在Japanel中使用jList的滚动面板不起作用

Question

编辑

这是您的代码，其中projectList的字符串太长，这会使滚动条出现。 但事实并非如此。 而是扩大了框架的大小

import java.awt.BorderLayout;
import javax.swing.*;

public class FooFrame extends JFrame {
private JList jList;
private String[] projectList = {"One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nineeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"};
private DefaultListModel listItems;
private JScrollPane scrollpane;

public FooFrame() {
    JLabel lblHeading = new JLabel(
            " Demo text");
    JPanel mainLayout = new JPanel();
    mainLayout.setLayout(new BorderLayout());
    mainLayout.add(lblHeading, BorderLayout.NORTH);
    jList = new JList(projectList);

    // listItems = new DefaultListModel(); // wasted line since you don't use this
    jList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    scrollpane = new JScrollPane(jList, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
    mainLayout.add(scrollpane); 
    add(mainLayout);
}

private static void createAndShowGui() {
    FooFrame frame = new FooFrame();
    frame.setSize(10,10);
    frame.setResizable(false);
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    frame.pack();
    frame.setLocationByPlatform(true);
    frame.setVisible(true);
}

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

}

当我尝试在Japanel的Jscrollpane中添加JList时，我注意到了一件奇怪的事情。 如果我尝试直接在框架的JscrollPane中添加JList，则很容易做到。 好像我想添加相同的内容放在面板（带有边框布局）中一样，它对我不起作用。

这是示例代码

JLabel lblHeading = new JLabel(
            " Demo text");
    JPanel mainLayout = new JPanel();
    mainLayout.setLayout(new BorderLayout());
    mainLayout.add(lblHeading, BorderLayout.NORTH);
    jList = new JList(projectList);

    listItems = new DefaultListModel();
    jList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    scrollpane = new JScrollPane(jList, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
    mainLayout.add(scrollpane); 
    add(mainLayout);

无论我做什么，JList中的文本都会超出框架，并且不会出现滚动条。

有什么建议么？

Answer 1

您的问题不是问题，而是一个功能-JScrollPane是一个智能组件，除非再次需要它们，否则不会显示滚动条或滚动条选项卡，并且仅当JScrollPane的视口小于它的组件时才会发生保持并显示。 例如，如果您人为地限制了包含JPanel的大小，这是通过覆盖getPreferredSize()来完成的，将显示滚动条选项卡：

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

@SuppressWarnings("serial")
public class FooPanel extends JPanel {
    private static final int PREF_W = 200;
    private static final int PREF_H = 200;
    private static final String[] PROJECT_LIST = { "One", "Two", "Three",
            "FOURRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR" };
    private static final String TITLE_TEXT = "Demo Text";
    private JList<String> jList = new JList<>(PROJECT_LIST);

    public FooPanel() {
        JScrollPane scrollPane = new JScrollPane(jList);
        scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

        setLayout(new BorderLayout());
        add(new JLabel(TITLE_TEXT, SwingConstants.CENTER), BorderLayout.PAGE_START);
        add(scrollPane);
    }

    @Override
    public Dimension getPreferredSize() {
        Dimension superSz = super.getPreferredSize();
        if (isPreferredSizeSet()) {
            return superSz;
        }
        int prefW = Math.min(superSz.width, PREF_W);
        int prefH = Math.max(superSz.height, PREF_H);
        return new Dimension(prefW, prefH);
    }

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

        JFrame frame = new JFrame("Foo Panel");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

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