dialog empty with JScrollPane und JPanel-CodePudding

i am trying to add the content to the mainPanel and mainpanel to the mainScrollPane. However, an empty dialog is displayed.

IMPORTANT: it must be implemented with JPanel and JScrollPane...

   `setModal(true);
    setTitle("Edit item");
    setDefaultCloseOperation(DISPOSE_ON_CLOSE);

    JPanel mainPanel = new JPanel();
    mainPanel.setPreferredSize(new Dimension(400, 700));

    JScrollPane mainScrollPane = new JScrollPane();
    mainScrollPane.add(mainPanel);
    setLayout(new BorderLayout());
    add(mainScrollPane);

    mainPanel.add(new JLabel("ID: "));
    mainPanel.add(txtID = new JTextField(item.getID()));
    mainPanel.add(new JLabel("Description: "));
    mainPanel.add(txtDescription = new JTextField(item.getDescription()));


    pack();
    setVisible(true);`

thank you, guys

CodePudding user response：

IMPORTANT: it must be implemented with JPanel and JScrollPane...

JScrollPane mainScrollPane = new JScrollPane();
mainScrollPane.add(mainPanel);

You should NOT be adding component directly to the scroll pane. Instead you need to add the component to the viewport of the scroll pane.

This can be done by using:

JScrollPane mainScrollPane = new JScrollPane(mainPaneol);
//mainScrollPane.add(mainPanel);

JScrollPane mainScrollPane = new JScrollPane();
//mainScrollPane.add(mainPanel);
mainScrollPane.setViewportView(mainPanel);

The scroll pane is then added to the frame as your code currently does.

Note you won't notice the usage of the scroll pane because there is currently no reason for the scroll bars to appear. So there really is no need to use a scroll pane, you can just add the panel directly to the frame.

CodePudding user response：

Please provide a minimal reproducible example. It could look like what follows:

MyFrame.java

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

class Item { 
    String id; 
    String description; 
    Item(String id, String description) {this.id = id;this.description = description;}
    String getId() {return id;}
    String getDescription() {return description;}
}

public class MyFrame extends JFrame {
    Item item = new Item("007", "Special watch");
    public MyFrame() {
        // setModal(true);
        setTitle("Edit item");
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);

        JPanel mainPanel = new JPanel();
        mainPanel.setPreferredSize(new Dimension(400, 700));

        mainPanel.add(new JLabel("ID: "));
        mainPanel.add(new JTextField(item.getId()));
        mainPanel.add(new JLabel("Description: "));
        mainPanel.add(new JTextField(item.getDescription()));

        /* From Oracle's documentation, see link below: 
           Creates a JScrollPane that displays the contents of the
           specified component, where both horizontal and vertical
           scrollbars appear whenever the component's contents are
           larger than the view.
        */
        JScrollPane mainScrollPane = new JScrollPane(mainPanel);

        // Just to show the bars
        mainScrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);  
        mainScrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);  

        getContentPane().add(mainScrollPane); // <- This makes it shine!

        pack();
        setVisible(true);
    }

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

$ javac MyFrame.java
$ java MyFrame

Et voilà:

https://docs.oracle.com/javase/8/docs/api/javax/swing/JScrollPane.html