Prism中如何控制模块初始化的顺序

Question

我将 Prism V2 与 DirectoryModuleCatalog 一起使用，并且需要按特定顺序初始化模块。所需的顺序由每个 IModule 实现上的属性指定。

这样，当每个模块初始化时，它们会将其视图添加到 TabControl 区域中，并且选项卡的顺序需要确定并由模块作者控制。

该顺序并不意味着依赖关系，而只是它们初始化的顺序。换句话说：模块 A、B 和 C 的优先级可能分别为 1、2 和 3。 B 不依赖于 A - 它只需要在 A 之后加载到 TabControl 区域中。这样我们就有了确定且可控的选项卡顺序。另外，B 在运行时可能不存在；因此它们将加载为 A, C，因为优先级应确定顺序 (1, 3)。如果我使用 ModuleDependency，那么模块“C”将无法加载其所有依赖项。

我可以管理如何对模块进行排序的逻辑，但我无法弄清楚将所述逻辑放在哪里。

Answer 1

我不喜欢使用 ModuleDependency 的想法，因为这意味着当模块 b 不存在时，模块 a 不会加载，而实际上没有依赖项。相反，我创建了一个优先级属性来装饰模块：

/// <summary>
/// Allows the order of module loading to be controlled.  Where dependencies
/// allow, module loading order will be controlled by relative values of priority
/// </summary>
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public sealed class PriorityAttribute : Attribute
{
    /// <summary>
    /// Constructor
    /// </summary>
    /// <param name="priority">the priority to assign</param>
    public PriorityAttribute(int priority)
    {
        this.Priority = priority;
    }

    /// <summary>
    /// Gets or sets the priority of the module.
    /// </summary>
    /// <value>The priority of the module.</value>
    public int Priority { get; private set; }
}

然后我像这样装饰模块：

[Priority(200)]
[Module(ModuleName = "MyModule")]
public class MyModule : IModule

我创建了 DirectoryModuleCatalog 的新后代：

/// <summary>
/// ModuleCatalog that respects PriorityAttribute for sorting modules
/// </summary>
[SecurityPermission(SecurityAction.InheritanceDemand), SecurityPermission(SecurityAction.LinkDemand)]
public class PrioritizedDirectoryModuleCatalog : DirectoryModuleCatalog
{
    /// <summary>
    /// local class to load assemblies into different appdomain which is then discarded
    /// </summary>
    private class ModulePriorityLoader : MarshalByRefObject
    {
        /// <summary>
        /// Get the priorities
        /// </summary>
        /// <param name="modules"></param>
        /// <returns></returns>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic"), System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Reliability", "CA2001:AvoidCallingProblematicMethods", MessageId = "System.Reflection.Assembly.LoadFrom")]
        public Dictionary<string, int> GetPriorities(IEnumerable<ModuleInfo> modules)
        {
            //retrieve the priorities of each module, so that we can use them to override the 
            //sorting - but only so far as we don't mess up the dependencies
            var priorities = new Dictionary<string, int>();
            var assemblies = new Dictionary<string, Assembly>();

            foreach (ModuleInfo module in modules)
            {
                if (!assemblies.ContainsKey(module.Ref))
                {
                    //LoadFrom should generally be avoided appently due to unexpected side effects,
                    //but since we are doing all this in a separate AppDomain which is discarded
                    //this needn't worry us
                    assemblies.Add(module.Ref, Assembly.LoadFrom(module.Ref));
                }

                Type type = assemblies[module.Ref].GetExportedTypes()
                    .Where(t => t.AssemblyQualifiedName.Equals(module.ModuleType, StringComparison.Ordinal))
                    .First();

                var priorityAttribute =
                    CustomAttributeData.GetCustomAttributes(type).FirstOrDefault(
                        cad => cad.Constructor.DeclaringType.FullName == typeof(PriorityAttribute).FullName);

                int priority;
                if (priorityAttribute != null)
                {
                    priority = (int)priorityAttribute.ConstructorArguments[0].Value;
                }
                else
                {
                    priority = 0;
                }

                priorities.Add(module.ModuleName, priority);
            }

            return priorities;
        }
    }

    /// <summary>
    /// Get the priorities that have been assigned to each module.  If a module does not have a priority 
    /// assigned (via the Priority attribute) then it is assigned a priority of 0
    /// </summary>
    /// <param name="modules">modules to retrieve priorities for</param>
    /// <returns></returns>
    private Dictionary<string, int> GetModulePriorities(IEnumerable<ModuleInfo> modules)
    {
        AppDomain childDomain = BuildChildDomain(AppDomain.CurrentDomain);
        try
        {
            Type loaderType = typeof(ModulePriorityLoader);
            var loader =
                (ModulePriorityLoader)
                childDomain.CreateInstanceFrom(loaderType.Assembly.Location, loaderType.FullName).Unwrap();

            return loader.GetPriorities(modules);
        }
        finally
        {
            AppDomain.Unload(childDomain);
        }
    }

