首页 > 代码库 > 高级C#信使（译） - Unity维基百科
高级C#信使（译） - Unity维基百科
高级C#信使
作者：Ilya Suzdalnitski
译自：http://wiki.unity3d.com/index.php/Advanced_CSharp_Messenger
- 描述
- 前言
- MissingReferenceException的原因和解决方案
- 信使
- 用法
- 事件监听器
- 注册事件监听器
- 注销事件监听器
- 广播事件
- 清空信使
- 永久信使
- 杂项
- 打印所有消息
- 从其他信使过渡
- 代码
- Callback.cs
- Messenger.cs
描述
这是C#的一个高级版本的消息系统。当加载了一个新的场景（level）之后，它会自动清空事件表。这将防止程序员意外的调用已销毁的方法，从而有助于防止出现很多MissingReferenceExceptions。这个消息系统是基于Rod Hyde的CSharpMessenger和Magnus Wolffelt的CSharpMessenger Extended而研发的。
前言
我们的项目一旦引入了消息系统（CSharpMessenger Extended），我们就开始面对非常奇怪的BUGs。每次广播一个消息，U3D就会抛出MissingReferenceExceptions这个异常。提示会说消息处理器声明所在类已经被销毁。这个问题无处不在，并且没有一个合理的解释。不过，把消息处理器代码放到try-cache块中可以解决这个问题。我们知道，在代码中有大量的try-cache块不是一个好的解决方案。我们花费了一些时间，终于找到了问题的所在。
MissingReferenceException的原因和解决方案
是这样的，当加载一个新场景（level）（或者重新加载当前场景）时，MissingReferenceException的BUG就会出现。例如：我们有一个消息"start game"，声明如下：
public class MainMenu : MonoBehaviour { void Start () { Messenger.AddListener("start game", StartGame); } void StartGame() { Debug.Log("StartGame called in" + gameObject); //This is the line that would throw an exception } void StartGameButtonPressed() { Messenger.Broadcast("start game"); }}
乍一看，代码完全没有问题。但是在重新加载了这个场景之后，U3D将会抛出一个异常，提示说MainMenu对象已经被销毁。但是没有代码会销毁MainMenu脚本对象。
实际发生的是：
- 我们在信使中添加了一个"start game"消息监听器。
- StartGameButtonPressed方法被调用，广播了"start game"消息。
- 我们使用Application.LoadLevel重新加载了这个场景（level）。
- 重复第1步。
- 重复第2步。
在相应的步骤，信使的事件表里是这个样子的：
- 在第1步：{ "start game", mainMenu1- > StartGame(); }
- 在第4步：{ "start game", mainMenu1- > StartGame(); } { "start game", mainMenu2- > StartGame(); }
所以在第4步我们有两个"start game"消息处理器——第1个是已经销毁的MainMenu对象（在重新加载场景时被销毁），第2个是当前有效的MainMenu对象。结果是这样的，当我们在重新加载场景后广播"start game"消息时，信使把两个消息处理器（已经销毁的和当前有效的）都调用了。这里就是MissingReferenceException出现的源头。 那么解决方法显而易见——在卸载场景之后清空eventTable。在程序员方面不用做任何事来清空这个表，这一过程将自动完成。
信使
我们很高兴向你展示一个高级版本的C#消息系统。
用法
事件监听器
void OnPropCollected( PropType propType ) { if (propType == PropType.Life) livesAmount++;}
注册事件监听器
void Start() { Messenger.AddListener< Prop >( "prop collected", OnPropCollected );}
注销事件监听器
Messenger.RemoveListener< Prop > ( "prop collected", OnPropCollected );
广播事件
public void OnTriggerEnter(Collider _collider) { Messenger.Broadcast< PropType > ( "prop collected", _collider.gameObject.GetComponent<Prop>().propType );}
清空信使
当加载一个新的场景（level）时，信使会自动清空它的eventTable。这将确保信使的eventTable被清空，并且将使我们免于意外的MissingReferenceExceptions。如果你想手动清空管理器的eventTable，你可以调用Messenger.Cleanup()。
永久信使
如果你想要某个消息幸免于Cleanup，使用Messenger.MarkAsPermanent(string)来标记它既可。它可能用于这样的场合：某个类响应不同场景（level）的消息广播。
杂项
打印所有消息
为了调试的目的，你可以把信使的shouldLogAllMessages设置成true。这样，在调用信使的任何方法时都会打印消息。
从其他信使过渡
为了快速把旧的消息系统CSharpMessenger转变成高级的消息系统，请执行下面的步骤：
- 在MonoDevelop中打开“在文件中查找/替换”对话框。
- 在查找域输入：Messenger<([^<>]+)>.([A-Za-z0-9_]+)
- 在替换域输入：Messenger.$2<$1>
- 选择域：所有解决方案
- 勾选“正则搜索”复选框
- 按下“替换”按钮
代码
想要信使顺利运作需要两个文件：Callback.cs和Messenger.cs。
Callback.cs
public delegate void Callback();public delegate void Callback<T>(T arg1);public delegate void Callback<T, U>(T arg1, U arg2);public delegate void Callback<T, U, V>(T arg1, U arg2, V arg3);
Messenger.cs
/* * Advanced C# messenger by Ilya Suzdalnitski. V1.0 * * Based on Rod Hyde‘s "CSharpMessenger" and Magnus Wolffelt‘s "CSharpMessenger Extended". * * Features: * Prevents a MissingReferenceException because of a reference to a destroyed message handler. * Option to log all messages * Extensive error detection, preventing silent bugs * * Usage examples: 1. Messenger.AddListener<GameObject>("prop collected", PropCollected); Messenger.Broadcast<GameObject>("prop collected", prop); 2. Messenger.AddListener<float>("speed changed", SpeedChanged); Messenger.Broadcast<float>("speed changed", 0.5f); * * Messenger cleans up its evenTable automatically upon loading of a new level. * * Don‘t forget that the messages that should survive the cleanup, should be marked with Messenger.MarkAsPermanent(string) * */ //#define LOG_ALL_MESSAGES//#define LOG_ADD_LISTENER//#define LOG_BROADCAST_MESSAGE#define REQUIRE_LISTENER using System;using System.Collections.Generic;using UnityEngine; static internal class Messenger { #region Internal variables //Disable the unused variable warning#pragma warning disable 0414 //Ensures that the MessengerHelper will be