如何在Java中使JTextArea占据GridBagLayout中最大宽度的80%

Question

我正在尝试创建一个聊天窗口，但我似乎不知道如何使JTextArea占据GridBagLayout中可用宽度空间的最大80%。换言之，如果文本似乎占据了窗口的整个宽度，那么它应该只能占据宽度的80%，只需换行即可。此外，如果文本小于80%，比如说40%，那么JTextArea应该只包装40%，而不是整个80%
我使用的是GridBagLayout，我已将GridBagConstraints weightx设置为1.0，并将填充设置为水平，左侧或右侧插入40，具体取决于用户。但我似乎不能让JTextArea来包装文本，如果需要，允许它使用窗口宽度的80%，否则就要包装文本。

下面是我编写的当前代码：

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.util.LinkedList;
import java.util.List;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.Scrollable;
import javax.swing.SwingUtilities;


public class ChatWindow {

    private JFrame mMainFrame;

    public ChatWindow(List<ChatEntry> chatContentList) {
        // Create JFrame, set window size and center on screen.
        mMainFrame = new JFrame();
        mMainFrame.setTitle("Chat Window");
        mMainFrame.setSize(360, 600);
        mMainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        mMainFrame.setLocationRelativeTo(null);

        // Create parent container JPanel for all other JComponents.
        JPanel mainPanel = new JPanel();
        mainPanel.setLayout(new GridBagLayout());

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.weightx = 1.0;
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        mainPanel.add(buildChatUI(chatContentList), gbc);

        // Add empty JPanel as an object to fill the empty space available.
        gbc.fill = GridBagConstraints.BOTH;
        gbc.weighty = 1.0;
        mainPanel.add(new JPanel(), gbc);

        mMainFrame.getContentPane().add(new JScrollPane(new VerticalScrollPane(mainPanel)));
        mMainFrame.setVisible(true);
    }

    public JPanel buildChatUI(List<ChatEntry> chatContentList) {
        JPanel chatPanel = new JPanel();
        chatPanel.setLayout(new GridBagLayout());
        chatPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

        GridBagConstraints gbc = new GridBagConstraints();

        for (ChatEntry chatEntry : chatContentList) {
            JLabel nameLabel = new JLabel(chatEntry.name);

            JTextArea contentTextArea = new JTextArea();
            contentTextArea.setText(chatEntry.content);
            contentTextArea.setOpaque(true);
            contentTextArea.setLineWrap(true);
            contentTextArea.setWrapStyleWord(true);
            contentTextArea.setEditable(false);

            // Arrange each chat entry based on the user.
            if (chatEntry.type == 1) {
                contentTextArea.setBackground(Color.YELLOW);
                gbc.anchor = GridBagConstraints.WEST;
            }
            else {
                contentTextArea.setBackground(Color.CYAN);
                gbc.anchor = GridBagConstraints.EAST;
            }

            gbc.insets.set(0, 0, 0, 0);
            gbc.weightx = 1.0;
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.fill = GridBagConstraints.NONE;
            chatPanel.add(nameLabel, gbc);

            if (gbc.anchor == GridBagConstraints.WEST) {
                gbc.fill = GridBagConstraints.HORIZONTAL;
                gbc.insets.set(0, 0, 0, 40);
                chatPanel.add(contentTextArea, gbc);
            }
            else {
                gbc.fill = GridBagConstraints.HORIZONTAL;
                gbc.insets.set(0, 40, 0, 0);
                chatPanel.add(contentTextArea, gbc);
            }
        }

        return chatPanel;
    }


    /**
     * This class is used to make the JTextArea lines wrap every time the window
     * is resized. Without this, the JTextArea lines will not shrink back if the
     * parent window shrinks. This is achieved by returning true on getScrollableTracksViewportWidth();
     */
    private class VerticalScrollPane extends JPanel implements Scrollable {

        private static final long serialVersionUID = 7477168367035025136L;

        public VerticalScrollPane() {
            this(new GridLayout(0, 1));
        }

        public VerticalScrollPane(LayoutManager lm) {
            super(lm);
        }

        public VerticalScrollPane(Component comp) {
            this();
            add(comp);
        }

        @Override
        public Dimension getPreferredScrollableViewportSize() {
            return getPreferredSize();
        }

        @Override
        public int getScrollableUnitIncrement(Rectangle visibleRect,
                int orientation, int direction) {
            return 10;
        }

        @Override
        public int getScrollableBlockIncrement(Rectangle visibleRect,
                int orientation, int direction) {
            return 100;
        }

        @Override
        public boolean getScrollableTracksViewportWidth() {
            return true;
        }

        @Override
        public boolean getScrollableTracksViewportHeight() {
            return false;
        }