    /// <summary>
    /// Sort modules according to dependencies and Priority
    /// </summary>
    /// <param name="modules">modules to sort</param>
    /// <returns>sorted modules</returns>
    protected override IEnumerable<ModuleInfo> Sort(IEnumerable<ModuleInfo> modules)
    {
        Dictionary<string, int> priorities = GetModulePriorities(modules);
        //call the base sort since it resolves dependencies, then re-sort 
        var result = new List<ModuleInfo>(base.Sort(modules));
        result.Sort((x, y) =>
            {
                string xModuleName = x.ModuleName;
                string yModuleName = y.ModuleName;
                //if one depends on other then non-dependent must come first
                //otherwise base on priority
                if (x.DependsOn.Contains(yModuleName))
                    return 1; //x after y
                else if (y.DependsOn.Contains(xModuleName))
                    return -1; //y after x
                else 
                    return priorities[xModuleName].CompareTo(priorities[yModuleName]);
            });

        return result;
    }
}

最后，我更改了引导程序以使用这个新目录：

    /// <summary>Where are the modules located</summary>
    /// <returns></returns>
    protected override IModuleCatalog GetModuleCatalog()
    {
        return new PrioritizedDirectoryModuleCatalog() { ModulePath = @".\Modules" };
    }

我不确定是否带有程序集加载的内容是最好的做事方式，但它似乎有效......

Answer 2

您可以在模块类上使用 ModuleDependency 属性来告诉加载器您的模块依赖于其他模块：

[ModuleDependency("SomeModule")]
[ModuleDependency("SomeOtherModule")]
public class MyModule : IModule
{
}

Answer 3

您可以将默认的IModuleInitializer替换为自定义类的实例，该实例不是在加载模块后立即对其进行初始化，而是将它们存储在模块列表中。加载所有模块后，您可以按照您想要的顺序初始化它们。

如何实现这一点：

1) 在引导程序中，重写 ConfigureContainer 方法来替换 MyModuleInitializer 类实例的默认 IModuleInitializer，但使用名称维护默认初始化程序（例如，defaultModuleInitializer）：

protected override void ConfigureContainer()
{
    base.ConfigureContainer();
    var defaultContainer = Container.Resolve<IModuleInitializer>();
    Container.RegisterInstance<IModuleInitializer>("defaultModuleInitializer", defaultContainer);
    Container.RegisterType<IModuleInitializer, MyModuleInitializer>(new ContainerControlledLifetimeManager());
}

2) 创建执行所需的 storea-all-then-sort-and-initialize 过程的 MyModuleInitializer 类：

public class MyModuleInitializer : IModuleInitializer
{
    bool initialModuleLoadCompleted = false;
    IModuleInitializer defaultInitializer = null;
    List<ModuleInfo> modules = new List<ModuleInfo>();

    public MyModuleInitializer(IUnityContainer container)
    {
        defaultInitializer = container.Resolve<IModuleInitializer>("defaultModuleInitializer");
    }

    public void Initialize(ModuleInfo moduleInfo)
    {
        if(initialModuleLoadCompleted) {
            //Module loaded on demand after application startup - use the default initializer
            defaultInitializer.Initialize(moduleInfo);
            return;
        }

        modules.Add(moduleInfo);

        if(AllModulesLoaded()) {
            SortModules();
            foreach(var module in modules) {
                defaultInitializer.Initialize(module);
            }
            modules = null;
            initialModuleLoadCompleted = true;
        }
    }

    private bool AllModulesLoaded()
    {
        //Here you check whether all the startup modules have been loaded
        //(perhaps by looking at the module catalog) and return true if so
    }

    private void SortModules()
    {
        //Here you sort the "modules" list however you want
    }
}

请注意，加载所有启动模块后，此类将恢复为简单地调用默认初始化程序。如果这不是您所需要的，请适当调整课程。

Answer 4

我通过使用 ModuleDependency 属性解决了这个问题，它的作用就像一个魅力

Answer 5

在 Bootstrapper 的 AddModule() 调用中，您可以指定依赖项。因此，您可以说 A 依赖于 B 依赖于 C，这将决定加载顺序。

http://msdn.microsoft.com/en-us/magazine/cc785479。 ASPX

Answer 6

让这个起死回生，因为我似乎找到了一个不同的解决方案，有些人可能会觉得有用。我尝试了一下，它有效，但我还没有摸索出所有的优点和缺点。

我使用 DirectoryModuleCatalog 来获取所有模块的列表，这些模块全部放入一个文件夹中。但我注意到，在大多数情况下，我的所有“视图”模块都依赖于我的“服务”模块，这是一种非常常见的模式。任何服务都不应该依赖于视图。这让我开始思考，如果我们将所有服务模块放入一个文件夹中，将所有视图模块放入另一个文件夹中，并按正确的顺序创建两个不同的目录，会怎样。经过一番挖掘，我发现了这篇文章 其中提到了称为 AggregateModuleCatalog 的东西，它用于将一堆目录连接在一起。我在此处找到了此类的源代码。以下是我使用它的方式：

class Bootstrapper : UnityBootstrapper
{
    protected override System.Windows.DependencyObject CreateShell() {...}
    protected override void InitializeShell() {...}

    protected override IModuleCatalog CreateModuleCatalog()
    {
        return new AggregateModuleCatalog();
    }

    protected override void ConfigureModuleCatalog()
    {
        ((AggregateModuleCatalog)ModuleCatalog).AddCatalog(new DirectoryModuleCatalog { ModulePath = "Modules.Services" });
        ((AggregateModuleCatalog)ModuleCatalog).AddCatalog(new DirectoryModuleCatalog { ModulePath = "Modules.Views" });
    }
}

