在循环内的 JscrollPane 内添加标签

Question

我有一个循环生成一些标题和描述，它们是字符串值，我制作了标签以包含这两个字符串，我想将它们添加到 JScrollPane，但由于某种原因我的代码不起作用，我'现在没有收到任何错误，滚动窗格中没有添加任何项目，这是我的代码：

package testa;

import java.awt.Color;
import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class test extends JFrame {

    JLabel[] titles;
    JLabel[] descriptions;
    JPanel[] panels;
    JScrollPane jScrollPane1 = new JScrollPane();
    JPanel bigPanel = new JPanel();

    public test() {
        this.setLocationRelativeTo(null);
        this.setSize(1000, 500);
        this.jScrollPane1.setSize(1000, 500);

        this.getContentPane().add(this.jScrollPane1);

        this.setVisible(true);
        requetezQuery();
    }

    public void requetezQuery() {
        int resultsList = 10;
        this.titles = new JLabel[resultsList];
        this.descriptions = new JLabel[resultsList];
        this.panels = new JPanel[resultsList];
        for (int i = 0; i < resultsList; i++) {

            String title = "Test Title " + i;
            String resume = "Test Resume " + i;

            this.titles[i] = new JLabel();
            this.descriptions[i] = new JLabel();
            this.panels[i] = new JPanel();
            this.panels[i].setLayout(new FlowLayout());
            this.titles[i].setText(title);
            this.descriptions[i].setText(resume);
            this.titles[i].setForeground(Color.red);
            this.descriptions[i].setForeground(Color.red);
            this.panels[i].add(this.titles[i]);
            this.panels[i].add(this.descriptions[i]);
            this.bigPanel.add(panels[i]);
        }
        this.jScrollPane1.add(this.bigPanel);
    }

    public static void main(String args[]) {
        test a = new test();
    }
}

我尝试 System.out.println 标题和简历变量及其工作，所以问题不在于它们。

Answer 1

我做了一些更正以使您的代码正常工作，并添加了 cmets 来解释需要做什么：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridLayout; 
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class Test extends JFrame{ //see https://www.javatpoint.com/java-naming-conventions

    private JLabel[] titles;
    private JLabel[] descriptions;
    private JPanel [] panels;
    private JScrollPane jScrollPane1;
    private JPanel bigPanel;
    private final static int NUM_OF_RESULTS =10;

    public Test() {

        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //this.setSize(1000,500);             no need to set size. use preferred sizes
        //jScrollPane1.setSize(1000, 500);    and layouts. see following comments

        bigPanel = new JPanel();
        //set layout to
        GridLayout layout = new GridLayout(NUM_OF_RESULTS, 0);
        bigPanel.setLayout(layout);
        jScrollPane1 = new JScrollPane(bigPanel);
        getContentPane().add(jScrollPane1);

        requetezQuery();
        pack(); //see https://stackoverflow.com/questions/22982295/what-does-pack-do
        setVisible(true); //set visible typically comes last
    }
    public void requetezQuery(){

        titles = new JLabel[NUM_OF_RESULTS];
        descriptions = new JLabel[NUM_OF_RESULTS];
        panels = new JPanel[NUM_OF_RESULTS];

        for(int i = 0; i<NUM_OF_RESULTS; i++){

            String title="Test Title "+i;
            String resume="Test Resume "+i;

            titles[i]= new JLabel();
            descriptions[i]= new JLabel();
            panels[i]= new JPanel();
            panels[i].setPreferredSize(new Dimension(250, 50));
            panels[i].setLayout(new FlowLayout()); //FlowLayout is default for JPanel
            titles[i].setText(title);
            descriptions[i].setText(resume);
            titles[i].setForeground(Color.red);
            descriptions[i].setForeground(Color.red);
            panels[i].add(titles[i]);
            panels[i].add(descriptions[i]);
            bigPanel.add(panels[i],i, 0);
        }
    }

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

代码可以进一步改进。我尽量减少更改，希望它能让您更容易看到更改。
如有需要，请随时要求澄清。

Answer 2

一个问题是您试图将组件直接添加到 JScrollPane 中，而 JScrollPane 不是组件应该去的地方。相反，这些组件属于视口的视图，即 JScrollPane 正在显示的组件。

建议：

• 创建一个表示此视图的 JPanel，并将其添加到 JScrollPane 的视口中。
• 给这个 JPanel 一个合适的布局，以便它能够正确显示添加到其中的组件
• 在上面的代码中，将组件添加到此 JPanel，然后重新验证并重新绘制它，以便其布局管理器布局组件并正确绘制它们。
• 或者更好更简洁，将表格数据添加到由 JScrollPane 保存的 JTable 中