    }

    /**
     * Class structure for storing a single chat entry in a full conversation.
     */
    public static class ChatEntry {
        public String name;
        public String content;

        // For type 0=sent, 1=received.
        public int type;

        public ChatEntry(String name, String content, int type) {
            this.name = name;
            this.content = content;
            this.type = type;
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                // Simulate a conversation between two users and pass it on to the
                // chat window to test the UI.
                List<ChatEntry> chatContentList = new LinkedList<>();
                chatContentList.add(new ChatEntry("David", "Hey Lori, how are you?", 0));
                chatContentList.add(new ChatEntry("Lori", "Hi David, I'm good. What have you been up to?", 1));
                chatContentList.add(new ChatEntry("David", "I've been super busy with work.", 0));
                chatContentList.add(new ChatEntry("David", "Haven't had much free time to even go out to eat.", 0));
                chatContentList.add(new ChatEntry("Lori", "I know what you mean, I've had to work on projects after projects.", 1));
                chatContentList.add(new ChatEntry("David", "Let's make some time and go to lunch tomorrow!", 0));
                chatContentList.add(new ChatEntry("Lori", "That sounds great, let's do 12pm. I know a great food truck by my building.", 1));
                chatContentList.add(new ChatEntry("David", "Perfect, I'll meet you at the entrance of your building.", 0));
                chatContentList.add(new ChatEntry("Lori", "Awesome, see you tomorrow :)", 1));
                new ChatWindow(chatContentList);
            }
        });
    }

}

Answer 1

代码如下：

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.font.FontRenderContext;
import java.awt.font.LineBreakMeasurer;
import java.awt.geom.Area;
import java.awt.geom.RoundRectangle2D;
import java.text.AttributedCharacterIterator;
import java.text.AttributedString;
import java.util.LinkedList;
import java.util.List;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.Scrollable;
import javax.swing.SwingUtilities;


public class ChatWindow {

    private JFrame mMainFrame;

    public ChatWindow(List<ChatEntry> chatContentList) {
        // Create JFrame, set window size and center on screen.
        mMainFrame = new JFrame();
        mMainFrame.setTitle("Chat Window");
        mMainFrame.setSize(360, 600);
        mMainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        mMainFrame.setLocationRelativeTo(null);

        // Create parent container JPanel for all other JComponents.
        JPanel mainPanel = new JPanel();
        mainPanel.setLayout(new GridBagLayout());

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.weightx = 1.0;
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        mainPanel.add(buildChatUI(chatContentList), gbc);

        // Add empty JPanel as an object to fill the empty space available.
        gbc.fill = GridBagConstraints.BOTH;
        gbc.weighty = 1.0;
        mainPanel.add(new JPanel(), gbc);

        mMainFrame.getContentPane().add(new JScrollPane(new VerticalScrollPane(mainPanel)));
        mMainFrame.setVisible(true);
    }

    public JPanel buildChatUI(List<ChatEntry> chatContentList) {
        JPanel chatPanel = new JPanel();
        chatPanel.setLayout(new GridBagLayout());
        chatPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

        GridBagConstraints gbc = new GridBagConstraints();

        for (ChatEntry chatEntry : chatContentList) {
            JLabel nameLabel = new JLabel(chatEntry.name);

            BubblePane bubble = new BubblePane(chatPanel, chatEntry.content);

            // Arrange each chat entry based on the user.
            if (chatEntry.type == 1) {
                bubble.setBackground(Color.YELLOW);
                gbc.anchor = GridBagConstraints.WEST;
            }
            else {
                bubble.setBackground(Color.CYAN);
                gbc.anchor = GridBagConstraints.EAST;
            }

            gbc.insets.set(0, 0, 0, 0);
            gbc.weightx = 1.0;
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.fill = GridBagConstraints.NONE;
            chatPanel.add(nameLabel, gbc);

            if (gbc.anchor == GridBagConstraints.WEST) {
                gbc.fill = GridBagConstraints.HORIZONTAL;
                gbc.insets.set(0, 0, 10, 40);
                chatPanel.add(bubble, gbc);
            }
            else {
                gbc.fill = GridBagConstraints.HORIZONTAL;
                gbc.insets.set(0, 40, 10, 0);
                chatPanel.add(bubble, gbc);
            }
        }

        return chatPanel;
    }

    private class BubblePane extends JTextArea {

        private static final long serialVersionUID = -6113801969569504295L;

        private int radius = 10;
        private int strokeThickness = 3;
        private int padding = strokeThickness / 2;
        private JPanel mParent;

        public BubblePane(JPanel parent, String text) {
            mParent = parent;

            setOpaque(false);
            setLineWrap(true);
            setWrapStyleWord(true);
            setEditable(false);
            setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
            setText(text);
        }

