添加填充有文本的 JTextArea/JTextPane 时防止 JSscrollPane 调整大小

Question

Hello people on the internet

My problem is that when I call setViewPortView(textArea) on the JScrollPane with the JTextArea already having text in it, the JScrollPane resizes to fit the entire text of the JTextArea . I would rather want the scroll pane to remain the same size while having the rest of the text hidden in the scroll pane below, so that I can scroll down to see the rest of the text.

See the below example that should be ready to run:

1. Click on the "Edit" button. The JTextPane is now replaced with a JTextArea which is editable.
2. Type into the JTextArea above the button. Type enough text so that it starts to scroll down as it's supposed to, many lines of text.
3. Click the same button again which is now titled "Save". Now a non editable JTextPane will be displayed in the JScrollPane instead of the JTextArea .
4. See how the JSCrollPane resized?

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Main extends JFrame {
    private final JScrollPane scrollPane;
    private final JTextArea textArea;
    private final JTextPane textPane;
    private final JButton editButton;
    private String text;

    private boolean isEditing = false;


    public Main() {
        setLayout(new GridBagLayout());
        textArea = new JTextArea();
        textArea.setVisible(false);
        textPane = new JTextPane();
        textPane.setEditable(false);
        scrollPane = new JScrollPane();
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setViewportView(textPane);
        editButton = new JButton("Edit");
        editButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                isEditing = !isEditing;
                textPane.setVisible(!isEditing);
                textArea.setVisible(isEditing);
                if(isEditing) {
                    scrollPane.setViewportView(textArea);
                    editButton.setText("Save");
                }
                else {
                    scrollPane.setViewportView(textPane);
                    editButton.setText("Edit");
                    text = textArea.getText();
                }
                textPane.setText(text);
            }
        });

        GridBagConstraints bag = new GridBagConstraints();
        bag.gridx = 0;
        bag.gridy = 0;
        bag.gridwidth = 3;
        bag.gridheight = 1;
        bag.weightx = 1.0;
        bag.weighty = 1.0;
        bag.fill = GridBagConstraints.BOTH;
        bag.anchor = GridBagConstraints.NORTH;
        bag.insets = new Insets(5, 5, 0, 5);
        add(scrollPane, bag);

        bag = new GridBagConstraints();
        bag.gridx = 1;
        bag.gridy = 1;
        bag.gridwidth = 1;
        bag.gridheight = 1;
        bag.weightx = 1.0;
        bag.weighty = 1.0;
        add(editButton, bag);

        setSize(1000, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            Main ui = new Main();
        });
    }
}

PS: I am swapping to a JTextPane because I am planning to render markdown text which I have excluded to keep the example simple. I am using JDK 8u231

I have tried saving the original size and setting it using setPreferredSize and setMaximumSize when I swap them out but it did not solve my problem. I would also like to keep it resizable for when the window resizes.

Update: I need to use the GridBag layout because I have a JPanel on which I draw by overriding the paint() function just above it

Answer 1

Swing components should determine their own preferred size. You should NOT be hardcoding random sizes. Then the layout manager can use this information.

The easiest way to do this is to give a hint to the JTextArea for the number of rows/columns it should contain by using:

JTextArea textArea = new JTextArea(15, 40);

You then use the appropriate layout manager to allow the components to dynamically resize as the frame size changes. I would use the BorderLayout for this. Then after you add the components to the frame you pack the frame.

A basic solution might be:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Main5 extends JFrame {
    private final JScrollPane scrollPane;
    private final JTextArea textArea;
    private final JTextPane textPane;
    private final JButton editButton;
    private String text;

    private boolean isEditing = false;


    public Main5() {
//        setLayout(new GridBagLayout());
//        textArea = new JTextArea();
//       textArea.setVisible(false);
        setLayout( new BorderLayout() );
        textArea = new JTextArea(15, 40);
        textPane = new JTextPane();
        textPane.setPreferredSize( textArea.getPreferredSize() );
        textPane.setEditable(false);
        scrollPane = new JScrollPane();
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setViewportView(textPane);

