高級C#信使（譯） - Unity維基百科

時間 2019-11-13

標籤高級 c# 信使 unity 維基百科欄目 C# 简体版

原文原文鏈接

高級C#信使

做者：Ilya Suzdalnitskiphp

譯自：http://wiki.unity3d.com/index.php/Advanced_CSharp_Messenger程序員

描述

這是C#的一個高級版本的消息系統。當加載了一個新的場景（level）以後，它會自動清空事件表。這將防止程序員意外的調用已銷燬的方法，從而有助於防止出現不少MissingReferenceExceptions。這個消息系統是基於Rod Hyde的CSharpMessenger和Magnus Wolffelt的CSharpMessenger Extended而研發的。less

前言

咱們的項目一旦引入了消息系統（CSharpMessenger Extended），咱們就開始面對很是奇怪的BUGs。每次廣播一個消息，U3D就會拋出MissingReferenceExceptions這個異常。提示會說消息處理器聲明所在類已經被銷燬。這個問題無處不在，而且沒有一個合理的解釋。不過，把消息處理器代碼放到try-cache塊中能夠解決這個問題。咱們知道，在代碼中有大量的try-cache塊不是一個好的解決方案。咱們花費了一些時間，終於找到了問題的所在。ide

MissingReferenceException的緣由和解決方案

是這樣的，當加載一個新場景（level）（或者從新加載當前場景）時，MissingReferenceException的BUG就會出現。例如：咱們有一個消息"start game"，聲明以下：this

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，代碼徹底沒有問題。可是在從新加載了這個場景以後，U3D將會拋出一個異常，提示說MainMenu對象已經被銷燬。可是沒有代碼會銷燬MainMenu腳本對象。spa

實際發生的是：3d

咱們在信使中添加了一個"start game"消息監聽器。
StartGameButtonPressed方法被調用，廣播了"start game"消息。
咱們使用Application.LoadLevel從新加載了這個場景（level）。
重複第1步。
重複第2步。

在相應的步驟，信使的事件表裏是這個樣子的：調試

在第1步：{ "start game", mainMenu1- > StartGame(); }
在第4步：{ "start game", mainMenu1- > StartGame(); } { "start game", mainMenu2- > StartGame(); }

因此在第4步咱們有兩個"start game"消息處理器——第1個是已經銷燬的MainMenu對象（在從新加載場景時被銷燬），第2個是當前有效的MainMenu對象。結果是這樣的，當咱們在從新加載場景後廣播"start game"消息時，信使把兩個消息處理器（已經銷燬的和當前有效的）都調用了。這裏就是MissingReferenceException出現的源頭。那麼解決方法顯而易見——在卸載場景以後清空eventTable。在程序員方面不用作任何事來清空這個表，這一過程將自動完成。 rest

信使

咱們很高興向你展現一個高級版本的C#消息系統。 code

用法

事件監聽器

void OnPropCollected( PropType propType ) {
    if (propType == PropType.Life)
        livesAmount++;
}

註冊事件監聽器

void Start() {
    Messenger.AddListener< Prop >( "prop collected", OnPropCollected );
}

註銷事件監聽器

    Messenger.RemoveListener< Prop > ( "prop collected", OnPropCollected );

廣播事件

public void OnTriggerEnter(Collider _collider) 
{
    Messenger.Broadcast< PropType > ( "prop collected", _collider.gameObject.GetComponent<Prop>().propType );
}

清空信使

當加載一個新的場景（level）時，信使會自動清空它的eventTable。這將確保信使的eventTable被清空，而且將使咱們免於意外的MissingReferenceExceptions。若是你想手動清空管理器的eventTable，你能夠調用Messenger.Cleanup()。

永久信使

若是你想要某個消息倖免於Cleanup，使用Messenger.MarkAsPermanent(string)來標記它既可。它可能用於這樣的場合：某個類響應不一樣場景（level）的消息廣播。

雜項

打印全部消息

爲了調試的目的，你能夠把信使的shouldLogAllMessages設置成true。這樣，在調用信使的任何方法時都會打印消息。

從其餘信使過渡

爲了快速把舊的消息系統CSharpMessenger轉變成高級的消息系統，請執行下面的步驟：

在MonoDevelop中打開「在文件中查找/替換」對話框。
在查找域輸入：Messenger<([^<>]+)>.([A-Za-z0-9_]+)
在替換域輸入：Messenger.$2<$1>
選擇域：全部解決方案
勾選「正則搜索」複選框
按下「替換」按鈕

代碼

想要信使順利運做須要兩個文件：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();
    }
}

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