【Unity】中如何统一管理回调函数（利用观察者模式）

2019-11-09 15:42:57

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这次的内容有点类似设计模式里的观察者模式。但是和常规意义上的观察者模式也不是完全一致，所以各位就不要咬文嚼字啦！咦？设计模式？！不懂！没关系，说不定你以前就用过。

开场白

我们来想象一个场景。在加载一个模型时，你需要从网上下载，但是你并不知道下载需要花费多少时间。你所知道的是，当下载完成后，就可以把模型放在特定位置上，开始游戏。那么，我们怎样才能判断下载完成呢？一个简单的方法是，在每一帧的时候都判断下载是否完成，完成后就可以继续后面的工作。因此，我们可以这样做，我们告诉一个管理器，嗨，你帮我盯着点，看下载完了没有，完了就叫我一声，好让我执行XXX函数。我们今天要做的，就是构造这样一个管理器。

实现

注意，下面的代码依赖于之前所讲到的单例模式。我们不防把上面这样一件工作成为一个计数器——Timer（这个名字可能不太恰当），把需要被通知者成为观察者——Oberver，而像下载管理器这样的对象成为一个主题——Subject。首先，我们来定义观察者和主题对象。TimerObserverOrSubject.cs如下：[csharp] view plain copy PRint?using UnityEngine; using System.Collections; public class TimerObserverOrSubject : MonoBehaviour { virtual protected void OnDestroy () { if(Singleton.IsCreatedInstance("TimerController")) { (Singleton.getInstance("TimerController") as TimerController).ClearTimer(this); } } } TimerObserverOrSubject.cs的内容非常简单，它的工作就是在该脚本被析构时，及时地从计数器管理器里面删除涉及这个对象的所有Timer。计数器管理器的脚本——TimerController.cs如下：[csharp] view plain copy print?using UnityEngine; using System.Collections; using System.Collections.Generic; public class TimerController : MonoBehaviour { public delegate void OnCallBack(object arg); public delegate bool OnIsCanDo(object arg); public class Timer { public TimerObserverOrSubject m_Observer; public OnCallBack m_Callback = null; public object m_Arg = null; public TimerObserverOrSubject m_Subject; public OnIsCanDo m_IsCanDoFunc = null; public object m_ArgForIsCanDoFunc = null; public float m_PassTime = 0; public Timer(TimerObserverOrSubject observer, OnCallBack callback, object arg, TimerObserverOrSubject subject, OnIsCanDo isCanDoFunc, object argForIsCanDo) { m_Observer = observer; m_Callback = callback; m_Arg = arg; m_Subject = subject; m_IsCanDoFunc = isCanDoFunc; m_ArgForIsCanDoFunc = argForIsCanDo; m_PassTime = 0; } public Timer(TimerObserverOrSubject observer, OnCallBack callback, object arg, float time) { m_Observer = observer; m_Callback = callback; m_Arg = arg; m_Subject = null; m_IsCanDoFunc = null; m_ArgForIsCanDoFunc = null; m_PassTime = time; } } private List<Timer> m_Timers = new List<Timer>(); private List<Timer> m_NeedRemoveTimer = new List<Timer>(); private List<Timer> m_CurRunTimer = new List<Timer>(); /// <summary> /// Sets the timer. /// </summary> /// <param name='observer'> /// The TimerObserverOrSubject you need to listen /// </param> /// <param name='callback'> /// The callback when condition is true. /// </param> /// <param name='arg'> /// Argument of the callback. /// </param> /// <param name='observer'> /// The TimerObserverOrSubject you need to observe /// </param> /// <param name='isCanDoFunc'> /// The condition function, must return a boolean. /// </param> /// <param name='argForIsCanDo'> /// Argument for condition function. /// </param> public void SetTimer(TimerObserverOrSubject observer, OnCallBack callback ,object arg, TimerObserverOrSubject subject, OnIsCanDo isCanDoFunc,object argForIsCanDo) { if (observer == null || subject == null || callback == null || isCanDoFunc == null) return; if (isCanDoFunc(argForIsCanDo)) { callback(arg); return; } Timer timer = new Timer(observer, callback, arg, subject, isCanDoFunc, argForIsCanDo); m_Timers.Add(timer); } /// <summary> /// Sets the timer. /// </summary> /// <param name='observer'> /// The TimerObserverOrSubject you need to listen /// </param> /// <param name='callback'> /// The callback when time is up. /// </param> /// <param name='arg'> /// Argument of the callback. /// </param> /// <param name='timepass'> /// Timepass before calling the callback. /// </param> public void SetTimer(TimerObserverOrSubject observer, OnCallBack callback , object arg, float timepass) { if (observer != null && callback != null) { Timer timer = new Timer(observer, callback, arg, timepass); m_Timers.Add(timer); } } /// <summary> /// Clears all Timers of the observer. /// </summary> /// <param name='observer'> /// The TimerObserverOrSubject you need to clear /// </param> public void ClearTimer(TimerObserverOrSubject observer) { List<Timer> needRemovedTimers = new List<Timer>(); foreach (Timer timer in m_Timers) { if (timer.m_Observer == observer || timer.m_Subject) { needRemovedTimers.Add(timer); } } foreach (Timer timer in needRemovedTimers) { m_Timers.Remove(timer); } } // Update is called once per frame void Update () { InitialCurTimerDict(); RunTimer(); RemoveTimer(); } private void InitialCurTimerDict() { m_CurRunTimer.Clear(); foreach (Timer timer in m_Timers) { m_CurRunTimer.Add(timer); } } private void RunTimer() { m_NeedRemoveTimer.Clear(); foreach (Timer timer in m_CurRunTimer) { if (timer.m_IsCanDoFunc == null) { timer.m_PassTime = timer.m_PassTime - Time.deltaTime; if (timer.m_PassTime < 0) { timer.m_Callback(timer.m_Arg); m_NeedRemoveTimer.Add(timer); } } else { if (timer.m_IsCanDoFunc(timer.m_ArgForIsCanDoFunc)) { timer.m_Callback(timer.m_Arg); m_NeedRemoveTimer.Add(timer); } } } } private void RemoveTimer() { foreach (Timer timer in m_NeedRemoveTimer) { if (m_Timers.Contains(timer)) { m_Timers.Remove(timer); } } } } 首先，它定义了回调函数的类型：[csharp] view plain copy print?public delegate void OnCallBack(object arg); public delegate bool OnIsCanDo(object arg); 关于C#的委托机制，如果有童鞋不了解，请详见官方文档。简单来说，委托类似一个函数指针，常被用于回调函数。然后，定义了一个数据类型Timer用于保存一个计数器的各个信息。接下来，就是TimerController的两个重要的SetTimer函数。我们先看第一个SetTimer函数：[csharp] view plain copy print?/// <summary> /// Sets the timer. /// </summary> /// <param name='observer'> /// The observer to observe the subject /// </param> /// <param name='callback'> /// The callback when condition is true. /// </param> /// <param name='arg'> /// Argument of the callback. /// </param> /// <param name='subject'> /// The subject you need to observe /// </param> /// <param name='isCanDoFunc'> /// The condition function, must return a boolean. /// </param> /// <param name='argForIsCanDo'> /// Argument for condition function. /// </param> public void SetTimer(TimerObserverOrSubject observer, OnCallBack callback ,object arg, TimerObserverOrSubject subject, OnIsCanDo isCanDoFunc,object argForIsCanDo) { if (observer == null || subject == null || callback == null || isCanDoFunc == null) return; if (isCanDoFunc(argForIsCanDo)) { callback(arg); return; } Timer timer = new Timer(observer, callback, arg, subject, isCanDoFunc, argForIsCanDo); m_Timers.Add(timer); } 根据函数说明可以看出，它负责建立一个计数器，当subject的isCanDoFunc(argForIsCanDo)函数返回true时，通知observer，执行observer的callback(arg)函数。第二个SetTimer函数更简单：[csharp] view plain copy print?/// <summary> /// Sets the timer. /// </summary> /// <param name='observer'> /// The observer to observe the subject /// </param> /// <param name='callback'> /// The callback when time is up. /// </param> /// <param name='arg'> /// Argument of the callback. /// </param> /// <param name='timepass'> /// Timepass before calling the callback. /// </param> public void SetTimer(TimerObserverOrSubject observer, OnCallBack callback , object arg, float timepass) { if (observer != null && callback != null) { Timer timer = new Timer(observer, callback, arg, timepass); m_Timers.Add(timer); } } 它负责建立一个计数器，在timepass的时间后，通知observer，执行observer的callback(arg)函数。Update()函数里面负责检查所有Timer是否可以触发以及是否需要删除。

