• 背景
• 原始碼分析
  • 1 IModuleManager介面
  • 2 IModuleInitializer介面
  • 3 Run方法
• 總結

背景

  在上篇中我們主要介紹了Prism8中的IModuleInfo和IModuleCatalog介面，通過這兩個介面使我們對Prism框架中的Module有一個比較大概的瞭解，今天這篇文章我們主要來看一下Prism8中的最重要的一個介面IModuleManager這個介面，這個介面對應的實現ModuleManager實現了對整個載入到應用程式中的所有Module進行一個統一的管理，我們來重點看下這個ModuleManager依賴於哪些注入物件以及自身通過實現介面實現了哪些功能？

原始碼分析

1 IModuleManager介面

  我們先來看看這個介面中定義了哪些內容？

/// <summary>
    /// Defines the interface for the service that will retrieve and initialize the application's modules.
    /// </summary>
    public interface IModuleManager
    {
        /// <summary>
        /// Gets all the <see cref="IModuleInfo"/> classes that are in the <see cref="IModuleCatalog"/>.
        /// </summary>
        IEnumerable<IModuleInfo> Modules { get; }

        /// <summary>
        /// Initializes the modules marked as <see cref="InitializationMode.WhenAvailable"/> on the <see cref="IModuleCatalog"/>.
        /// </summary>
        void Run();

        /// <summary>
        /// Loads and initializes the module on the <see cref="IModuleCatalog"/> with the name <paramref name="moduleName"/>.
        /// </summary>
        /// <param name="moduleName">Name of the module requested for initialization.</param>
        void LoadModule(string moduleName);

        /// <summary>
        /// Raised repeatedly to provide progress as modules are downloaded.
        /// </summary>
        event EventHandler<ModuleDownloadProgressChangedEventArgs> ModuleDownloadProgressChanged;

        /// <summary>
        /// Raised when a module is loaded or fails to load.
        /// </summary>
        event EventHandler<LoadModuleCompletedEventArgs> LoadModuleCompleted;
    }
 

  我們可以看到這個裡面第一個定義了一個IEnumerable型別的Modules屬性,這個主要用來描述當前ModuleManager用來管理的所有Modules，第二個Run方法是整個ModuleMananger中實現的核心內容，這個我們後面會重點關注，第三個LoadModule方法用於實現手動Load一個特定名稱的Module,與此相對應的就是LoadModuleCompleted事件這個主要是當前Module進行Load完成後會觸發此事件，另外一個ModuleDownloadProgressChanged事件主要是用來描述當前Module如果是從遠端下載的那麼通過此事件能夠報告當前Module進行下載的Progress，上面我們僅僅是對整個介面定義的功能有一個大概上認知，後面我們將會針對這個裡面的具體細節進行一一描述。
  我們先來看看這個ModuleManager的具體實現類。

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using Prism.Properties;

namespace Prism.Modularity
{
    /// <summary>
    /// Component responsible for coordinating the modules' type loading and module initialization process.
    /// </summary>
    public partial class ModuleManager : IModuleManager, IDisposable
    {
        private readonly IModuleInitializer moduleInitializer;
        private IEnumerable<IModuleTypeLoader> typeLoaders;
        private HashSet<IModuleTypeLoader> subscribedToModuleTypeLoaders = new HashSet<IModuleTypeLoader>();

        /// <summary>
        /// Initializes an instance of the <see cref="ModuleManager"/> class.
        /// </summary>
        /// <param name="moduleInitializer">Service used for initialization of modules.</param>
        /// <param name="moduleCatalog">Catalog that enumerates the modules to be loaded and initialized.</param>
        public ModuleManager(IModuleInitializer moduleInitializer, IModuleCatalog moduleCatalog)
        {
            this.moduleInitializer = moduleInitializer ?? throw new ArgumentNullException(nameof(moduleInitializer));
            ModuleCatalog = moduleCatalog ?? throw new ArgumentNullException(nameof(moduleCatalog));
        }

        /// <summary>
        /// The module catalog specified in the constructor.
        /// </summary>
        protected IModuleCatalog ModuleCatalog { get; }

        /// <summary>
        /// Gets all the <see cref="IModuleInfo"/> classes that are in the <see cref="IModuleCatalog"/>.
        /// </summary>
        public IEnumerable<IModuleInfo> Modules => ModuleCatalog.Modules;