例如，下面的代码将一对 JLabel 添加到一个 innerPanel JPanel，其中一个使用 BorderLayout 将一个标签放置在左侧和另一个中心。 然后，它将这个 innerPanel 放置到另一个 JPanel viewportViewPanel 中，该 JPanel 使用 GridLayout 将 innerPanel 放置在单列多行网格中。通过将 viewportViewPanel 传递给 JScrollPane 的构造函数，将其放置在 JScrollPane 的视口中。请注意，我们从不在 JScrollPane 上调用 .add(...)：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import javax.swing.*;

public class MyTest extends JPanel {
    private static final int COUNT = 400;
    private JPanel viewportViewPanel = new JPanel();
    private JScrollPane scrollPane = new JScrollPane(viewportViewPanel);

    public MyTest() {
        setPreferredSize(new Dimension(800, 500));
        viewportViewPanel.setLayout(new GridLayout(0, 1));
        for (int i = 0; i < COUNT; i++) {
            String text = "abcd efgh ijkl mnop qrst uvwx";
            text = String.format("%s %s %s", text, text, text);
            JPanel innerPanel = new JPanel();
            innerPanel.setBorder(BorderFactory.createLineBorder(Color.BLUE));
            innerPanel.setLayout(new BorderLayout());
            innerPanel.add(new JLabel("Test Title:"), BorderLayout.LINE_START);
            innerPanel.add(new JLabel(text, SwingConstants.CENTER));
            viewportViewPanel.add(innerPanel);
        }

        setLayout(new BorderLayout());
        add(scrollPane);
    }

    private static void createAndShowGui() {
        MyTest mainPanel = new MyTest();

        JFrame frame = new JFrame("MyTest");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

更好的是，如果您希望显示标题和描述，请考虑仅在 JList 中显示标题，并在 JTextArea 中显示所选 JList 项的描述。像这样：

import java.awt.BorderLayout;

import javax.swing.*;

@SuppressWarnings("serial")
public class ShowTitleDescriptions extends JPanel {
    private static final int COUNT = 500;
    // nonsense text as a demo filler
    private static final String LOREM_IPSUM = "Lorem ipsum dolor sit amet, consectetur "
            + "adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore "
            + "magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco "
            + "laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor "
            + "in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla "
            + "pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa "
            + "qui officia deserunt mollit anim id est laborum.";
    private DefaultListModel<TitleDescription> listModel = new DefaultListModel<>();
    private JList<TitleDescription> titlesList = new JList<>(listModel);
    private JTextArea descriptionArea = new JTextArea(20, 60);

    public ShowTitleDescriptions() {
        titlesList.setVisibleRowCount(20);
        JScrollPane titleScroll = new JScrollPane(titlesList);

        descriptionArea.setLineWrap(true);
        descriptionArea.setWrapStyleWord(true);
        descriptionArea.setEditable(false);
        JScrollPane descriptionScroll = new JScrollPane(descriptionArea);

        for (int i = 0; i < COUNT; i++) {
            String title = "Title " + i;
            StringBuilder descriptionSb = new StringBuilder();

            // fill description with random text
            for (int j = 0; j < 40; j++) {
                descriptionSb.append(title + "\n");
                descriptionSb.append(LOREM_IPSUM + " ");
                descriptionSb.append(LOREM_IPSUM + " ");
                descriptionSb.append(LOREM_IPSUM);
                descriptionSb.append("\n\n");
            }
            TitleDescription titleDescr = new TitleDescription(title, descriptionSb.toString());
            listModel.addElement(titleDescr);
        }

        titlesList.addListSelectionListener(l -> {
            TitleDescription selection = titlesList.getSelectedValue();
            descriptionArea.setText(selection.getDescription());
        });
        titlesList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        titlesList.setSelectedIndex(0);

        setLayout(new BorderLayout());
        add(descriptionScroll);
        add(titleScroll, BorderLayout.LINE_END);
    }

    // class to hold title and description together
    private static class TitleDescription {
        private String title;
        private String description;

        public TitleDescription(String title, String description) {
            this.title = title;
            this.description = description;
        }

        public String getTitle() {
            return title;
        }

        public String getDescription() {
            return description;
        }

        // JList uses this to decide what to display
        @Override
        public String toString() {
            return title;
        }

    }

    private static void createAndShowGui() {
        ShowTitleDescriptions mainPanel = new ShowTitleDescriptions();

        JFrame frame = new JFrame("ShowTitleDescriptions");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}