Question

我正在尝试构建一个动态日志窗口（基本上是一个自动滚动的jtext-area）。

我遇到的问题是，虽然我在文本区域打印了500行，但显示如下：

enter image description here

下面是我的代码：

    import java.awt.Dimension;

import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.text.DefaultCaret;


public class Main {

    private static JFrame mainFrame;

    public static void main(String args[]) {
        mainFrame = new JFrame();
        mainFrame.setSize(500, 500);

        mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        ControlPanel cp = new ControlPanel();
        mainFrame.add(cp);
        mainFrame.setVisible(true);
    }
}

class ControlPanel extends JPanel {

private JButton resetButton = new JButton("Reset");

private JPanel logPanel = new JPanel();

private JLabel actionLogsLabel = new JLabel("Action Log");

private JLabel pointsLogsLabel = new JLabel("Points Log");

private JTextArea actionLog = new JTextArea();

private JTextArea pointsLog = new JTextArea();

private JScrollPane actionScroll;

private JScrollPane pointsScroll;

public ControlPanel() {
    init();

    this.add(resetButton);
    this.add(logPanel);
}

private void init() {
    this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
    this.setAlignmentX(LEFT_ALIGNMENT);
    this.logPanel.setLayout(new BoxLayout(logPanel, BoxLayout.Y_AXIS));
    this.logPanel.setAlignmentX(LEFT_ALIGNMENT);

    actionLog.setPreferredSize(new Dimension(500, 300));
    actionLog.setMaximumSize(actionLog.getPreferredSize());
    actionLog.setEditable(false);
    actionLog.setWrapStyleWord(true);
    DefaultCaret caret = (DefaultCaret) actionLog.getCaret();
    caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

    pointsLog.setPreferredSize(new Dimension(500, 300));
    pointsLog.setMaximumSize(pointsLog.getPreferredSize());
    pointsLog.setEditable(false);
    pointsLog.setWrapStyleWord(true);

    pointsScroll = new JScrollPane(pointsLog, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
    actionScroll = new JScrollPane(actionLog, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);

    logPanel.add(actionLogsLabel);
    logPanel.add(actionScroll);

    for(int i = 0; i < 500; i++) {
        actionLog.setText(actionLog.getText() + "Line: " + i + "\n");
    }

    logPanel.add(pointsLogsLabel);
    logPanel.add(pointsScroll);
}
}

希望有更多Swing经验的人可以花点时间用正确的方式指出我。

Answer 1

永远不要这样做：

actionLog.setPreferredSize(new Dimension(500, 300));

因为这样做会人为地限制JTextArea的大小，从而导致当前令您烦恼的效果。另请注意，避免在任何设置上设置首选尺寸通常是个好主意。

而是设置JTextARea的列数和行数。这可以通过setter方法或通过简单的构造函数调用来完成：JTextArea myTextArea = new JTextArea(rows, columns);

顺便说一句：我想知道JList是否会更适合您。

MCVE示例：

import javax.swing.*;
import javax.swing.text.DefaultCaret;

public class Main2 {

   private static void createAndShowGUI() {
      JPanel mainPanel = new ControlPanel();

      JFrame frame = new JFrame("Main2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGUI();
         }
      });
   }
}

class ControlPanel extends JPanel {
   private static final int LOG_ROWS = 15;
   private static final int LOG_COLS = 40;
   private JButton resetButton = new JButton("Reset");
   private JPanel logPanel = new JPanel();
   private JLabel actionLogsLabel = new JLabel("Action Log");
   private JLabel pointsLogsLabel = new JLabel("Points Log");
   private JTextArea actionLog = new JTextArea();
   private JTextArea pointsLog = new JTextArea();
   private JScrollPane actionScroll;
   private JScrollPane pointsScroll;

   public ControlPanel() {
      init();
      this.add(resetButton);
      this.add(logPanel);
   }

   private void init() {
      this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
      this.setAlignmentX(LEFT_ALIGNMENT);
      this.logPanel.setLayout(new BoxLayout(logPanel, BoxLayout.Y_AXIS));
      this.logPanel.setAlignmentX(LEFT_ALIGNMENT);
      // !! actionLog.setPreferredSize(new Dimension(500, 300));
      // !! actionLog.setMaximumSize(actionLog.getPreferredSize());
      actionLog.setRows(LOG_ROWS); // !!
      actionLog.setColumns(LOG_COLS); // !!

      actionLog.setEditable(false);
      actionLog.setWrapStyleWord(true);
      DefaultCaret caret = (DefaultCaret) actionLog.getCaret();
      caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
      // !! pointsLog.setPreferredSize(new Dimension(500, 300));
      // !! pointsLog.setMaximumSize(pointsLog.getPreferredSize());
      pointsLog.setRows(LOG_ROWS); // !!
      pointsLog.setColumns(LOG_COLS); // !!

      pointsLog.setEditable(false);
      pointsLog.setWrapStyleWord(true);
      pointsScroll = new JScrollPane(pointsLog,
            JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
            JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
      actionScroll = new JScrollPane(actionLog,
            JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
            JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
      logPanel.add(actionLogsLabel);
      logPanel.add(actionScroll);
      for (int i = 0; i < 500; i++) {
         actionLog.setText(actionLog.getText() + "Line: " + i + "\n");
      }
      logPanel.add(pointsLogsLabel);
      logPanel.add(pointsScroll);
   }
}

修改
嵌套布局和JLists的示例：

import java.awt.GridBagConstraints; import java.awt.GridBagLayout; import javax.swing.*; public class Main2B { private static void createAndShowGUI() { ControlPanel2B controlPanel = new ControlPanel2B(); controlPanel.setBorder(BorderFactory.createEtchedBorder()); JPanel mainPanel = new JPanel(new GridBagLayout()); GridBagConstraints gbc = new GridBagConstraints(); mainPanel.add(controlPanel, gbc); JFrame frame = new JFrame("Main2"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().add(mainPanel); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } } @SuppressWarnings("serial") class ControlPanel2B extends JPanel { private static final int LOG_ROWS = 15; private static final int LIST_WIDTH = 500; private JButton resetButton = new JButton("Reset"); private JPanel logPanel = new JPanel(); private JLabel actionLogsLabel = new JLabel("Action Log"); private JLabel pointsLogsLabel = new JLabel("Points Log"); private DefaultListModel<String> actionLogListModel = new DefaultListModel<>(); private JList<String> actionLogList = new JList<String>(actionLogListModel); private DefaultListModel<String> pointsLogListModel = new DefaultListModel<>(); private JList<String> pointsLogList = new JList<String>(pointsLogListModel); private JScrollPane actionScroll; private JScrollPane pointsScroll; public ControlPanel2B() { init(); this.add(resetButton); this.add(logPanel); } private void init() { actionLogList.setVisibleRowCount(LOG_ROWS); pointsLogList.setVisibleRowCount(LOG_ROWS); actionLogList.setFixedCellWidth(LIST_WIDTH); this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS)); this.setAlignmentX(LEFT_ALIGNMENT); this.logPanel.setLayout(new BoxLayout(logPanel, BoxLayout.Y_AXIS)); this.logPanel.setAlignmentX(LEFT_ALIGNMENT); pointsScroll = new JScrollPane(pointsLogList, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER); actionScroll = new JScrollPane(actionLogList, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER); logPanel.add(actionLogsLabel); logPanel.add(actionScroll); for (int i = 0; i < 500; i++) { actionLogListModel.addElement("Line: " + i); } logPanel.add(pointsLogsLabel); logPanel.add(pointsScroll); } }

使用ScrollPane自动滚动JTextArea？

1 个答案: