, 2, 5, 15));

        boxes = new JCheckBox[3];
        sliders = new JSlider[3];

        for (int i = 0; i < boxes.length; i++) {
            boxes[i] = new JCheckBox(AXIS[i] + " View");
            boxes[i].setHorizontalAlignment(SwingConstants.CENTER);
            boxesPane.add(boxes[i]);
        }

        for (int i = 0; i < sliders.length; i++) {
            sliders[i] = new JSlider(0, 100, 50);
            sliders[i].setName(AXIS[i] + " Slice");
            JLabel label = new JLabel(AXIS[i] + " Slice");
            label.setHorizontalAlignment(SwingConstants.CENTER);

            sliders[i].addChangeListener(e -> {
                System.out.println(((JSlider) e.getSource()).getName() + " changed!");
            });

            slidersPane.add(label);
            slidersPane.add(sliders[i]);
        }

        controlsPane.add(mipBox);
        controlsPane.add(button);

        imagePane.setBorder(BorderFactory.createTitledBorder("Image View"));

        pane.add(boxesPane);
        pane.add(imagePane);
        pane.add(controlsPane);
        pane.add(slidersPane);

        frame.add(pane);

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

这是 sysout 调用打印的示例：

X Slice changed!
X Slice changed!
X Slice changed!
Y Slice changed!
Y Slice changed!
Y Slice changed!
Y Slice changed!
Z Slice changed!
Z Slice changed!
Z Slice changed!
Z Slice changed!
Test button pressed!

Answer 3

而不是对多个 GUI 对象使用同一个事件处理程序为每个 GUI 对象使用单独的事件处理程序是很常见的。这通常是通过匿名 classes 实现事件侦听器接口来完成的。

在您的应用程序中，您将替换您的代码

    // Handler class
    GUIEventHandler handler = new GUIEventHandler();

    xSliceSlider.addChangeListener(handler);
    ySliceSlider.addChangeListener(handler);
    zSliceSlider.addChangeListener(handler);

    test.addActionListener(handler);

通过此代码

    xSliceSlider.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            System.out.println("x Slider changed!");
        }
    });
    ySliceSlider.addChangeListener(new ChangeListener() {     
        @Override
        public void stateChanged(ChangeEvent e) {
            System.out.println("y Slider changed!");
        }
    });
    zSliceSlider.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            System.out.println("z Slider changed!");
        }
    });

    test.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("Testing...");
        }
    });

这样做你就不再需要 GUIEventHandler class，并且事件处理方法中不需要检查e.getSource()。

顺便说一句：如果你是运行 Java 8+ 你可以更简洁地重写上面的代码通过使用 lambda expressions 作为事件处理程序：

    xSliceSlider.addChangeListener(e -> {
        System.out.println("x Slider changed!");
    });
    ySliceSlider.addChangeListener(e -> {     
        System.out.println("y Slider changed!");
    });
    zSliceSlider.addChangeListener(e -> {
        System.out.println("z Slider changed!");
    });
    test.addActionListener(e -> {
        System.out.println("Testing...");
    });

Java Swing：JButtons 和 JSliders 将无法单独工作

Java Swing: JButtons and JSliders will not work individually

java

swing

actionlistener

changelistener

eventhandler