undoredohistory.cs

从设计模式角度介绍了updo redo的实现方法

#region license

/*
Copyright (c) 2007 Lu Yixiang

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
 */

#endregion

#define LIMITED_CAPACITY

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace GenericUndoRedo
{
    /// <summary>
    /// This class represents an undo and redo history.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <seealso cref="IMemento&lt;T&gt;"/>
    [Serializable]
    public class UndoRedoHistory<T>
    {
        private const int DEFAULT_CAPACITY = 100;

        private bool supportRedo = true;
        private bool inUndoRedo = false;

        [NonSerialized]
        private CompoundMemento<T> tempMemento = null;

        /// <summary>
        /// The subject that this undo redo history is about.
        /// </summary>
        protected T subject;

#if LIMITED_CAPACITY
        /// <summary>
        /// Undo stack with capacity
        /// </summary>
        protected RoundStack<IMemento<T>> undoStack;

        /// <summary>
        /// Redo stack with capacity
        /// </summary>
        protected RoundStack<IMemento<T>> redoStack;

        /// <summary>
        /// Creates <see cref="UndoRedoHistory&lt;T&gt;"/> with default capacity.
        /// </summary>
        /// <param name="subject"></param>
        public UndoRedoHistory(T subject)
            : this(subject, DEFAULT_CAPACITY)
        {
        }

        /// <summary>
        /// Creates <see cref="UndoRedoHistory&lt;T&gt;"/> with given capacity.
        /// </summary>
        /// <param name="subject"></param>
        /// <param name="capacity"></param>
        public UndoRedoHistory(T subject, int capacity)
        {
            this.subject = subject;
            undoStack = new RoundStack<IMemento<T>>(capacity);
            redoStack = new RoundStack<IMemento<T>>(capacity);
        }
#else
        /// <summary>
        /// Undo stack
        /// </summary>
        protected Stack<IMemento<T>> undoStack = new Stack<IMemento<T>>(DEFAULT_CAPACITY);

        /// <summary>
        /// Redo stack
        /// </summary>
        protected Stack<IMemento<T>> redoStack = new Stack<IMemento<T>>(DEFAULT_CAPACITY);

        /// <summary>
        /// Creates <see cref="UndoRedoHistory&lt;T&gt;"/>.
        /// </summary>
        /// <param name="subject"></param>
        public UndoRedoHistory(T subject)
        {
            this.subject = subject;
        }
#endif

        /// <summary>
        /// Gets a value indicating if the history is in the process of undoing or redoing.
        /// </summary>
        /// <remarks>
        /// This property is extremely useful to prevent undesired "Do" being executed. 
        /// That could occur in the following scenario:
        /// event X causees a Do action and certain Undo / Redo action causes event X, 
        /// i.e. Undo / Redo causes a Do action, which will render history in a incorrect state.
        /// So whenever <see cref="Do(IMemento&lt;T&gt;)"/> is called, the status of <see cref="InUndoRedo"/> 
        /// should aways be checked first. Example:
        /// <code>
        /// void SomeEventHandler() 
        /// {
        ///     if(!history.InUndoRedo) 
        ///         history.Do(...);
        /// }
        /// </code>
        /// </remarks>
        public bool InUndoRedo
        {
            get { return inUndoRedo; }
        }

        /// <summary>
        /// Gets number of undo actions available
        /// </summary>
        public int UndoCount
        {
            get { return undoStack.Count; }
        }

        /// <summary>
        /// Gets number of redo actions available
        /// </summary>
        public int RedoCount
        {
            get { return redoStack.Count; }
        }

        /// <summary>
        /// Gets or sets whether the history supports redo.
        /// </summary>
        public bool SupportRedo
        {
            get { return supportRedo; }
            set { supportRedo = value; }
        }

        /// <summary>
        /// Begins a complex memento for grouping.
        /// </summary>
        /// <remarks>
        /// From the time this method is called till the time 
        /// <see cref=" EndCompoundDo()"/> is called, all the <i>DO</i> actions (by calling 
        /// <see cref="Do(IMemento&lt;T&gt;)"/>) are added into a temporary 
        /// <see cref="CompoundMemento&lt;T&gt;"/> and this memnto will be pushed into the undo 
        /// stack when <see cref="EndCompoundDo()"/> is called. 
        /// <br/>
        /// If this method is called, it's programmer's responsibility to call <see cref="EndCompoundDo()"/>, 
        /// or else this history will be in incorrect state and stop functioning.
        /// <br/>
        /// Sample Code:
        /// <br/>
        /// <code>
        /// // Version 1: Without grouping
        /// UndoRedoHistory&lt;Foo&gt; history = new UndoRedoHistory&lt;Foo&gt;();
        /// history.Clear();
        /// history.Do(memento1);
        /// history.Do(memento2);
        /// history.Do(memento3);
        /// // history has 3 actions on its undo stack.
        /// 
        /// // Version 1: With grouping
        /// history.BeginCompoundDo(); // starting grouping
        /// history.Do(memento1);
        /// history.Do(memento2);
        /// history.Do(memento3);
        /// hisotry.EndCompoundDo(); // must be called to finish grouping
        /// // history has only 1 action on its undo stack instead 3. 
        /// // This single undo action will undo all actions memorized by memento 1 to 3.
        /// </code>
        /// </remarks>
        /// <exception cref="InvalidOperationException">
        /// Thrown if previous grouping wasn't ended. See <see cref="EndCompoundDo"/>.
        /// </exception>
        /// <seealso cref="EndCompoundDo()"/>
        public void BeginCompoundDo()
        {
            if (tempMemento != null)
                throw new InvalidOperationException("Previous complex memento wasn't commited.");