created automatically upon start of the game. static private MessengerHelper messengerHelper = ( new GameObject("MessengerHelper") ).AddComponent< MessengerHelper >();#pragma warning restore 0414 static public Dictionary<string, Delegate> eventTable = new Dictionary<string, Delegate>(); //Message handlers that should never be removed, regardless of calling Cleanup static public List< string > permanentMessages = new List< string > (); #endregion #region Helper methods //Marks a certain message as permanent. static public void MarkAsPermanent(string eventType) {#if LOG_ALL_MESSAGES Debug.Log("Messenger MarkAsPermanent \t\"" + eventType + "\"");#endif permanentMessages.Add( eventType ); } static public void Cleanup() {#if LOG_ALL_MESSAGES Debug.Log("MESSENGER Cleanup. Make sure that none of necessary listeners are removed.");#endif List< string > messagesToRemove = new List<string>(); foreach (KeyValuePair<string, Delegate> pair in eventTable) { bool wasFound = false; foreach (string message in permanentMessages) { if (pair.Key == message) { wasFound = true; break; } } if (!wasFound) messagesToRemove.Add( pair.Key ); } foreach (string message in messagesToRemove) { eventTable.Remove( message ); } } static public void PrintEventTable() { Debug.Log("\t\t\t=== MESSENGER PrintEventTable ==="); foreach (KeyValuePair<string, Delegate> pair in eventTable) { Debug.Log("\t\t\t" + pair.Key + "\t\t" + pair.Value); } Debug.Log("\n"); } #endregion #region Message logging and exception throwing static public void OnListenerAdding(string eventType, Delegate listenerBeingAdded) {#if LOG_ALL_MESSAGES || LOG_ADD_LISTENER Debug.Log("MESSENGER OnListenerAdding \t\"" + eventType + "\"\t{" + listenerBeingAdded.Target + " -> " + listenerBeingAdded.Method + "}");#endif if (!eventTable.ContainsKey(eventType)) { eventTable.Add(eventType, null ); } Delegate d = eventTable[eventType]; if (d != null && d.GetType() != listenerBeingAdded.GetType()) { throw new ListenerException(string.Format("Attempting to add listener with inconsistent signature for event type {0}. Current listeners have type {1} and listener being added has type {2}", eventType, d.GetType().Name, listenerBeingAdded.GetType().Name)); } } static public void OnListenerRemoving(string eventType, Delegate listenerBeingRemoved) {#if LOG_ALL_MESSAGES Debug.Log("MESSENGER OnListenerRemoving \t\"" + eventType + "\"\t{" + listenerBeingRemoved.Target + " -> " + listenerBeingRemoved.Method + "}");#endif if (eventTable.ContainsKey(eventType)) { Delegate d = eventTable[eventType]; if (d == null) { throw new ListenerException(string.Format("Attempting to remove listener with for event type \"{0}\" but current listener is null.", eventType)); } else if (d.GetType() != listenerBeingRemoved.GetType()) { throw new ListenerException(string.Format("Attempting to remove listener with inconsistent signature for event type {0}. Current listeners have type {1} and listener being removed has type {2}", eventType, d.GetType().Name, listenerBeingRemoved.GetType().Name)); } } else { throw new ListenerException(string.Format("Attempting to remove listener for type \"{0}\" but Messenger doesn‘t know about this event type.", eventType)); } } static public void OnListenerRemoved(string eventType) { if (eventTable[eventType] == null) { eventTable.Remove(eventType); } } static public void OnBroadcasting(string eventType) {#if REQUIRE_LISTENER if (!eventTable.ContainsKey(eventType)) { throw new BroadcastException(string.Format("Broadcasting message \"{0}\" but no listener found. Try marking the message with Messenger.MarkAsPermanent.", eventType)); }#endif } static public BroadcastException CreateBroadcastSignatureException(string eventType) { return new BroadcastException(string.Format("Broadcasting message \"{0}\" but listeners have a different signature than the broadcaster.", eventType)); } public class BroadcastException : Exception { public BroadcastException(string msg) : base(msg) { } } public class ListenerException : Exception { public ListenerException(string msg) : base(msg) { } } #endregion #region AddListener //No parameters static public void AddListener(string eventType, Callback