如何将 JTextArea 添加到 JScrollPane？

Question

我正在尝试创建一个简单的文本编辑器，但在尝试使用 JTextArea 并通过 JScrollPane 使其可滚动时遇到了运行问题。

我所知道的常规方法都不起作用，所以我想知道这里是否有任何人可以提供帮助。我不确定从哪里开始，所以我要 post 我的整个代码。我对其进行了注释以帮助展示我的方法的作用。

import javax.swing.*;
import javax.swing.filechooser.FileNameExtensionFilter;
import javax.swing.text.*;

import java.awt.*;
import java.io.*;
import java.awt.event.*;
import java.util.Hashtable;

@SuppressWarnings("serial")
public class GrooveEditor extends JFrame {

  private Action openAction = new OpenAction();
  private Action saveAction = new SaveAction();

  private JTextComponent textComp;

  @SuppressWarnings({ "rawtypes", "unused" })
  private Hashtable actionHash = new Hashtable();

  public static void main(String[] args) {
    GrooveEditor editor = new GrooveEditor();
    editor.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    editor.setVisible(true);
  }

  // Create editor.
  public GrooveEditor() {

    super("Groove Text Editor");
    textComp = createTextComponent();
    makeActionsPretty();

    Container content = getContentPane();
    content.add(textComp, BorderLayout.CENTER);
    setJMenuBar(createMenuBar());
    setExtendedState(MAXIMIZED_BOTH); 
    }

  // Create JTextComponent subclass.
  private JTextComponent createTextComponent() {
    JTextArea ta = new JTextArea();
    ta.setLineWrap(true);
    ta.setMargin(new Insets(10,10,10,10));
    return ta;
  }

  protected void makeActionsPretty() {
    Action a;
    a = textComp.getActionMap().get(DefaultEditorKit.cutAction);
    a.putValue(Action.SMALL_ICON, new ImageIcon("icons/cut.gif"));
    a.putValue(Action.NAME, "Cut");

    a = textComp.getActionMap().get(DefaultEditorKit.copyAction);
    a.putValue(Action.SMALL_ICON, new ImageIcon("icons/copy.gif"));
    a.putValue(Action.NAME, "Copy");

    a = textComp.getActionMap().get(DefaultEditorKit.pasteAction);
    a.putValue(Action.SMALL_ICON, new ImageIcon("icons/paste.gif"));
    a.putValue(Action.NAME, "Paste");

    a = textComp.getActionMap().get(DefaultEditorKit.selectAllAction);
    a.putValue(Action.NAME, "Select All");
  }



  // Create a JMenuBar
  protected JMenuBar createMenuBar() {
    JMenuBar menubar = new JMenuBar();
    menubar.add( Box.createHorizontalStrut(10));
    JMenu file = new JMenu("File");
    JMenu edit = new JMenu("Edit");
    JMenu format = new JMenu("Format");

    menubar.add(file);
    menubar.add(edit);
    menubar.add(format);

    file.add(getOpenAction());
    file.add(getSaveAction());
    file.add(new ExitAction());

    edit.add(textComp.getActionMap().get(DefaultEditorKit.cutAction));
    edit.add(textComp.getActionMap().get(DefaultEditorKit.copyAction));
    edit.add(textComp.getActionMap().get(DefaultEditorKit.pasteAction));
    edit.add(textComp.getActionMap().get(DefaultEditorKit.selectAllAction));

    return menubar;
  }

  // Subclass can override to use a different open action.
  protected Action getOpenAction() { return openAction; }

  // Subclass can override to use a different save action.
  protected Action getSaveAction() { return saveAction; }

  protected JTextComponent getTextComponent() { return textComp; }

  // ********** ACTION INNER CLASSES ********** //

  // A very simple exit action
  public class ExitAction extends AbstractAction {
    public ExitAction() { super("Exit"); }
    @Override
    public void actionPerformed(ActionEvent ev) { System.exit(0); }
  }

  // An action that opens an existing file
  class OpenAction extends AbstractAction {
    public OpenAction() { 
      super("Open", new ImageIcon("icons/open.gif")); 
    }

    // Query user for a filename and attempt to open and read the file into the
    // text component.
    @Override
    public void actionPerformed(ActionEvent ev) {
      JFileChooser chooser = new JFileChooser();
      if (chooser.showOpenDialog(GrooveEditor.this) !=
          JFileChooser.APPROVE_OPTION)
        return;
      File file = chooser.getSelectedFile();
      if (file == null)
        return;

      FileReader reader = null;
      try {
        reader = new FileReader(file);
        textComp.read(reader, null);
      }
      catch (IOException ex) {
        JOptionPane.showMessageDialog(GrooveEditor.this,
        "File Not Found", "ERROR", JOptionPane.ERROR_MESSAGE);
      }
      finally {
        if (reader != null) {
          try {
            reader.close();
          } catch (IOException x) {}
        }
      }
    }
  }

  // An action that saves the document to a file
  class SaveAction extends AbstractAction {
    public SaveAction() {
      super("Save", new ImageIcon("icons/save.gif"));
    }

    // Query user for a filename and attempt to open and write the text
    // component's content to the file.
    @Override
    public void actionPerformed(ActionEvent ev) {
      JFileChooser chooser = new JFileChooser();
      chooser.addChoosableFileFilter(new FileNameExtensionFilter("Text Document", "txt"));
      chooser.addChoosableFileFilter(new FileNameExtensionFilter("HTML", "html"));

      if (chooser.showSaveDialog(GrooveEditor.this) !=
          JFileChooser.APPROVE_OPTION)
        return;

      @SuppressWarnings("unused")

      String ext = "";
      String extension = chooser.getFileFilter().getDescription();

      if (extension == "txt") {
          ext = ".txt";
      }

      File file = chooser.getSelectedFile();
      if (file == null)
        return;

      FileWriter writer = null;
      try {
        writer = new FileWriter(file);
        textComp.write(writer);
      }
      catch (IOException ex) {
        JOptionPane.showMessageDialog(GrooveEditor.this,
        "File Not Saved", "ERROR", JOptionPane.ERROR_MESSAGE);
      }
      finally {
        if (writer != null) {
          try {
            writer.close();
          } catch (IOException x) {}
        }
      }
    }
  }
}

Answer 1

您需要将文本组件添加到 JScrollPane。例如代替：

content.add(textComp, BorderLayout.CENTER);

使用：

content.add(new JScrollPane(textComp), BorderLayout.CENTER);

有关详细信息，请参阅 How to Use Scroll Panes。

如何将 JTextArea 添加到 JScrollPane？

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