JScrollPane问题

Question

我已经制作了一个带有滚动窗格的程序，但它不工作。请看源码：

JInfoView.java

package view;
import javax.swing.*;
import java.util.*;
import java.awt.*;
public class JInfoView extends JPanel {
    private JButton button = new JButton("ADD");
    private JButton buttonDelete = new JButton("DEL");
    private JTextField input = new JTextField("Text", 5);
    private JLabel label = new JLabel("Test");
    public JInfoView() {
        this.setLayout(new FlowLayout());
        this.add(button);
        this.add(buttonDelete);
        this.add(input);
        this.add(label);
    }
}

JMainView.java

package view;
import java.awt.*;
import javax.swing.*;
import java.util.*;
import view.JInfoView;

public class JMainView extends JFrame {
    private JPanel mypanel = new JPanel(new GridLayout(0, 1, 30, 50));
    private JScrollPane scrollPane = new JScrollPane(mypanel);
    public JMainView() {
        super("Simple Example");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Container container = this.getContentPane();
        container.setLayout(new FlowLayout());
        container.add(scrollPane);

        scrollPane.setVisible(true);
        scrollPane.setAutoscrolls(true); 

        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());       
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView()); 
        mypanel.add(new JInfoView());
    }

    public static void main(String[] args) {
        JMainView app = new JMainView();
        app.setVisible(true);
    }
}

我读过一篇教程，上面写道：

//In a container that uses a BorderLayout:
textArea = new JTextArea(5, 30);
...
JScrollPane scrollPane = new JScrollPane(textArea);
...
setPreferredSize(new Dimension(450, 110));
...
add(scrollPane, BorderLayout.CENTER);

我也做过同样的步骤，

private JPanel mypanel = new JPanel(new GridLayout(0, 1, 30, 50));
private JScrollPane scrollPane = new JScrollPane(mypanel);

然后添加了scrollpane：

container.add(scrollPane);

哪里出错了？编辑:问题是滚动窗格不工作。我给mypanel添加了很多JInfoView，但是滚动不起作用..

Answer 1

您忘记了像这样添加scrollPane.setPreferredSize调用：

public class JMainView extends JFrame {
    private JPanel mypanel = new JPanel(new GridLayout(0, 1, 30, 50));
    private JScrollPane scrollPane = new JScrollPane(mypanel);
    public JMainView() {
        super("Simple Example");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Container container = this.getContentPane();
        container.setLayout(new FlowLayout());
        container.add(scrollPane);

        scrollPane.setVisible(true);
        scrollPane.setAutoscrolls(true);
        scrollPane.setPreferredSize(new Dimension(300, 400)); //========== this was missed

        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        this.pack();
    }

    public static void main(String[] args) {
        JMainView app = new JMainView();
        app.setVisible(true);
    }
}

Answer 2

如果JScrollPane在BorderLayout的CENTER中，它似乎可以正常工作。例如。

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

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

public class JMainView extends JFrame {
    private JPanel mypanel = new JPanel(new GridLayout(0, 1, 30, 50));
    private JScrollPane scrollPane = new JScrollPane(mypanel);
    public JMainView() {
        super("Simple Example");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Container container = this.getContentPane();
        container.setLayout(new BorderLayout());
        container.add(scrollPane);

        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
        mypanel.add(new JInfoView());
    }

    public static void main(String[] args) {
        JMainView app = new JMainView();
        // important!
        app.pack();
        // show the scroll bars by compressing the GUI height
        app.setSize(
            (int)app.getSize().getWidth()+30, 
            (int)app.getSize().getHeight()/2);
        app.setVisible(true);
    }
}

class JInfoView extends JPanel {
    private JButton button = new JButton("ADD");
    private JButton buttonDelete = new JButton("DEL");
    private JTextField input = new JTextField("Text", 5);
    private JLabel label = new JLabel("Test");
    public JInfoView() {
        this.setLayout(new FlowLayout());
        this.add(button);
        this.add(buttonDelete);
        this.add(input);
        this.add(label);
    }
}