        /// <summary>
        /// Raised repeatedly to provide progress as modules are loaded in the background.
        /// </summary>
        public event EventHandler<ModuleDownloadProgressChangedEventArgs> ModuleDownloadProgressChanged;

        private void RaiseModuleDownloadProgressChanged(ModuleDownloadProgressChangedEventArgs e)
        {
            ModuleDownloadProgressChanged?.Invoke(this, e);
        }

        /// <summary>
        /// Raised when a module is loaded or fails to load.
        /// </summary>
        public event EventHandler<LoadModuleCompletedEventArgs> LoadModuleCompleted;

        private void RaiseLoadModuleCompleted(IModuleInfo moduleInfo, Exception error)
        {
            this.RaiseLoadModuleCompleted(new LoadModuleCompletedEventArgs(moduleInfo, error));
        }

        private void RaiseLoadModuleCompleted(LoadModuleCompletedEventArgs e)
        {
            this.LoadModuleCompleted?.Invoke(this, e);
        }

        /// <summary>
        /// Initializes the modules marked as <see cref="InitializationMode.WhenAvailable"/> on the <see cref="ModuleCatalog"/>.
        /// </summary>
        public void Run()
        {
            this.ModuleCatalog.Initialize();

            this.LoadModulesWhenAvailable();
        }


        /// <summary>
        /// Loads and initializes the module on the <see cref="IModuleCatalog"/> with the name <paramref name="moduleName"/>.
        /// </summary>
        /// <param name="moduleName">Name of the module requested for initialization.</param>
        public void LoadModule(string moduleName)
        {
            var module = this.ModuleCatalog.Modules.Where(m => m.ModuleName == moduleName);
            if (module == null || module.Count() != 1)
            {
                throw new ModuleNotFoundException(moduleName, string.Format(CultureInfo.CurrentCulture, Resources.ModuleNotFound, moduleName));
            }

            var modulesToLoad = this.ModuleCatalog.CompleteListWithDependencies(module);

            this.LoadModuleTypes(modulesToLoad);
        }

        /// <summary>
        /// Checks if the module needs to be retrieved before it's initialized.
        /// </summary>
        /// <param name="moduleInfo">Module that is being checked if needs retrieval.</param>
        /// <returns></returns>
        protected virtual bool ModuleNeedsRetrieval(IModuleInfo moduleInfo)
        {
            if (moduleInfo == null)
                throw new ArgumentNullException(nameof(moduleInfo));

            if (moduleInfo.State == ModuleState.NotStarted)
            {
                // If we can instantiate the type, that means the module's assembly is already loaded into
                // the AppDomain and we don't need to retrieve it.
                bool isAvailable = Type.GetType(moduleInfo.ModuleType) != null;
                if (isAvailable)
                {
                    moduleInfo.State = ModuleState.ReadyForInitialization;
                }

                return !isAvailable;
            }

            return false;
        }

        private void LoadModulesWhenAvailable()
        {
            var whenAvailableModules = this.ModuleCatalog.Modules.Where(m => m.InitializationMode == InitializationMode.WhenAvailable);
            var modulesToLoadTypes = this.ModuleCatalog.CompleteListWithDependencies(whenAvailableModules);
            if (modulesToLoadTypes != null)
            {
                this.LoadModuleTypes(modulesToLoadTypes);
            }
        }

        private void LoadModuleTypes(IEnumerable<IModuleInfo> moduleInfos)
        {
            if (moduleInfos == null)
            {
                return;
            }

            foreach (var moduleInfo in moduleInfos)
            {
                if (moduleInfo.State == ModuleState.NotStarted)
                {
                    if (this.ModuleNeedsRetrieval(moduleInfo))
                    {
                        this.BeginRetrievingModule(moduleInfo);
                    }
                    else
                    {
                        moduleInfo.State = ModuleState.ReadyForInitialization;
                    }
                }
            }

            this.LoadModulesThatAreReadyForLoad();
        }

        /// <summary>
        /// Loads the modules that are not initialized and have their dependencies loaded.
        /// </summary>
        protected virtual void LoadModulesThatAreReadyForLoad()
        {
            bool keepLoading = true;
            while (keepLoading)
            {
                keepLoading = false;
                var availableModules = this.ModuleCatalog.Modules.Where(m => m.State == ModuleState.ReadyForInitialization);

                foreach (var moduleInfo in availableModules)
                {
                    if ((moduleInfo.State != ModuleState.Initialized) && (this.AreDependenciesLoaded(moduleInfo)))
                    {
                        moduleInfo.State = ModuleState.Initializing;
                        this.InitializeModule(moduleInfo);
                        keepLoading = true;
                        break;
                    }
                }
            }
        }

        private void BeginRetrievingModule(IModuleInfo moduleInfo)
        {
            var moduleInfoToLoadType = moduleInfo;
            IModuleTypeLoader moduleTypeLoader = this.GetTypeLoaderForModule(moduleInfoToLoadType);
            moduleInfoToLoadType.State = ModuleState.LoadingTypes;