handler) { OnListenerAdding(eventType, handler); eventTable[eventType] = (Callback)eventTable[eventType] + handler; } //Single parameter static public void AddListener<T>(string eventType, Callback<T> handler) { OnListenerAdding(eventType, handler); eventTable[eventType] = (Callback<T>)eventTable[eventType] + handler; } //Two parameters static public void AddListener<T, U>(string eventType, Callback<T, U> handler) { OnListenerAdding(eventType, handler); eventTable[eventType] = (Callback<T, U>)eventTable[eventType] + handler; } //Three parameters static public void AddListener<T, U, V>(string eventType, Callback<T, U, V> handler) { OnListenerAdding(eventType, handler); eventTable[eventType] = (Callback<T, U, V>)eventTable[eventType] + handler; } #endregion #region RemoveListener //No parameters static public void RemoveListener(string eventType, Callback handler) { OnListenerRemoving(eventType, handler); eventTable[eventType] = (Callback)eventTable[eventType] - handler; OnListenerRemoved(eventType); } //Single parameter static public void RemoveListener<T>(string eventType, Callback<T> handler) { OnListenerRemoving(eventType, handler); eventTable[eventType] = (Callback<T>)eventTable[eventType] - handler; OnListenerRemoved(eventType); } //Two parameters static public void RemoveListener<T, U>(string eventType, Callback<T, U> handler) { OnListenerRemoving(eventType, handler); eventTable[eventType] = (Callback<T, U>)eventTable[eventType] - handler; OnListenerRemoved(eventType); } //Three parameters static public void RemoveListener<T, U, V>(string eventType, Callback<T, U, V> handler) { OnListenerRemoving(eventType, handler); eventTable[eventType] = (Callback<T, U, V>)eventTable[eventType] - handler; OnListenerRemoved(eventType); } #endregion #region Broadcast //No parameters static public void Broadcast(string eventType) {#if LOG_ALL_MESSAGES || LOG_BROADCAST_MESSAGE Debug.Log("MESSENGER\t" + System.DateTime.Now.ToString("hh:mm:ss.fff") + "\t\t\tInvoking \t\"" + eventType + "\"");#endif OnBroadcasting(eventType); Delegate d; if (eventTable.TryGetValue(eventType, out d)) { Callback callback = d as Callback; if (callback != null) { callback(); } else { throw CreateBroadcastSignatureException(eventType); } } } //Single parameter static public void Broadcast<T>(string eventType, T arg1) {#if LOG_ALL_MESSAGES || LOG_BROADCAST_MESSAGE Debug.Log("MESSENGER\t" + System.DateTime.Now.ToString("hh:mm:ss.fff") + "\t\t\tInvoking \t\"" + eventType + "\"");#endif OnBroadcasting(eventType); Delegate d; if (eventTable.TryGetValue(eventType, out d)) { Callback<T> callback = d as Callback<T>; if (callback != null) { callback(arg1); } else { throw CreateBroadcastSignatureException(eventType); } } } //Two parameters static public void Broadcast<T, U>(string eventType, T arg1, U arg2) {#if LOG_ALL_MESSAGES || LOG_BROADCAST_MESSAGE Debug.Log("MESSENGER\t" + System.DateTime.Now.ToString("hh:mm:ss.fff") + "\t\t\tInvoking \t\"" + eventType + "\"");#endif OnBroadcasting(eventType); Delegate d; if (eventTable.TryGetValue(eventType, out d)) { Callback<T, U> callback = d as Callback<T, U>; if (callback != null) { callback(arg1, arg2); } else { throw CreateBroadcastSignatureException(eventType); } } } //Three parameters static public void Broadcast<T, U, V>(string eventType, T arg1, U arg2, V arg3) {#if LOG_ALL_MESSAGES || LOG_BROADCAST_MESSAGE Debug.Log("MESSENGER\t" + System.DateTime.Now.ToString("hh:mm:ss.fff") + "\t\t\tInvoking \t\"" + eventType + "\"");#endif OnBroadcasting(eventType); Delegate d; if (eventTable.TryGetValue(eventType, out d)) { Callback<T, U, V> callback = d as Callback<T, U, V>; if (callback != null) { callback(arg1, arg2, arg3); } else { throw CreateBroadcastSignatureException(eventType); } } } #endregion} //This manager will ensure that the messenger‘s eventTable will be cleaned up upon loading of a new level.public sealed class MessengerHelper : MonoBehaviour { void Awake () { DontDestroyOnLoad(gameObject); } //Clean up eventTable every time a new level loads. public void OnLevelWasLoaded(int unused) { Messenger.Cleanup(); }}
高级C#信使（译） - Unity维基百科
声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉： 投诉/举报 工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。