如果你想让继承MonoBehaviour的类变成Singleten

单例是指只有一个实例的类

通常创建单例的方法是

using System;
public class Singleton
{
private static Singleton instance;
private Singleton() {}
public static Singleton Instance
{
get
{
if (instance == null)
{
instance = new Singleton();
}
return instance;
}
}
}
但是由于MonoBehaviour中不能用new，不能从一个构造函数初始化，所以上面这段代码要改写成
using System;
public class Singleton ：MonoBehavior
{
private static Singleton instance;
public static Singleton Instance
{
return instance;
}
void Awake()
{
instance = this;
}
}
现在回过头来看通常方法有什么优点和缺点

优点
1.由于实例是在Instance属性方法内部创建的，因此类可以使用附加功能（例如，对子类进行实例化），即使它可能引入不想要的依赖性。
2.直到对象要求产生一个实例才执行实例化；这种方法称为“懒实例化”。懒实例化避免了在应用程序启动时实例化不必要的singleton。

缺点
在多线程环境下是不安全的。如果执行过程的不同线程同时进入Instance属性方法，那么可能会创建多个Singleton对象实例。

解决方法——静态初始化

public sealed class Singleton
{
private static readonly Singleton instance = new Singleton();
private Singleton(){}
public static Singleton Instance
{
get
{
return instance;
}
}
}
在此策略中，将在第一次引用类的任何成员时创建实例。
sealed阻止派生。
变量标记为readonly，意味着只能在静态初始化期间或在类构造函数中分配变量。

多线程Singleton

下面的实现仅允许一个线程在尚未创建 Singleton 实例的情况下进入关键区域（该区域由 lock 块标识）。

using System;
public sealed class Singleton
{
private static volatile Singleton instance;
private static object syncRoot = new Object();
private Singleton() {}
public static Singleton Instance
{
get
{
if (instance == null)
{
lock (syncRoot)
{
if (instance == null)
instance = new Singleton();
}
}
return instance;
}
}
}
http://msdn.microsoft.com/zh-cn/library/ff650316.aspx

下面是一个不使用Awake实现单例化并继承MonoBehavior的例子

using UnityEngine;
using System.Collections;

/// <summary>
/// MONOBEHAVIOR PSEUDO SINGLETON ABSTRACT CLASS
/// usage : best is to be attached to a gameobject but if not that is ok,
/// : this will create one on first access
/// example : '''public sealed class MyClass : Singleton<MyClass> {'''
/// references : http://tinyurl.com/d498g8c /// : http://tinyurl.com/cc73a9h /// : http://unifycommunity.com/wiki/index.php?title=Singleton /// </summary>
public abstract class Singleton<T> : MonoBehaviour where T : MonoBehaviour
{

private static T _instance = null;

/// <summary>
/// gets the instance of this Singleton
/// use this for all instance calls:
/// MyClass.Instance.MyMethod();
/// or make your public methods static
/// and have them use Instance
/// </summary>
public static T Instance {
get {
if (_instance == null) {
_instance = (T)FindObjectOfType (typeof(T));
if (_instance == null) {

string goName = typeof(T).ToString ();

GameObject go = GameObject.Find (goName);
if (go == null) {
go = new GameObject ();
go.name = goName;
}

_instance = go.AddComponent<T> ();
}
}
return _instance;
}
}

/// <summary>
/// for garbage collection
/// </summary>
public virtual void OnApplicationQuit ()
{
// release reference on exit
_instance = null;
}

// in your child class you can implement Awake()
// and add any initialization code you want such as
// DontDestroyOnLoad(go);
// if you want this to persist across loads
// or if you want to set a parent object with SetParent()

/// <summary>
/// parent this to another gameobject by string
/// call from Awake if you so desire
/// </summary>
protected void SetParent (string parentGOName)
{
if (parentGOName != null) {
GameObject parentGO = GameObject.Find (parentGOName);
if (parentGO == null) {
parentGO = new GameObject ();
parentGO.name = parentGOName;
}
this.transform.parent = parentGO.transform;
}
}
}