原型模式

原型模式就是從一個對象再創建另一個可定製的對象，而不需要知道任何創建的細節。

原型模式本身是比較簡單的，不過其中牽涉到淺複製和深複製的實現，下麵使用.Net自帶的方法和介面分別實現淺複製和深複製：

    public class WorkExperience : ICloneable
    {
        public string workDate;
        public string experience;

        #region ICloneable 成員

        public object Clone()
        {
            //淺複製
            return this.MemberwiseClone();
        }

        #endregion
    }

MemberwiseClone方法實現的是淺複製，即如果欄位是值類型，則對該欄位執行逐位複製，如果欄位是引用類型，則複製引用但不複製引用的對象，因此，原是對象及其複本引用的是同一對象。不過，經過測試發現，對string類型的執行的複製與值類型是相同的，修改新變數中string的值不會影響原變數的值測試如下：

WorkExperience we = new WorkExperience();
we.workDate="today";
we.experience="test";
//輸出為work experience: today, test
Console.WriteLine("work experience: {0},{1}", we.workDate, e.experience);

WorkExperience we2 = (WorkExperience)we.Clone();
we2.experience = "test2";
we2.workDate = "tomorrow";
//輸出為work experience: tomorrow,test2
Console.WriteLine("work experience: {0},{1}", we2.workDate, e2.experience);
//輸出為work experience: today, test
Console.WriteLine("work experience: {0},{1}", we.workDate, we.experience);

下麵演示如何進行深複製和淺複製：

    public class Resume : ICloneable
    {
        public string name;
　　　　 //引用類型，需要區分深複製和淺複製
        public WorkExperience workExperience;

        public Resume(string name)
        {
            this.name = name;
            workExperience = new WorkExperience();
        }

        public void SetExperience(string workDate, string experience)
        {
            workExperience.workDate=workDate;
            workExperience.experience=experience;
        }

        public void Show()
        {
            Console.WriteLine("name : {0}",name);
            Console.WriteLine("work experience: {0},{1}",workExperience.workDate,workExperience.experience);
        }

        /// <summary>
        /// 提供一個私有構造函數，供複製方法使用，以便複製WorkExperience的數據
        /// </summary>
        /// <param name="workExperience"></param>
        private Resume(WorkExperience workExperience)
        {
            this.workExperience = (WorkExperience)workExperience.Clone();
        }

        #region ICloneable 成員

        /// <summary>
        ///深複製，實例化一個新的對象
        /// </summary>
        /// <returns></returns>
        public object Clone()
        {
            Resume newResume = new Resume(this.workExperience);
            newResume.name = this.name;
            return newResume;
        }

        /// <summary>
        /// 淺複製
        /// </summary>
        /// <returns></returns>
        public object Copy()
        {
            return this.MemberwiseClone();
        }

        #endregion
    }

　上例中Clone和Copy分別實現了深複製和淺複製，測試如下：

Resume myResume = new Resume("Kelly");
myResume.SetExperience("2004-2008", "University");
myResume.Show();

//使用淺複製，更改WorkExperience，則被覆制對象也被更改
Resume newResume = (Resume)myResume.Copy();
newResume.SetExperience("2008-2012", "Master Degree");
newResume.name = "Mike";
myResume.Show();

//使用深複製，更改WorkExperience，被覆制對象不會被更改
Resume newResume2 = (Resume)myResume.Clone();
newResume2.SetExperience("2012-now", "Company");
newResume2.name = "Jack";
myResume.Show();

　　運行結果為：

name : Kelly
work experience: 2004-2008,University
name : Kelly
work experience: 2008-2012,Master Degree
name : Kelly
work experience: 2008-2012,Master Degree

可以看出，name由於是string類型，所以始終不會被修改，work experience是引用類型，在第一次做淺複製後被修改，第二次做深複製後沒有被修改。

一般在初始化信息不發生變化的情況下，克隆是最好的辦法，這即隱藏了對象創建的細節，又對性能有很大的提高。