我正在使用MEF1并进入一个奇怪的场景。
永远不会调用此构造函数：
[ImportingConstructor]
public LogViewModuleRoot(INavigationCommandManager navigationCommandManager,
ISettingsManager settingsManager,
IBusyService busyService)
{
NavigationCommandManager = navigationCommandManager;
SettingsManager = settingsManager;
BusyService = busyService;
}
在更改为此时，使用正确的值调用构造函数：
[ImportingConstructor]
public LogViewModuleRoot(INavigationCommandManager navigationCommandManager,
ISettingsManager settingsManager,
[Import(AllowDefault = true)] IBusyService busyService)
{
NavigationCommandManager = navigationCommandManager;
SettingsManager = settingsManager;
BusyService = busyService; // Properly hydrated - i.e. not null
}
通常，如果没有匹配的导出，则不会调用ImportingConstructor，但如果没有匹配的导出，则当 AllowDefault 设置为时，将无法加载是的。
哪些问题可能导致此行为？
如果这与组合图中的循环依赖关系以及构建 IBusyService 的时间有关，是否有工具可以找到问题的根源？
似乎没有深度循环依赖。即使IBusyService的导出没有自己的导入，问题仍然存在。另请注意，导出的IBusyService实例在此ImportingConstructor尝试运行之前很久就会加载。
使用MEFX Visualizer，两个案例都表明没有构图问题，并且所有导入都得到满足。
这是MEFX CompositionInfo的输出：
[Part] ****.Modularity.Logging.CallbackLogger from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Logging.CallbackLogger (ContractName="****.Modularity.Logging.CallbackLogger")
[Part] ****.Modularity.Modules.ModuleManager from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Modules.ModuleManager (ContractName="****.Modularity.Modules.IModuleManager")
[Import] ****.Modularity.Modules.ModuleManager.ImportedModules (ContractName="****.Modularity.IModule")
[SatisfiedBy] Debug.Module.ModuleRoot (ContractName="****.Modularity.IModule") from: Debug.Module.ModuleRoot from: AssemblyCatalog (Assembly="Debug.Module, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Unsuitable] Logging.Module.LogConfigurationModuleRoot (ContractName="****.Modularity.IModule") from: Logging.Module.LogConfigurationModuleRoot from: AssemblyCatalog (Assembly="Logging.Module, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Unsuitable] Logging.Module.LogViewModuleRoot (ContractName="****.Modularity.IModule") from: Logging.Module.LogViewModuleRoot from: AssemblyCatalog (Assembly="Logging.Module, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Modules.ModuleManager..ctor (Parameter="moduleCatalog", ContractName="****.Modularity.Modules.IModuleCatalog")
[SatisfiedBy] ****.Modularity.Modules.IModuleCatalog
[Import] ****.Modularity.Modules.ModuleManager..ctor (Parameter="logger", ContractName="****.Modularity.Logging.ILogger")
[SatisfiedBy] ****.Modularity.Logging.ILogger
[Import] ****.Modularity.Modules.ModuleManager..ctor (Parameter="exServiceLocator", ContractName="****.Modularity.IExtendedServiceLocator")
[SatisfiedBy] ****.Modularity.IExtendedServiceLocator
[Part] ****.Modularity.Shells.ConsoleShell from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Shells.ConsoleShell (ContractName="****.Modularity.Shells.ConsoleShell")
[Import] ****.Modularity.Shells.ConsoleShell..ctor (Parameter="navigationManager", ContractName="****.Modularity.Windows.Navigation.INavigationManager")
[SatisfiedBy] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Modularity.Windows.Navigation.INavigationManager") from: ****.Modularity.Windows.Navigation.NavigationManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.ConsoleShell..ctor (Parameter="logger", ContractName="****.Modularity.Logging.CallbackLogger")
[SatisfiedBy] ****.Modularity.Logging.CallbackLogger (ContractName="****.Modularity.Logging.CallbackLogger") from: ****.Modularity.Logging.CallbackLogger from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.ConsoleShell..ctor (Parameter="locator", ContractName="****.Modularity.IExtendedServiceLocator")
[SatisfiedBy] ****.Modularity.IExtendedServiceLocator
[Import] ****.Modularity.Shells.ConsoleShell..ctor (Parameter="viewModel", ContractName="****.Modularity.Shells.ViewModel.ShellViewModel")
[SatisfiedBy] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Shells.ViewModel.ShellViewModel") from: ****.Modularity.Shells.ViewModel.ShellViewModel from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Part] ****.Modularity.Shells.****LegacyNavigation from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Shells.****LegacyNavigation (ContractName="****.Modularity.Shells.****LegacyNavigation")
[Import] ****.Modularity.Shells.****LegacyNavigation..ctor (Parameter="navigationManager", ContractName="****.Modularity.Windows.Navigation.INavigationManager")
[SatisfiedBy] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Modularity.Windows.Navigation.INavigationManager") from: ****.Modularity.Windows.Navigation.NavigationManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.****LegacyNavigation..ctor (Parameter="logger", ContractName="****.Modularity.Logging.CallbackLogger")