        editButton = new JButton("Edit");
        editButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                isEditing = !isEditing;
                textPane.setVisible(!isEditing);
//                textArea.setVisible(isEditing);
                if(isEditing) {
                    scrollPane.setViewportView(textArea);
                    editButton.setText("Save");
                    textArea.requestFocusInWindow();
                }
                else {
                    scrollPane.setViewportView(textPane);
                    editButton.setText("Edit");
                    text = textArea.getText();
                }
                textPane.setText(text);
            }
        });
/*
        GridBagConstraints bag = new GridBagConstraints();
        bag.gridx = 0;
        bag.gridy = 0;
        bag.gridwidth = 3;
        bag.gridheight = 1;
        bag.weightx = 1.0;
        bag.weighty = 1.0;
        bag.fill = GridBagConstraints.BOTH;
        bag.anchor = GridBagConstraints.NORTH;
        bag.insets = new Insets(5, 5, 0, 5);
        add(scrollPane, bag);

        bag = new GridBagConstraints();
        bag.gridx = 1;
        bag.gridy = 1;
        bag.gridwidth = 1;
        bag.gridheight = 1;
        bag.weightx = 1.0;
        bag.weighty = 1.0;
        add(editButton, bag);
*/
        add(scrollPane, BorderLayout.CENTER);

        JPanel wrapper = new JPanel();
        wrapper.add(editButton);
        add(wrapper, BorderLayout.PAGE_END);

//        setSize(1000, 500);
        pack();
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            Main5 ui = new Main5();
        });
    }
}

Even if you convert this to use a CardLayout it will still work because the size of the card panel is determined by the size of the largest panel added to it.

Answer 2

Ok I have found a solution. If I set the preferred size of the JScrollPane to some fixed value that is not too large then it still remains the size I want it to be and it doesn't grow vertically. It also resizes with the window when I resize the window. See the code below and thank you to Andrew Thompson in the comments for suggesting a CardLayout .

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Main extends JFrame {
    private final JScrollPane scrollPane;
    private final JTextArea textArea;
    private final JTextPane textPane;
    private final JButton editButton;
    private String text;
    private final JPanel cardPanel;
    private final CardLayout cards;

    private boolean isEditing = false;
    
    public Main() {
        setLayout(new GridBagLayout());
        textArea = new JTextArea();
        textPane = new JTextPane();
        textPane.setEditable(false);
        cards = new CardLayout();
        cardPanel = new JPanel();
        cardPanel.setLayout(cards);
        cardPanel.add(textPane);
        cardPanel.add(textArea);
        scrollPane = new JScrollPane(cardPanel);
        scrollPane.setPreferredSize(new Dimension(Integer.MAX_VALUE, 50));
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        editButton = new JButton("Edit");
        editButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                isEditing = !isEditing;
                if(isEditing) {
                    editButton.setText("Save");
                }
                else {
                    editButton.setText("Edit");
                    text = textArea.getText();
                }
                textPane.setText(text);
                cards.next(cardPanel);
            }
        });

        GridBagConstraints bag = new GridBagConstraints();
        bag.gridx = 0;
        bag.gridy = 0;
        bag.gridwidth = 3;
        bag.gridheight = 1;
        bag.weightx = 1.0;
        bag.weighty = 1.0;
        bag.fill = GridBagConstraints.BOTH;
        bag.anchor = GridBagConstraints.NORTH;
        bag.insets = new Insets(5, 5, 0, 5);
        add(scrollPane, bag);

        bag = new GridBagConstraints();
        bag.gridx = 1;
        bag.gridy = 1;
        bag.gridwidth = 1;
        bag.gridheight = 1;
        bag.weightx = 1.0;
        bag.weighty = 1.0;
        add(editButton, bag);

        setSize(1000, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            Main ui = new Main();
        });
    }
}

I have added: scrollPane.setPreferredSize(new Dimension(Integer.MAX_VALUE, 50));

I don't actually want it to be 50 but fortunately it doesn't make it 50 pixels high. I just wanted it to stay more or less half the height of the window as it was in the beginning.