设计模式---单例模式（DesignPattern_Single

DesignPattern_AbstractFactory

摘录自：设计模式与游戏完美开发

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SINGLETON—俺有6个漂亮的老婆，她们的老公都是我，我就是我们家里的老公Singleton，她们只要说道“老公”，都是指的同一个人，那就是我(刚才做了个梦啦，哪有这么好的事)
单例模式：单例模式确保某一个类只有一个实例，而且自行实例化并向整个系统提供这个实例单例模式。单例模式只应在有真正的“单一实例”的需求时才可使用。

using UnityEngine;
using System.Collections;

namespace DesignPattern_Singleton
{
    // 单例模式
    public class Singleton
    {
        public string Name {get; set;}

        private static Singleton _instance;
        public static Singleton Instance
        {
            get
            {
                if (_instance == null)
                {
                    Debug.Log("产生Singleton");
                    _instance = new Singleton();                
                }
                return _instance;
            }
        }

        private Singleton(){}
    }
}

using UnityEngine;
using System.Collections;
using DesignPattern_Singleton;

public class SingletonTest : MonoBehaviour {

    // Use this for initialization
    void Start () { 
        UnitTest();
        UnitTest_ClassWithCounter();
    }

    // 单例模式测试方法
    void UnitTest ()
    {       
        Singleton.Instance.Name = "Hello";
        Singleton.Instance.Name = "World";
        Debug.Log (Singleton.Instance.Name);

        //Singleton TempSingleton = new Singleton();// 錯誤  error CS0122: `DesignPattern_Singleton.Singleton.Singleton()' is inaccessible due to its protection level

    }

    // 有计数功能类別的测试方法
    void UnitTest_ClassWithCounter ()
    {
        // 有计数功能的类別
        ClassWithCounter pObj1 = new ClassWithCounter();
        pObj1.Operator();

        ClassWithCounter pObj2 = new ClassWithCounter();
        pObj2.Operator();

        pObj1.Operator();
    }
}

• 一种是具有计数功能的类，来达到单例的效果

using UnityEngine;
using System.Collections;

// 有計數功能的類別
public class ClassWithCounter 
{
    protected static int m_ObjCounter = 0;
    protected bool m_bEnable=false;

    public ClassWithCounter()
    {
        m_ObjCounter++;
        m_bEnable = ( m_ObjCounter ==1 )? true:false ;

        if( m_bEnable==false)
            Debug.LogError("目前物件數["+m_ObjCounter+"]超過1個!!");
    }

    public void Operator()
    {
        if( m_bEnable ==false)
            return ;
        Debug.Log ("可以執行");
    }

}

• 还有一种比较安全的单例写法

public class Singleton
{  
    public const string Name = "Singleton";  
    static Singleton() { }  
    protected Singleton() { }  
    protected static volatile Singleton m_instance = null;  
    protected readonly object m_syncRoot = new object();  
    protected static readonly object m_staticSyncRoot = new object();  
  
    public static Singleton Instance  
    {  
        get  
        {  
            if (m_instance == null)  
            {  
                lock (m_staticSyncRoot)  
                {  
                    if (m_instance == null) m_instance = new Singleton();  
                }  
            }  
            return m_instance;  
        }  
  
        //set { m_instance = value; }  
    }
  
  }

Unity版

public class Singleton
{  
    public const string Name = "Singleton";  
    static Singleton() { }  
    protected Singleton() { }  
    protected static volatile Singleton m_instance = null;  
    protected readonly object m_syncRoot = new object();  
    protected static readonly object m_staticSyncRoot = new object();  
  
    public static Singleton Instance  
    {  
        get  
        {  
            if (m_instance == null)  
            {  
                lock (m_staticSyncRoot)  
                {  
                    if (m_instance == null)
                      {
                        GameObject Obj = new GameObject("Singleton ", typeof(Singleton ));
                        instance = Obj.GetComponent<Singleton >();                        
                      } 
                }  
            }  
            return m_instance;  
        }  
  
        //set { m_instance = value; }  
    }
  
  }