java-JScrollPane和JViewport的最大大小小于内容的滚动限制

2019-11-21 09:01:59 阅读：294 来源： 互联网

标签：swing jpanel jscrollpane jviewport java

我有一个JFrame,其中包含一个包含JPanel的JScrollPane.
JPanel包含一堆JTextAreas.
我正在其中加载很多文本(大约8k-10k个字符).

尽管滚动有点滞后,但布局工作正常.

真正的问题是,JPanel,JScrollPane和JViewport似乎有一个严格的32767大小限制,因此当任何JTextArea变得更高时,就无法进一步滚动以显示文本的最后1/3.

在下面,您可以看到该问题的最小示例.我使用了NetBeans JFrame设计器,因此它可能有点冗长,但是我从默认设置更改的唯一一件事是JTextAreas是JPanel的直接子代,滚动条策略和稍大的字体：

public class NewJFrame extends javax.swing.JFrame {

/**
 * Creates new form NewJFrame
 */
public NewJFrame() {
    initComponents();
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jScrollPane1 = new javax.swing.JScrollPane();
    jPanel1 = new javax.swing.JPanel();
    jTextArea1 = new javax.swing.JTextArea();
    jTextArea2 = new javax.swing.JTextArea();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    jScrollPane1.setHorizontalScrollBarPolicy(javax.swing.ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
    jScrollPane1.setVerticalScrollBarPolicy(javax.swing.ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

    jTextArea1.setColumns(20);
    jTextArea1.setFont(new java.awt.Font("Monospaced", 0, 14)); // NOI18N
    jTextArea1.setRows(5);

    jTextArea2.setColumns(20);
    jTextArea2.setFont(new java.awt.Font("Monospaced", 0, 14)); // NOI18N
    jTextArea2.setRows(5);
    jTextArea2.setText("Some long text...");

    javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
    jPanel1.setLayout(jPanel1Layout);
    jPanel1Layout.setHorizontalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addComponent(jTextArea1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jTextArea2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(0, 0, 0))
    );
    jPanel1Layout.setVerticalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(jTextArea1, javax.swing.GroupLayout.DEFAULT_SIZE, 342, Short.MAX_VALUE)
                .addComponent(jTextArea2))
            .addGap(0, 0, 0))
    );

    jScrollPane1.setViewportView(jPanel1);

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(jScrollPane1)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 96, Short.MAX_VALUE)
    );

    pack();
}// </editor-fold>                        

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    final NewJFrame f = new NewJFrame();
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for(javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels())
            if("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
    }catch(ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }catch(InstantiationException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }catch(IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }catch(javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            f.setVisible(true);
        }
    });
    StringBuilder txt = new StringBuilder();
    for(int i=0; i<10000; i++)
        txt.append(i).append("\n");
    f.jTextArea1.setText(txt.toString());
    txt = new StringBuilder();
    txt.append("JTextArea height: ").append(f.jTextArea1.getHeight()).append('\n');
    txt.append("JTextArea rows: ").append(f.jTextArea1.getRows()).append('\n');
    txt.append("JScrollPane height:").append(f.jScrollPane1.getHeight()).append('\n');
    txt.append("JViewport height:").append(f.jScrollPane1.getViewport().getHeight()).append('\n');
    txt.append("JPanel height:").append(f.jPanel1.getHeight()).append('\n');
    f.jTextArea2.setText(txt.toString());
}
// Variables declaration - do not modify                     
private javax.swing.JPanel jPanel1;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JTextArea jTextArea1;
private javax.swing.JTextArea jTextArea2;
// End of variables declaration                   
}

如果运行此命令并滚动到底部,您会希望看到计数达到10,000,但仅达到1637,并且您几乎可以看到下一行的顶部像素.

我已经尝试在JPanel,JScrollPane及其JViewport上设置setMaximumSize和setSize,但是没有任何改变.我也有些困惑,即使有一万行文本,其中一些可以滚动到足以查看的程度,但getRows()和getSize()方法仍返回原始值.

当我想使可滚动的JTextArea大于32767时,解决这种情况的正确方法是什么？

解决方法:

您的示例未正确同步,因为它更新了initial thread上的jTextArea2.请注意,JTextArea#setText()不再是线程安全的.下面的示例按照建议的here调用EditorKit#read()来加载相同的27 MB,176 K行文件(检查here).这需要几秒钟的时间,大约是JTable方法的两倍,但是滚动是可比较的.

import java.awt.EventQueue;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

/**
 * @see https://stackoverflow.com/a/25691384/230513
 */
public class Test {

    private static final String NAME = "/var/log/install.log";

    private void display() {
        JFrame f = new JFrame("Test");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JTextArea text = new JTextArea(24, 32);
        try {
            text.read(new BufferedReader(new FileReader(NAME)), null);
        } catch (IOException ex) {
            ex.printStackTrace(System.err);
        }
        f.add(new JScrollPane(text));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            new Test().display();
        });
    }
}

标签：swing,jpanel,jscrollpane,jviewport,java
来源： https://codeday.me/bug/20191121/2050748.html

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java-JScrollPane和JViewport的最大大小小于内容的滚动限制