            // Delegate += works differently between SL and WPF.
            // We only want to subscribe to each instance once.
            if (!this.subscribedToModuleTypeLoaders.Contains(moduleTypeLoader))
            {
                moduleTypeLoader.ModuleDownloadProgressChanged += this.IModuleTypeLoader_ModuleDownloadProgressChanged;
                moduleTypeLoader.LoadModuleCompleted += this.IModuleTypeLoader_LoadModuleCompleted;
                this.subscribedToModuleTypeLoaders.Add(moduleTypeLoader);
            }

            moduleTypeLoader.LoadModuleType(moduleInfo);
        }

        private void IModuleTypeLoader_ModuleDownloadProgressChanged(object sender, ModuleDownloadProgressChangedEventArgs e)
        {
            this.RaiseModuleDownloadProgressChanged(e);
        }

        private void IModuleTypeLoader_LoadModuleCompleted(object sender, LoadModuleCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                if ((e.ModuleInfo.State != ModuleState.Initializing) && (e.ModuleInfo.State != ModuleState.Initialized))
                {
                    e.ModuleInfo.State = ModuleState.ReadyForInitialization;
                }

                // This callback may call back on the UI thread, but we are not guaranteeing it.
                // If you were to add a custom retriever that retrieved in the background, you
                // would need to consider dispatching to the UI thread.
                this.LoadModulesThatAreReadyForLoad();
            }
            else
            {
                this.RaiseLoadModuleCompleted(e);

                // If the error is not handled then I log it and raise an exception.
                if (!e.IsErrorHandled)
                {
                    this.HandleModuleTypeLoadingError(e.ModuleInfo, e.Error);
                }
            }
        }

        /// <summary>
        /// Handles any exception occurred in the module typeloading process,
        /// and throws a <see cref="ModuleTypeLoadingException"/>.
        /// This method can be overridden to provide a different behavior.
        /// </summary>
        /// <param name="moduleInfo">The module metadata where the error happened.</param>
        /// <param name="exception">The exception thrown that is the cause of the current error.</param>
        /// <exception cref="ModuleTypeLoadingException"></exception>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1062:Validate arguments of public methods", MessageId = "1")]
        protected virtual void HandleModuleTypeLoadingError(IModuleInfo moduleInfo, Exception exception)
        {
            if (moduleInfo == null)
                throw new ArgumentNullException(nameof(moduleInfo));


            if (!(exception is ModuleTypeLoadingException moduleTypeLoadingException))
            {
                moduleTypeLoadingException = new ModuleTypeLoadingException(moduleInfo.ModuleName, exception.Message, exception);
            }

            throw moduleTypeLoadingException;
        }

        private bool AreDependenciesLoaded(IModuleInfo moduleInfo)
        {
            var requiredModules = this.ModuleCatalog.GetDependentModules(moduleInfo);
            if (requiredModules == null)
            {
                return true;
            }

            int notReadyRequiredModuleCount =
                requiredModules.Count(requiredModule => requiredModule.State != ModuleState.Initialized);

            return notReadyRequiredModuleCount == 0;
        }

        private IModuleTypeLoader GetTypeLoaderForModule(IModuleInfo moduleInfo)
        {
            foreach (IModuleTypeLoader typeLoader in this.ModuleTypeLoaders)
            {
                if (typeLoader.CanLoadModuleType(moduleInfo))
                {
                    return typeLoader;
                }
            }

            throw new ModuleTypeLoaderNotFoundException(moduleInfo.ModuleName, string.Format(CultureInfo.CurrentCulture, Resources.NoRetrieverCanRetrieveModule, moduleInfo.ModuleName), null);
        }

        private void InitializeModule(IModuleInfo moduleInfo)
        {
            if (moduleInfo.State == ModuleState.Initializing)
            {
                this.moduleInitializer.Initialize(moduleInfo);
                moduleInfo.State = ModuleState.Initialized;
                this.RaiseLoadModuleCompleted(moduleInfo, null);
            }
        }

