#眉標=
#副標=使用Java Swing輕鬆寫個Undoable程式(２)
＃大標＝魔幻四重奏
＃作者＝文／侯捷
#引言=

=============<程式1>=======================
public void undo() throws CannotUndoException {
  if (!canUndo()) {
    throw new CannotUndoException();
  }
  hasBeenDone = false;
}
=============<程式1 end>===============

=======<程式2>=====================
public boolean canUndo() {
  return alive && hasBeenDone;
}
public boolean canRedo() {
  return alive && !hasBeenDone;
}
======<程式2 end>==================

=======<程式3>=======================
public boolean isSignificant() {
	return true;
}
========<程式3 end>=======================

=======<程式4>=========================
public void undo() throws CannotUndoException {
  super.undo();
  int i = edits.size();
  while (i-- > 0) {
	  UndoableEdit e = (UndoableEdit)edits.elementAt(i);
	  e.undo();
  }
}
public void redo() throws CannotRedoException {
  super.redo();
  Enumeration cursor = edits.elements();
  while (cursor.hasMoreElements()) {
	 ((UndoableEdit)cursor.nextElement()).redo();
  }
}
=======<程式4 end >=========================


=============<程式5>==================
public UndoManager() {
    super();
    indexOfNextAdd = 0;
    limit = 100;
    edits.ensureCapacity(limit);
}
public synchronized int getLimit() {
    return limit;
}
public synchronized void setLimit(int l) {
    if (!inProgress) throw …;
    limit = l;
    trimForLimit(); //以索引箭頭為中心左右各減少edits的個數
                       //使總體符合limit範圍內。
}
=========<程式5 end>==================

===========<程式6>=======================
public synchronized void undo() {
    ...
    UndoableEdit edit = editToBeUndone();
    undoTo(edit);
}
protected void undoTo(UndoableEdit edit) {
    boolean done = false;
    while (!done) {
        UndoableEdit next = 
          (UndoableEdit)edits.elementAt(--indexOfNextAdd);
        next.undo();
        done = next == edit;
    }
}

=========<程式6 end>===================


=========<程式7>========================
public static void main(String args[]) {
   ...
  MyPanel myPanel = new MyPanel();

  UndoManager manager = new UndoManager();
  myPanel.addUndoableEditListener(manager);
   ...
==========<程式7 end>==============

=======<程式8>=====================
class MyPanel extends JPanel {
  UndoableEditSupport ues = new UndoableEditSupport(this);
  ...
  public void addUndoableEditListener(UndoableEditListener uel) {
    ues.addUndoableEditListener(uel);
  }
=======<程式8 end>=====================


===========<程式9>=================
public MyPanel() {
    MouseListener mouseListener = new MouseAdapter() {
      public void mouseReleased(MouseEvent mouseEvent) {
        ues.postEdit(new MyUndoableEdit(MyPanel.this));
        ...
      }
    };
    addMouseListener(mouseListener);
}
===========<程式9end>=================

==========<程式10>=========================
public class UndoManager extends CompoundEdit 
                              implements UndoableEditListener {
    ...
    public void undoableEditHappened(UndoableEditEvent e) {
        addEdit(e.getEdit());
    }
}
==========<程式10 end>=========================

======<程式11>====================================
JToolBar toolbar = new JToolBar();
toolbar.add(UndoManagerHelper.getUndoAction(manager));
toolbar.add(UndoManagerHelper.getRedoAction(manager));

//以下建立frame並令其content內含一個toolbar
JFrame frame = new JFrame("Drawing Sample");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container content = frame.getContentPane();
content.add(toolbar, BorderLayout.NORTH);
content.add(drawingPanel, BorderLayout.CENTER);
frame.setSize(300, 150);
frame.setVisible(true);
=======<==========<程式11 end>=========================

===========<程式12>===================
class MyUndoableEdit extends AbstractUndoableEdit {
  MyPanel panel;
  Polygon polygon, savedPolygon;

  public MyUndoableEdit(MyPanel panel) {
    this.panel = panel;
    polygon = panel.getPolygon(); //記錄當時的多邊形
  }
===========<程式12 end>===================

=============<程式13>===================
public MyPanel() {
    MouseListener mouseListener = new MouseAdapter() {
      public void mouseReleased(MouseEvent mouseEvent) {
        ues.postEdit(new MyUndoableEdit(MyPanel.this));

        //以上記錄好當時的多邊形後，才新增頂點並重繪，如下
        polygon.addPoint(mouseEvent.getX(), mouseEvent.getY());
        repaint();
      }
    };
    addMouseListener(mouseListener);
}
=============<程式13 end>===================

========<程式14>=====================
public void undo() throws CannotUndoException {
  super.undo();
  savedPolygon = panel.getPolygon(); //記錄當時的多邊形
  panel.setPolygon(polygon);  //把先前記錄的多邊形拿出來用
}
public void redo() throws CannotRedoException {
  super.redo();
  panel.setPolygon(savedPolygon); //把undo前的多邊形拿出來用
  savedPolygon = null;
}
========<程式14 end>=====================


====<box>===========
#相關資訊
以下是與本文主題相關的書籍資源。
* 《Java Swing》2/e, by Marc Loy, etc. O'Reilly, 2003.
* 《Swing》2/e, by Matthew Robinson & Pavel Vorobive. Manning, 2003.
* 《Definitive Guide to Swing for Java 2》3e, by John Zukowski. APress, 2005
======<BOX END>=========================