            tempMemento = new CompoundMemento<T>();
        }

        /// <summary>
        /// Ends grouping by pushing the complext memento created by <see cref="BeginCompoundDo"/> into the undo stack.
        /// </summary>
        /// <remarks>
        /// For details on how <i>grouping</i> works, see <see cref="BeginCompoundDo"/>.
        /// </remarks>
        /// <exception cref="InvalidOperationException">
        /// Thrown if grouping wasn't started. See <see cref="BeginCompoundDo"/>.
        /// </exception>/// <seealso cref="BeginCompoundDo()"/>
        public void EndCompoundDo()
        {
            if (tempMemento == null)
                throw new InvalidOperationException("Ending a non-existing complex memento");

            _Do(tempMemento);
            tempMemento = null;
        }

        /// <summary>
        /// Pushes an memento into the undo stack, any time the state of <see cref="subject"/> changes. 
        /// </summary>
        /// <param name="m"></param>
        /// <remarks>
        /// This method MUST be properly involked by programmers right before (preferably) or right after 
        /// the state of <see cref="subject"/> is changed. 
        /// Whenever <see cref="Do(IMemento&lt;T&gt;)"/> is called, the status of <see cref="InUndoRedo"/> 
        /// should aways be checked first. See details at <see cref="InUndoRedo"/>. 
        /// This method causes redo stack to be cleared.
        /// </remarks>
        /// <seealso cref="InUndoRedo"/>
        /// <seealso cref="Undo()"/>
        /// <seealso cref="Redo()"/>
        public void Do(IMemento<T> m)
        {
            if (inUndoRedo)
                throw new InvalidOperationException("Involking do within an undo/redo action.");

            if (tempMemento == null)
            {
                _Do(m);
            }
            else
            {
                tempMemento.Add(m);
            }
        }

        /// <summary>
        /// Internal <b>DO</b> action with no error checking
        /// </summary>
        /// <param name="m"></param>
        private void _Do(IMemento<T> m)
        {
            redoStack.Clear();
            undoStack.Push(m);
        }

        /// <summary>
        /// Restores the subject to the previous state on the undo stack, and stores the state before undoing to redo stack.
        /// Method <see cref="CanUndo()"/> can be called before calling this method.
        /// </summary>
        /// <seealso cref="Redo()"/>
        public void Undo()
        {
            if (tempMemento != null)
                throw new InvalidOperationException("The complex memento wasn't commited.");

            inUndoRedo = true;
            IMemento<T> top = undoStack.Pop();
            redoStack.Push(top.Restore(subject));
            inUndoRedo = false;
        }

        /// <summary>
        /// Restores the subject to the next state on the redo stack, and stores the state before redoing to undo stack. 
        /// Method <see cref="CanRedo()"/> can be called before calling this method.
        /// </summary>
        /// <seealso cref="Undo()"/>
        public void Redo()
        {
            if (tempMemento != null)
                throw new InvalidOperationException("The complex memento wasn't commited.");

            inUndoRedo = true;
            IMemento<T> top = redoStack.Pop();
            undoStack.Push(top.Restore(subject));
            inUndoRedo = false;
        }

        /// <summary>
        /// Checks if there are any stored state available on the undo stack.
        /// </summary>
        public bool CanUndo
        {
            get { return (undoStack.Count != 0); }
        }

        /// <summary>
        /// Checks if there are any stored state available on the redo stack.
        /// </summary>
        public bool CanRedo
        {
            get { return (redoStack.Count != 0); }
        }

        /// <summary>
        /// Clear the entire undo and redo stacks.
        /// </summary>
        public void Clear()
        {
            undoStack.Clear();
            redoStack.Clear();
        }

        /// <summary>
        /// Gets, without removing, the top memento on the undo stack.
        /// </summary>
        /// <returns></returns>
        public IMemento<T> PeekUndo()
        {
            if (undoStack.Count > 0)
                return undoStack.Peek();
            else
                return null;
        }

        /// <summary>
        /// Gets, without removing, the top memento on the redo stack.
        /// </summary>
        /// <returns></returns>
        public IMemento<T> PeekRedo()
        {
            if (redoStack.Count > 0)
                return redoStack.Peek();
            else
                return null;
        }

    }

}