由于对单例理解的不是很深，所以在我的印象中，例就是一个比较有规范的全局类。
至于什么多线程可能会有问题，我暂时没接触到。
1.首先是最简单的了，各种语言都可以写的单例
C#：
public class ExpManager {
static ExpManager m_ExpManager = null;
public static ExpManager GetSingleton() { if (null == m_ExpManager) { m_ExpManager = new ExpManager(); } return m_ExpManager; } }
2.Unity中的单例
在Unity中场景的概念分的比较明显，经常有场景间的跳转，而在跳转时会把上一个场景的东西销毁，再创建下一个场景的东西。
但有些东西却是场景共用的，比如说共用的UI，声音播放器等。这时我们就想要一个不会被销毁的东西来承载这些东西。
Unity提供了这个函数：
http://docs.unity3d.com/Documentation/ScriptReference/Object.DontDestroyOnLoad.html
在NGUI中看UpdateManager这个类，可以看到他的单例的实现，还有如何管理自己的Update函数，比如计时器实现时也要用到Update：
public class UpdateManager : MonoBehaviour { public delegate void OnUpdate (float delta); public class UpdateEntry { public int index = 0; public OnUpdate func; public MonoBehaviour mb; public bool isMonoBehaviour = false; } public class DestroyEntry { public Object obj; public float time; } static int Compare (UpdateEntry a, UpdateEntry b) { if (a.index < b.index) return 1; if (a.index > b.index) return 1; return 0; } static UpdateManager mInst; List<UpdateEntry> mOnUpdate = new List<UpdateEntry>(); List<UpdateEntry> mOnLate = new List<UpdateEntry>(); List<UpdateEntry> mOnCoro = new List<UpdateEntry>(); BetterList<DestroyEntry> mDest = new BetterList<DestroyEntry>(); float mTime = 0f; /// <summary> /// Ensure that there is an instance of this class present. /// </summary> static void CreateInstance () { if (mInst == null) { mInst = GameObject.FindObjectOfType(typeof(UpdateManager)) as UpdateManager; if (mInst == null && Application.isPlaying) { GameObject go = new GameObject("_UpdateManager"); DontDestroyOnLoad(go); //go.hideFlags = HideFlags.HideAndDontSave; mInst = go.AddComponent<UpdateManager>(); } } } /// <summary> /// Update the specified list. /// </summary> void UpdateList (List<UpdateEntry> list, float delta) { for (int i = list.Count; i > 0; ) { UpdateEntry ent = list[--i]; // If it's a monobehaviour we need to do additional checks if (ent.isMonoBehaviour) { // If the monobehaviour is null, remove this entry if (ent.mb == null) { list.RemoveAt(i); continue; } // If the monobehaviour or its game object are disabled, move on to the next entry if (!ent.mb.enabled || !ent.mb.gameObject.active) continue; } // Call the function ent.func(delta); } } /// <summary> /// Start the coroutine. /// </summary> void Start () { if (Application.isPlaying) { mTime = Time.realtimeSinceStartup; StartCoroutine(CoroutineFunction()); } } /// <summary> /// Don't keep this class around after stopping the Play mode. /// </summary> void OnApplicationQuit () { DestroyImmediate(gameObject); } /// <summary> /// Call all update functions. /// </summary> void Update () { if (mInst != this) NGUITools.Destroy(gameObject); else UpdateList(mOnUpdate, Time.deltaTime); } /// <summary> /// Call all late update functions and destroy this class if no callbacks have been registered. /// </summary> void LateUpdate () { UpdateList(mOnLate, Time.deltaTime); if (!Application.isPlaying) CoroutineUpdate(); } /// <summary> /// Call all coroutine update functions and destroy all delayed destroy objects. /// </summary> bool CoroutineUpdate () { float time = Time.realtimeSinceStartup; float delta = time - mTime; if (delta < 0.001f) return true; mTime = time; UpdateList(mOnCoro, delta); bool appIsPlaying = Application.isPlaying; for (int i = mDest.size; i > 0; ) { DestroyEntry de = mDest.buffer[--i]; if (!appIsPlaying || de.time < mTime) { if (de.obj != null) { NGUITools.Destroy(de.obj); de.obj = null; } mDest.RemoveAt(i); } } // Nothing left to update? Destroy this game object. if (mOnUpdate.Count == 0 && mOnLate.Count == 0 && mOnCoro.Count == 0 && mDest.size == 0) { NGUITools.Destroy(gameObject); return false; } return true; } /// <summary> /// Coroutine update function. /// </summary> IEnumerator CoroutineFunction () { while (Application.isPlaying) { if (CoroutineUpdate()) yield return null; else break; } } /// <summary> /// Generic add function. /// Technically 'mb' is not necessary as it can be retrieved by calling 'func.Target as MonoBehaviour'. /// Unfortunately Flash export fails to compile with that, claiming the following: /// "Error: Access of possibly undefined property Target through a reference with static type Function." /// </summary> void Add (MonoBehaviour mb, int updateOrder, OnUpdate func, List<UpdateEntry> list) { #if !UNITY_FLASH // Flash export fails at life. for (int i = 0, imax = list.Count; i < imax; ++i) { UpdateEntry ent = list[i]; if (ent.func == func) return; } #endif UpdateEntry item = new UpdateEntry(); item.index = updateOrder; item.func = func; item.mb = mb; item.isMonoBehaviour = (mb != null); list.Add(item); if (updateOrder != 0) list.Sort(Compare); } /// <summary> /// Add a new update function with the specified update order. /// </summary> static public void AddUpdate (MonoBehaviour mb, int updateOrder, OnUpdate func) { CreateInstance(); mInst.Add(mb, updateOrder, func, mInst.mOnUpdate); } /// <summary> /// Add a new late update function with the specified update order. /// </summary> static public void AddLateUpdate (MonoBehaviour mb, int updateOrder, OnUpdate func) { CreateInstance(); mInst.Add(mb, updateOrder, func, mInst.mOnLate); } /// <summary> /// Add a new coroutine update function with the specified update order. /// </summary> static public void AddCoroutine (MonoBehaviour mb, int updateOrder, OnUpdate func) { CreateInstance(); mInst.Add(mb, updateOrder, func, mInst.mOnCoro); } /// <summary> /// Destroy the object after the specified delay in seconds. /// </summary> static public void AddDestroy (Object obj, float delay) { if (obj == null) return; if (Application.isPlaying) { if (delay > 0f) { CreateInstance(); DestroyEntry item = new DestroyEntry(); item.obj = obj; item.time = Time.realtimeSinceStartup + delay; mInst.mDest.Add(item); } else Destroy(obj); } else DestroyImmediate(obj); } }