        @Override
        public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D) g;
            g2d.setColor(getBackground());
            int x = padding + strokeThickness;
            int width = getWidth() - (strokeThickness * 2);
            int bottomLineY = getHeight() - strokeThickness;
            g2d.fillRect(x, padding, width, bottomLineY);
            g2d.setRenderingHints(new RenderingHints(
                    RenderingHints.KEY_ANTIALIASING,
                    RenderingHints.VALUE_ANTIALIAS_ON));
            g2d.setStroke(new BasicStroke(strokeThickness));
            RoundRectangle2D.Double rect = new RoundRectangle2D.Double(x, padding,
                    width, bottomLineY, radius, radius);
            Area area = new Area(rect);
            g2d.draw(area);


            int lc = countLines(this);
            GridBagLayout gbl = (GridBagLayout) mParent.getLayout();
            GridBagConstraints constraints = gbl.getConstraints(this);
            if (lc == 1) {
                if (constraints.fill == GridBagConstraints.HORIZONTAL) {
                    constraints.fill = GridBagConstraints.NONE;
                    gbl.setConstraints(this, constraints);
                    this.setSize(
                            getFontMetrics(getFont()).stringWidth(getText()) + 
                            this.getBorder().getBorderInsets(this).left +
                            this.getBorder().getBorderInsets(this).right, 
                            getHeight() +
                            this.getBorder().getBorderInsets(this).top + 
                            this.getBorder().getBorderInsets(this).bottom);
                }
            } else {
                if (constraints.fill == GridBagConstraints.NONE) {
                    constraints.fill = GridBagConstraints.HORIZONTAL;
                    gbl.setConstraints(this, constraints);

                }
            }

            super.paintComponent(g);
        }

        private int countLines(JTextArea textArea) {
            AttributedString text = new AttributedString(textArea.getText());
            FontRenderContext frc = textArea.getFontMetrics(textArea.getFont())
                    .getFontRenderContext();
            AttributedCharacterIterator charIt = text.getIterator();
            LineBreakMeasurer lineMeasurer = new LineBreakMeasurer(charIt, frc);
            float formatWidth = (float) textArea.getSize().width;
            lineMeasurer.setPosition(charIt.getBeginIndex());

            int noLines = 0;
            while (lineMeasurer.getPosition() < charIt.getEndIndex()) {
                lineMeasurer.nextLayout(formatWidth);
                noLines++;
            }

            return noLines;
        }
    }


    /**
     * This class is used to make the JTextArea lines wrap every time the window
     * is resized. Without this, the JTextArea lines will not shrink back if the
     * parent window shrinks. This is achieved by returning true on getScrollableTracksViewportWidth();
     */
    private class VerticalScrollPane extends JPanel implements Scrollable {

        private static final long serialVersionUID = 7477168367035025136L;

        public VerticalScrollPane() {
            this(new GridLayout(0, 1));
        }

        public VerticalScrollPane(LayoutManager lm) {
            super(lm);
        }

        public VerticalScrollPane(Component comp) {
            this();
            add(comp);
        }

        @Override
        public Dimension getPreferredScrollableViewportSize() {
            return getPreferredSize();
        }

        @Override
        public int getScrollableUnitIncrement(Rectangle visibleRect,
                int orientation, int direction) {
            return 10;
        }

        @Override
        public int getScrollableBlockIncrement(Rectangle visibleRect,
                int orientation, int direction) {
            return 100;
        }

        @Override
        public boolean getScrollableTracksViewportWidth() {
            return true;
        }

        @Override
        public boolean getScrollableTracksViewportHeight() {
            return false;
        }
    }

    /**
     * Class structure for storing a single chat entry in a full conversation.
     */
    public static class ChatEntry {
        public String name;
        public String content;

        // For type 0=sent, 1=received.
        public int type;

        public ChatEntry(String name, String content, int type) {
            this.name = name;
            this.content = content;
            this.type = type;
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                // Simulate a conversation between two users and pass it on to the
                // chat window to test the UI.
                List<ChatEntry> chatContentList = new LinkedList<>();
                chatContentList.add(new ChatEntry("David", "Hey Lori, how are you?", 0));
                chatContentList.add(new ChatEntry("Lori", "Hi David, I'm good. What have you been up to?", 1));
                chatContentList.add(new ChatEntry("David", "I've been super busy with work.", 0));
                chatContentList.add(new ChatEntry("David", "Haven't had much free time to even go out to eat.", 0));
                chatContentList.add(new ChatEntry("Lori", "I know what you mean, I've had to work on projects after projects.", 1));
                chatContentList.add(new ChatEntry("David", "Let's make some time and go to lunch tomorrow!", 0));
                chatContentList.add(new ChatEntry("Lori", "That sounds great, let's do 12pm. I know a great food truck by my building.", 1));
                chatContentList.add(new ChatEntry("David", "Perfect, I'll meet you at the entrance of your building.", 0));
                chatContentList.add(new ChatEntry("Lori", "Awesome, see you tomorrow :)", 1));
                new ChatWindow(chatContentList);
            }
        });
    }

