MigLayout resizing with JScrollPane

Question

I searched a little bit and did not find a good answer to my problem. I am working on a gui that has to be resizable. It contains a status `JTextArea` that is inside a `JScrollPane`. And this is my problem. As long as I don't manually resize my JFrame, the "initial" layout is kept and everything looks fine. As soon as I manually resize (if the `JTextArea` is already in scrolled mode), the layout gets messed up. Here is a SSCCE (I got rid of most of the parts while keeping the structure of the code. I hope it's more readable that way): ``` import java.awt.Color; import java.awt.Font; import javax.swing.BorderFactory; import javax.swing.JComboBox; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JSeparator; import javax.swing.JSlider; import javax.swing.JTabbedPane; import javax.swing.JTextArea; import javax.swing.JTextField; import javax.swing.border.TitledBorder; import net.miginfocom.swing.MigLayout; p…

Accepted Answer

Focusing on your status area and using nested layouts produces the result shown below. Note in particular,

- Use `invokeLater()` to construct the GUI on the EDT.

- Use `javax.swing.Timer` to update the GUI on the EDT.

- Use `pack()` to make the window fit the preferred size and layouts of its subcomponents.

- Use the update policy of `DefaultCaret` to control scrolling.

- Avoid needless lazy instantiation in public accessors.

- Avoid `setXxxSize()`; override `getXxxSize()` judiciously.

- Critically examine the decision to extend `JFrame`.

```
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSeparator;
import javax.swing.JTabbedPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.Timer;
import javax.swing.border.TitledBorder;
import javax.swing.text.DefaultCaret;

public class Tab extends JFrame {

private JTextArea messageTextArea;
    private JPanel optionPanel, messagePanel;
    private JTabbedPane plotTabPane;

public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

@Override
            public void run() {

final Tab tab = new Tab();
                tab.setVisible(true);
                Timer t = new Timer(200, new ActionListener() {

int count = 0;

@Override
                    public void actionPerformed(ActionEvent e) {
                        tab.printRawMessage("testMessage" + count++);
                    }
                });
                t.start();
            }
        });
    }

public Tab() {
        initComponents();
    }

private void initComponents() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel mainPanel = new JPanel(new GridLayout(1, 0));
        Box leftPanel = new Box(BoxLayout.Y_AXIS);
        leftPanel.add(getLeftTopPanel());
        leftPanel.add(getMessagePanel());
        mainPanel.add(leftPanel);
        mainPanel.add(getRightPanel());
        this.add(mainPanel);
        this.pack();
        this.setLocationRelativeTo(null);
    }

protected JPanel getLeftTopPanel() {
        optionPanel = new JPanel();
        optionPanel.setBorder(BorderFactory.createTitledBorder(null,
            "Configuration", TitledBorder.LEFT, TitledBorder.TOP,
            new Font("null", Font.BOLD, 12), Color.BLUE));
        JLabel label = new JLabel("Choose");
        label.setHorizontalAlignment(JLabel.RIGHT);
        optionPanel.add(label);
        optionPanel.add(new JSeparator(JSeparator.VERTICAL));
        optionPanel.add(new JComboBox(
            new String[]{"option1", "option2", "option3"}));
        optionPanel.add(new JLabel("Type"));
        optionPanel.add(new JTextField("3"));
        return optionPanel;
    }

protected JTabbedPane getRightPanel() {
        plotTabPane = new JTabbedPane();
        plotTabPane.add("Tab1", new JPanel());
        plotTabPane.add("Tab2", new JPanel());
        return plotTabPane;
    }

protected JPanel getMessagePanel() {
        messagePanel = new JPanel(new GridLayout());
        messagePanel.setBorder(BorderFactory.createTitledBorder(null,
            "Status Console", TitledBorder.LEFT, TitledBorder.TOP,
            new Font("null", Font.BOLD, 12), Color.BLUE));
        final JScrollPane sp = new JScrollPane(getMessageTextArea());
        sp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        messagePanel.add(sp);
        return messagePanel;
    }

protected JTextArea getMessageTextArea() {
        messageTextArea = new JTextArea("", 10, 19);
        messageTextArea.setEditable(false);
        messageTextArea.setFont(new Font(null, Font.PLAIN, 20));
        messageTextArea.setBorder(BorderFactory.createEmptyBorder(4, 4, 4, 4));
        DefaultCaret caret = (DefaultCaret) messageTextArea.getCaret();
        caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
        return messageTextArea;
    }

public void printRawMessage(String rawMessage) {
        messageTextArea.append(rawMessage + "
");
    }
}
```

MigLayout resizing with JScrollPane

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