例子

在这个例子里，我们需要在程序开始运行5秒后，打印一些信息。当然这个的实现有很多方法，这里我们使用今天实现的TimerController来实现。TimerSample.cs的内容如下：[csharp] view plain copy print?using UnityEngine; using System.Collections; public class TimerSample : TimerObserverOrSubject { private TimerController m_TimerCtr = null; private bool m_IsCanDisplay = false; private string m_DisplayContent = "Hello, candycat!"; // Use this for initialization void Start () { m_TimerCtr = Singleton.getInstance("TimerController") as TimerController; //m_TimerCtr.SetTimer(this, Display, m_DisplayContent, 5); m_TimerCtr.SetTimer(this, Display, null, this, IsCanDisplay, null); StartCoroutine(DelayDisplay()); } void Display(object arg) { if (arg == null) { Debug.Log(m_DisplayContent); } else { string content = arg as string; Debug.Log(content); } } bool IsCanDisplay(object arg) { return m_IsCanDisplay; } IEnumerator DelayDisplay() { yield return new WaitForSeconds(5.0f); m_IsCanDisplay = true; } // Update is called once per frame void Update () { } } 首先，它向TimerController请求注册了一个计时器。这里，它的条件是IsCanDisplay函数，它返回bool值m_IsCanDisplay。而这个值将会在5秒后，通过协同函数DelayDisplay来由false置为true。当其为true时，TimerController就将通知TimerSample调用Display函数。我们将第16行代码注释解开，并将18-20行代码注释掉，则可以达到相同的效果。

结束语

C#的委托机制还是非常常用的，使用Unity的童鞋最好还是了解一下。关于TimerController的执行效率，由于它是每一帧都要去判断所有的condition函数，所以应当让condition函数中的逻辑尽可能简单。好了，这次就到这里，如果有更好的想法，或者这里的代码有什么问题，都非常欢迎指正。谢谢阅读！

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