[SatisfiedBy] ****.Modularity.Logging.CallbackLogger (ContractName="****.Modularity.Logging.CallbackLogger") from: ****.Modularity.Logging.CallbackLogger from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.****LegacyNavigation..ctor (Parameter="locator", ContractName="****.Modularity.IExtendedServiceLocator")
[SatisfiedBy] ****.Modularity.IExtendedServiceLocator
[Import] ****.Modularity.Shells.****LegacyNavigation..ctor (Parameter="dataContext", ContractName="****.Modularity.Windows.Shell.IShellDataContext")
[SatisfiedBy] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.Shell.IShellDataContext") from: ****.Modularity.Shells.ViewModel.ShellViewModel from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Part] ****.Modularity.Shells.KioskShell from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Shells.KioskShell (ContractName="****.Modularity.Shells.KioskShell")
[Import] ****.Modularity.Shells.KioskShell..ctor (Parameter="navigationManager", ContractName="****.Modularity.Windows.Navigation.INavigationManager")
[SatisfiedBy] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Modularity.Windows.Navigation.INavigationManager") from: ****.Modularity.Windows.Navigation.NavigationManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.KioskShell..ctor (Parameter="logger", ContractName="****.Modularity.Logging.CallbackLogger")
[SatisfiedBy] ****.Modularity.Logging.CallbackLogger (ContractName="****.Modularity.Logging.CallbackLogger") from: ****.Modularity.Logging.CallbackLogger from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.KioskShell..ctor (Parameter="dataContext", ContractName="****.Modularity.Windows.Shell.IShellDataContext")
[SatisfiedBy] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.Shell.IShellDataContext") from: ****.Modularity.Shells.ViewModel.ShellViewModel from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Part] ****.Modularity.Shells.ViewModel.ShellViewModel from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.Shell.IShellDataContext")
[Export] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.Commanding.INavigationContext")
[Export] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.IBusyService")
[Export] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Shells.ViewModel.ShellViewModel")
[Import] ****.Modularity.Shells.ViewModel.ShellViewModel..ctor (Parameter="navigationCommandManager", ContractName="****.Modularity.Windows.Commanding.INavigationCommandManager")
[SatisfiedBy] ****.Modularity.Windows.Commanding.INavigationCommandManager
[Unsuitable] ****.Modularity.Windows.Commanding.NavigationCommandManager (ContractName="****.Modularity.Windows.Commanding.INavigationCommandManager") from: ****.Modularity.Windows.Commanding.NavigationCommandManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.ViewModel.ShellViewModel..ctor (Parameter="menuCommandManager", ContractName="****.Modularity.Windows.IMenuCommandManager")
[SatisfiedBy] ****.Modularity.Windows.Commanding.MenuCommandManager (ContractName="****.Modularity.Windows.IMenuCommandManager") from: ****.Modularity.Windows.Commanding.MenuCommandManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.ViewModel.ShellViewModel..ctor (Parameter="applicationInformation", ContractName="****.Modularity.Shells.IApplicationInformation")
[SatisfiedBy] ****.Modularity.Shells.IApplicationInformation
[Import] ****.Modularity.Shells.ViewModel.ShellViewModel..ctor (Parameter="manager", ContractName="****.Modularity.Modules.IModuleManager")
[SatisfiedBy] ****.Modularity.Modules.ModuleManager (ContractName="****.Modularity.Modules.IModuleManager") from: ****.Modularity.Modules.ModuleManager from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Shells.ViewModel.ShellViewModel..ctor (Parameter="actionExecuter", ContractName="****.Modularity.IActionExecuter")
[SatisfiedBy] ****.Modularity.IActionExecuter
[Part] ****.Modularity.Windows.Commanding.MenuCommandManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Windows.Commanding.MenuCommandManager (ContractName="****.Modularity.Windows.IMenuCommandManager")
[Import] ****.Modularity.Windows.Commanding.MenuCommandManager..ctor (Parameter="moduleManager", ContractName="****.Modularity.Modules.IModuleManager")
[SatisfiedBy] ****.Modularity.Modules.ModuleManager (ContractName="****.Modularity.Modules.IModuleManager") from: ****.Modularity.Modules.ModuleManager from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Windows.Commanding.MenuCommandManager..ctor (Parameter="navigationManager", ContractName="****.Modularity.Windows.Navigation.INavigationManager")