        #region Implementation of IDisposable

        /// <summary>
        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
        /// </summary>
        /// <remarks>Calls <see cref="Dispose(bool)"/></remarks>.
        /// <filterpriority>2</filterpriority>
        public void Dispose()
        {
            this.Dispose(true);
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Disposes the associated <see cref="IModuleTypeLoader"/>s.
        /// </summary>
        /// <param name="disposing">When <see langword="true"/>, it is being called from the Dispose method.</param>
        protected virtual void Dispose(bool disposing)
        {
            foreach (IModuleTypeLoader typeLoader in this.ModuleTypeLoaders)
            {
                if (typeLoader is IDisposable disposableTypeLoader)
                {
                    disposableTypeLoader.Dispose();
                }
            }
        }

        #endregion
    }
}

看這個大的方法之前我們來看看這個ModuleManager中的建構函式，建構函式包含兩個部分一個是：IModuleInitializer和IModuleCatalog這個裡面IModuleCatalog在上一篇中就此已進行過分析，這裡不在贅述我們先來看看這個IModuleInitializer介面，這個顧名思義就是對介面型別進行初始化操作，我們先來看看這個介面。

2 IModuleInitializer介面

  我們先來看看這個介面的定義

    /// <summary>
    /// Declares a service which initializes the modules into the application.
    /// </summary>
    public interface IModuleInitializer
    {
        /// <summary>
        /// Initializes the specified module.
        /// </summary>
        /// <param name="moduleInfo">The module to initialize</param>
        void Initialize(IModuleInfo moduleInfo);
    }

 通過這個介面定義我們知道這裡面的Initialize方法通過傳入IModuleInfo引數實現對當前傳入IModuleInfo進行初始化，我們來看看這個具體的過程。

using System;
using System.Globalization;
using Prism.Ioc;

namespace Prism.Modularity
{
    /// <summary>
    /// Implements the <see cref="IModuleInitializer"/> interface. Handles loading of a module based on a type.
    /// </summary>
    public class ModuleInitializer : IModuleInitializer
    {
        private readonly IContainerExtension _containerExtension;

        /// <summary>
        /// Initializes a new instance of <see cref="ModuleInitializer"/>.
        /// </summary>
        /// <param name="containerExtension">The container that will be used to resolve the modules by specifying its type.</param>
        public ModuleInitializer(IContainerExtension containerExtension)
        {
            this._containerExtension = containerExtension ?? throw new ArgumentNullException(nameof(containerExtension));
        }

        /// <summary>
        /// Initializes the specified module.
        /// </summary>
        /// <param name="moduleInfo">The module to initialize</param>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes", Justification = "Catches Exception to handle any exception thrown during the initialization process with the HandleModuleInitializationError method.")]
        public void Initialize(IModuleInfo moduleInfo)
        {
            if (moduleInfo == null)
                throw new ArgumentNullException(nameof(moduleInfo));

            IModule moduleInstance = null;
            try
            {
                moduleInstance = this.CreateModule(moduleInfo);
                if (moduleInstance != null)
                {
                    moduleInstance.RegisterTypes(_containerExtension);
                    moduleInstance.OnInitialized(_containerExtension);
                }
            }
            catch (Exception ex)
            {
                this.HandleModuleInitializationError(
                    moduleInfo,
                    moduleInstance?.GetType().Assembly.FullName,
                    ex);
            }
        }

        /// <summary>
        /// Handles any exception occurred in the module Initialization process,
        /// This method can be overridden to provide a different behavior.
        /// </summary>
        /// <param name="moduleInfo">The module metadata where the error happened.</param>
        /// <param name="assemblyName">The assembly name.</param>
        /// <param name="exception">The exception thrown that is the cause of the current error.</param>
        /// <exception cref="ModuleInitializeException"></exception>
        public virtual void HandleModuleInitializationError(IModuleInfo moduleInfo, string assemblyName, Exception exception)
        {
            if (moduleInfo == null)
                throw new ArgumentNullException(nameof(moduleInfo));

            if (exception == null)
                throw new ArgumentNullException(nameof(exception));