还有 AggregateModuleCatalog：

public class AggregateModuleCatalog : IModuleCatalog
{
    private List<IModuleCatalog> catalogs = new List<IModuleCatalog>();

    /// <summary>
    /// Initializes a new instance of the <see cref="AggregateModuleCatalog"/> class.
    /// </summary>
    public AggregateModuleCatalog()
    {
        this.catalogs.Add(new ModuleCatalog());
    }

    /// <summary>
    /// Gets the collection of catalogs.
    /// </summary>
    /// <value>A read-only collection of catalogs.</value>
    public ReadOnlyCollection<IModuleCatalog> Catalogs
    {
        get
        {
            return this.catalogs.AsReadOnly();
        }
    }

    /// <summary>
    /// Adds the catalog to the list of catalogs
    /// </summary>
    /// <param name="catalog">The catalog to add.</param>
    public void AddCatalog(IModuleCatalog catalog)
    {
        if (catalog == null)
        {
            throw new ArgumentNullException("catalog");
        }

        this.catalogs.Add(catalog);
    }

    /// <summary>
    /// Gets all the <see cref="ModuleInfo"/> classes that are in the <see cref="ModuleCatalog"/>.
    /// </summary>
    /// <value></value>
    public IEnumerable<ModuleInfo> Modules
    {
        get
        {
            return this.Catalogs.SelectMany(x => x.Modules);
        }
    }

    /// <summary>
    /// Return the list of <see cref="ModuleInfo"/>s that <paramref name="moduleInfo"/> depends on.
    /// </summary>
    /// <param name="moduleInfo">The <see cref="ModuleInfo"/> to get the</param>
    /// <returns>
    /// An enumeration of <see cref="ModuleInfo"/> that <paramref name="moduleInfo"/> depends on.
    /// </returns>
    public IEnumerable<ModuleInfo> GetDependentModules(ModuleInfo moduleInfo)
    {
        var catalog = this.catalogs.Single(x => x.Modules.Contains(moduleInfo));
        return catalog.GetDependentModules(moduleInfo);
    }

    /// <summary>
    /// Returns the collection of <see cref="ModuleInfo"/>s that contain both the <see cref="ModuleInfo"/>s in
    /// <paramref name="modules"/>, but also all the modules they depend on.
    /// </summary>
    /// <param name="modules">The modules to get the dependencies for.</param>
    /// <returns>
    /// A collection of <see cref="ModuleInfo"/> that contains both all <see cref="ModuleInfo"/>s in <paramref name="modules"/>
    /// and also all the <see cref="ModuleInfo"/> they depend on.
    /// </returns>
    public IEnumerable<ModuleInfo> CompleteListWithDependencies(IEnumerable<ModuleInfo> modules)
    {
        var modulesGroupedByCatalog = modules.GroupBy<ModuleInfo, IModuleCatalog>(module => this.catalogs.Single(catalog => catalog.Modules.Contains(module)));
        return modulesGroupedByCatalog.SelectMany(x => x.Key.CompleteListWithDependencies(x));
    }

    /// <summary>
    /// Initializes the catalog, which may load and validate the modules.
    /// </summary>
    public void Initialize()
    {
        foreach (var catalog in this.Catalogs)
        {
            catalog.Initialize();
        }
    }

    /// <summary>
    /// Adds a <see cref="ModuleInfo"/> to the <see cref="ModuleCatalog"/>.
    /// </summary>
    /// <param name="moduleInfo">The <see cref="ModuleInfo"/> to add.</param>
    public void AddModule(ModuleInfo moduleInfo)
    {
        this.catalogs[0].AddModule(moduleInfo);
    }
}

我还应该提到该文章指出了以下内容：

为了演示使用 ModuleCatalog 的多种方法，
使用 Unity 的 QuickStart 实现了 AggregateModuleCatalog
源自 IModuleCatalog。该类不适合用于
运输申请。

我不确定为什么会这样。很想听到任何关于原因的解释。

Answer 7

有一个类似的问题，Fergus Bowns 的答案与 Haukinger 建议的 SmartDirectoryCatalog 相结合： Multiple DirectoryModuleCatalog in a Prism application
。我将其用于“可选依赖项”。希望这会对某人有所帮助。

PS：使用实际的 Prism Unity 7.2，您需要将 ModuleInfo 替换为 IModuleInfo