undoabletextarea.java

java模式之命令模式的一个具体应用

/**
 * 可撤消的文字框类：它是系统的关键部分
 */

package itsukyu;

import java.awt.TextArea;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.TextEvent;
import java.awt.event.TextListener;
import java.util.Hashtable;

import javax.swing.undo.CannotRedoException;
import javax.swing.undo.CannotUndoException;
import javax.swing.undo.StateEdit;
import javax.swing.undo.StateEditable;
import javax.swing.undo.UndoManager;

@SuppressWarnings("serial")
class UndoableTextArea extends TextArea implements StateEditable
{
    private final static String KEY_STATE = "UndoableTextAreaKey"; // hash key
    private boolean textChanged = false;
    private UndoManager undoManager;
    private StateEdit currentEdit;
 
    public UndoableTextArea()
    {
        super();
        initUndoable();
    } 
    public UndoableTextArea(String string)
    {
        super(string);
        initUndoable();
    } 
    public UndoableTextArea(int rows, int columns)
    {
        super(rows, columns);
        initUndoable();
    }
    public UndoableTextArea(String string, int rows, int columns)
    {
        super(string, rows, columns);
        initUndoable();
    } 
    public UndoableTextArea(String string, int rows, int columns, int scrollbars)
    {
        super(string, rows, columns, scrollbars);
        initUndoable();
    } 
 
    // method to undo last edit 
    public boolean undo()
    {
        try
        {
            undoManager.undo();
            return true;
        } 
        catch (CannotUndoException e)
        {
            System.out.println("Can't undo");
            return false;
        } 
    } 
 
    // method to redo last edit 
    public boolean redo()
    {
        try
        {
            undoManager.redo();
            return true;
        } 
        catch (CannotRedoException e)
        {
            System.out.println("Can't redo");
            return false;
        } 
    } 
 
 
    // Implementation of StateEditable interface
    //
    
    // save and restore data to/from hashtable
    public void storeState(Hashtable<Object, Object> state)
    {
        state.put(KEY_STATE, getText());
    } 
    public void restoreState(Hashtable state)
    {
        Object data = state.get(KEY_STATE);
        if (data != null)
        {
            setText((String)data);
        } 
    } 
 
    // Snapshots current edit state
    private void takeSnapshot()
    {
        // snapshot only if text changed
        if (textChanged)
        {
            // end current edit and notify undo manager
            currentEdit.end();
            undoManager.addEdit(currentEdit);
 
            // reset text changed semaphore and create a new current edit
            textChanged = false;
            currentEdit = new StateEdit(this);
        } 
    } 
 
    // Helper method to initialize object to be undoable
    private void initUndoable ()
    {
        // create an undo manager to manage undo operations
        undoManager = new UndoManager();
 
        // create a StateEdit object to represent the current edit
        currentEdit = new StateEdit(this);
 
        // add listeners for various edit-related events
        // use these events to determine when to snapshot current edit
 
        // key listener looks for action keys (non-character keys)
        addKeyListener(new KeyAdapter()
        {
            public void keyPressed(KeyEvent event)
            {
                if (event.isActionKey())
                {
                    // snapshot on any action keys
                    takeSnapshot();
                } 
            } 
        } );
 
        // focus listener looks for loss of focus
        addFocusListener(new FocusAdapter()
        {
            public void focusLost(FocusEvent event)
            {
                // snapshot when control loses focus
                takeSnapshot();
            } 
        } );
 
        // text listener looks for text changes
        addTextListener(new TextListener()
        {
            public void textValueChanged(TextEvent event)
            { 
                textChanged = true;
                
                // snapshot on every change to text
                // might be too granular to be practical
                //
                // this will shapshot every keystroke when typing
                takeSnapshot();
            } 
        } );
    } 
}