            Exception moduleException;

            if (exception is ModuleInitializeException)
            {
                moduleException = exception;
            }
            else
            {
                if (!string.IsNullOrEmpty(assemblyName))
                {
                    moduleException = new ModuleInitializeException(moduleInfo.ModuleName, assemblyName, exception.Message, exception);
                }
                else
                {
                    moduleException = new ModuleInitializeException(moduleInfo.ModuleName, exception.Message, exception);
                }
            }

            throw moduleException;
        }

        /// <summary>
        /// Uses the container to resolve a new <see cref="IModule"/> by specifying its <see cref="Type"/>.
        /// </summary>
        /// <param name="moduleInfo">The module to create.</param>
        /// <returns>A new instance of the module specified by <paramref name="moduleInfo"/>.</returns>
        protected virtual IModule CreateModule(IModuleInfo moduleInfo)
        {
            if (moduleInfo == null)
                throw new ArgumentNullException(nameof(moduleInfo));

            return this.CreateModule(moduleInfo.ModuleType);
        }

        /// <summary>
        /// Uses the container to resolve a new <see cref="IModule"/> by specifying its <see cref="Type"/>.
        /// </summary>
        /// <param name="typeName">The type name to resolve. This type must implement <see cref="IModule"/>.</param>
        /// <returns>A new instance of <paramref name="typeName"/>.</returns>
        protected virtual IModule CreateModule(string typeName)
        {
            Type moduleType = Type.GetType(typeName);
            if (moduleType == null)
            {
                throw new ModuleInitializeException(string.Format(CultureInfo.CurrentCulture, Properties.Resources.FailedToGetType, typeName));
            }

            return (IModule)_containerExtension.Resolve(moduleType);
        }
    }
}

 這個裡面我們發現這個初始化IModuleInfo的核心是根據當前IModuleInfo構造出一個IModule物件，並且呼叫IModule中定義的RegisterTypes和OnInitialized方法，通常在我們的程式碼中我們是這樣使用IModule這個介面的。

using ModuleA.Views;
using Prism.Ioc;
using Prism.Modularity;
using Prism.Regions;

namespace ModuleA
{
    public class ModuleAModule : IModule
    {
        public void OnInitialized(IContainerProvider containerProvider)
        {
            var regionManager = containerProvider.Resolve<IRegionManager>();
            regionManager.RegisterViewWithRegion("ContentRegion", typeof(ViewA));
        }

        public void RegisterTypes(IContainerRegistry containerRegistry)
        {
            
        }
    }
}

  到了這裡我們整個IModuleInitializer介面的作用就全部分析完畢。

3 Run方法

  這個方法是整個ModuleManager中最核心的內容，上面的程式碼貼出來了具體的細節，這裡就這個部分做一個總結：

1. this.ModuleCatalog.Initialize();
    這個ModuleCatalog在上一篇中已經介紹過就是通過Initialize方法將不同的型別的Module逐一進行解析並新增到ModuleCatalog集合中，這個在上一篇中有細緻的說明。
2. LoadModulesWhenAvailable()
    上面一步將整個應用程式中的Module解析並加入到ModuleCatalog中，這一步就是將這些Modules中初始化模式為InitializationMode.WhenAvailable型別的Module進行逐一Load操作，如果當前Module的初始化型別是OnDemand,那麼後面就是需要通過手動呼叫IModuleManager.LoadModule的方法進行手動載入，到了這裡重點就是這個LoadModule到底進行了什麼操作？經過分析程式碼總結如下：

• 通過this.ModuleCatalog.CompleteListWithDependencies方法找到所有InitializationMode.WhenAvailable型別的Module並通過當前方法找到當前Module的所有依賴Module,並形成一個確定的先後載入順序的Module依賴鏈條。
• 確定前一步獲取的Module的狀態是否Ready，如果以及Ready的話執行內部LoadModulesThatAreReadyForLoad()方法
• 如果上面一步Module滿足State未初始化完畢並且其依賴的Module全部初始化完畢則執行IModuleInitializer中的Initialize方法完成對當前IModuleInfo的整個呼叫過程。

總結

 上面的文章以IModuleManager介面為起點進行分析，通過建構函式找到其依賴項，分析其作用，後面通過重點分析Run方法來看ModuleManager是如何初始化整個Module，後面的文章中我們會就其它的一些細節和當前ModuleManager中Run方法呼叫的時機來分析當前ModuleManager的呼叫方是如何控制整個系統的Module運作，至此整個過程將會有一個更加清晰的認知。