}

Answer 2

调整窗口大小时，重新显示文本区域是一种耗时的方法。我已经为每个聊天条目添加了ComponentListeners，这将调整条目TextArea的大小。这只是概念的证明，可以在性能方面加以改进。

尝试以下操作并减小窗口宽度，然后慢慢加宽以查看效果。它类似于您想象的目标。当窗口打开时，我还没有设法立即实现该布局。虽然慢慢加宽窗口效果很好，但如果您移动得太快，那么由于JDK代码中的缓存，线条可能会显得太宽。

无论如何，我想我分享了我的实验，也许它可以帮助您找到处理它的方法。我假设您可能必须实现自己的布局管理器来完全实现您的既定目标并绕过观察到的缓存。

计算TextArea内行数的方法取自另一个StackOverflow问题：如何计算JTextArea中的行数，包括由包装引起的行数？

public JPanel buildChatUI(List<ChatEntry> chatContentList) {
    final JPanel chatPanel = new JPanel();
    chatPanel.setLayout(new GridBagLayout());
    chatPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

    GridBagConstraints gbc = new GridBagConstraints();

    for (ChatEntry chatEntry : chatContentList) {
        JLabel nameLabel = new JLabel(chatEntry.name);

        final JTextArea contentTextArea = new JTextArea();
        contentTextArea.setText(chatEntry.content);
        contentTextArea.setOpaque(true);
        contentTextArea.setLineWrap(true);
        contentTextArea.setWrapStyleWord(true);
        contentTextArea.setEditable(false);
        chatPanel.addComponentListener(new ComponentListener() {
            @Override
            public void componentResized(ComponentEvent e) {
                int lc = countLines(contentTextArea);
                GridBagLayout gbl = (GridBagLayout) chatPanel.getLayout();
                GridBagConstraints constraints = gbl.getConstraints(contentTextArea);
                if (lc == 1) {
                    if (constraints.fill == GridBagConstraints.HORIZONTAL) {
                        constraints.fill = GridBagConstraints.NONE;
                        gbl.setConstraints(contentTextArea, constraints);
                    }
                } else {
                    if (constraints.fill == GridBagConstraints.NONE) {
                        constraints.fill = GridBagConstraints.HORIZONTAL;
                        gbl.setConstraints(contentTextArea, constraints);
                    }
                }
            }
            @Override public void componentMoved(ComponentEvent e) { }
            @Override public void componentShown(ComponentEvent e) { }
            @Override public void componentHidden(ComponentEvent e) { }
        });

        // Arrange each chat entry based on the user.
        if (chatEntry.type == 1) {
            contentTextArea.setBackground(Color.YELLOW);
            gbc.anchor = GridBagConstraints.WEST;
        }
        else {
            contentTextArea.setBackground(Color.CYAN);
            gbc.anchor = GridBagConstraints.EAST;
        }

        gbc.insets.set(0, 0, 0, 0);
        gbc.weightx = 1.0;
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        gbc.fill = GridBagConstraints.NONE;
        chatPanel.add(nameLabel, gbc);
        gbc.fill = GridBagConstraints.HORIZONTAL;
        if (gbc.anchor == GridBagConstraints.WEST) {
            gbc.insets.set(0, 0, 0, 40);
            chatPanel.add(contentTextArea, gbc);
        }
        else {
            gbc.insets.set(0, 40, 0, 0);
            chatPanel.add(contentTextArea, gbc);
        }
    }

    return chatPanel;
}

/**
 * From https://stackoverflow.com/questions/6366776/how-to-count-the-number-of-lines-in-a-jtextarea-including-those-caused-by-wrapp
 * @param textArea the text area of interest
 * @return number of lines in text area
 */
private static int countLines(JTextArea textArea) {
    AttributedString text = new AttributedString(textArea.getText());
    FontRenderContext frc = textArea.getFontMetrics(textArea.getFont())
            .getFontRenderContext();
    AttributedCharacterIterator charIt = text.getIterator();
    LineBreakMeasurer lineMeasurer = new LineBreakMeasurer(charIt, frc);
    float formatWidth = (float) textArea.getSize().width;
    lineMeasurer.setPosition(charIt.getBeginIndex());

    int noLines = 0;
    while (lineMeasurer.getPosition() < charIt.getEndIndex()) {
        lineMeasurer.nextLayout(formatWidth);
        noLines++;
    }

    return noLines;
}