[SatisfiedBy] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Modularity.Windows.Navigation.INavigationManager") from: ****.Modularity.Windows.Navigation.NavigationManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Part] ****.Modularity.Windows.Commanding.NavigationCommandManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Windows.Commanding.NavigationCommandManager (ContractName="****.Modularity.Windows.Commanding.INavigationCommandManager")
[Import] ****.Modularity.Windows.Commanding.NavigationCommandManager..ctor (Parameter="moduleManager", ContractName="****.Modularity.Modules.IModuleManager")
[SatisfiedBy] ****.Modularity.Modules.ModuleManager (ContractName="****.Modularity.Modules.IModuleManager") from: ****.Modularity.Modules.ModuleManager from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Windows.Commanding.NavigationCommandManager..ctor (Parameter="navigationManager", ContractName="****.Modularity.Windows.Navigation.INavigationManager")
[SatisfiedBy] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Modularity.Windows.Navigation.INavigationManager") from: ****.Modularity.Windows.Navigation.NavigationManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Part] ****.Modularity.Windows.Commanding.MenuNavigationCommandManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Windows.Commanding.MenuNavigationCommandManager (ContractName="****.Modularity.Windows.Commanding.MenuNavigationCommandManager")
[Import] ****.Modularity.Windows.Commanding.MenuNavigationCommandManager..ctor (Parameter="moduleManager", ContractName="****.Modularity.Modules.IModuleManager")
[SatisfiedBy] ****.Modularity.Modules.ModuleManager (ContractName="****.Modularity.Modules.IModuleManager") from: ****.Modularity.Modules.ModuleManager from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Windows.Commanding.MenuNavigationCommandManager..ctor (Parameter="navigationManager", ContractName="****.Modularity.Windows.Navigation.INavigationManager")
[SatisfiedBy] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Modularity.Windows.Navigation.INavigationManager") from: ****.Modularity.Windows.Navigation.NavigationManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] ****.Modularity.Windows.Commanding.MenuNavigationCommandManager..ctor (Parameter="menuCommandManager", ContractName="****.Modularity.Windows.IMenuCommandManager")
[SatisfiedBy] ****.Modularity.Windows.Commanding.MenuCommandManager (ContractName="****.Modularity.Windows.IMenuCommandManager") from: ****.Modularity.Windows.Commanding.MenuCommandManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Part] ****.Modularity.Windows.Navigation.NavigationManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Export] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Framework.ViewModel.INavigationService")
[Export] ****.Modularity.Windows.Navigation.NavigationManager (ContractName="****.Modularity.Windows.Navigation.INavigationManager")
[Import] ****.Modularity.Windows.Navigation.NavigationManager..ctor (Parameter="moduleManager", ContractName="****.Modularity.Modules.IModuleManager")
[SatisfiedBy] ****.Modularity.Modules.ModuleManager (ContractName="****.Modularity.Modules.IModuleManager") from: ****.Modularity.Modules.ModuleManager from: AssemblyCatalog (Assembly="****.Modularity.Mef, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Part] Logging.Module.LogConfigurationModuleRoot from: AssemblyCatalog (Assembly="Logging.Module, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] Logging.Module.LogConfigurationModuleRoot (ContractName="****.Modularity.IModule")
[Import] Logging.Module.LogConfigurationModuleRoot..ctor (Parameter="logConfiguration", ContractName="Logging.ViewModel.Interfaces.ILogConfiguration")
[SatisfiedBy] Logging.ViewModel.LogConfigurationViewModel (ContractName="Logging.ViewModel.Interfaces.ILogConfiguration") from: Logging.ViewModel.LogConfigurationViewModel from: AssemblyCatalog (Assembly="Logging.ViewModel, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Part] Logging.Module.LogViewModuleRoot from: AssemblyCatalog (Assembly="Logging.Module, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] Logging.Module.LogViewModuleRoot (ContractName="****.Modularity.IModule")
[Import] Logging.Module.LogViewModuleRoot..ctor (Parameter="navigationCommandManager", ContractName="****.Modularity.Windows.Commanding.INavigationCommandManager")
[SatisfiedBy] ****.Modularity.Windows.Commanding.INavigationCommandManager
[Unsuitable] ****.Modularity.Windows.Commanding.NavigationCommandManager (ContractName="****.Modularity.Windows.Commanding.INavigationCommandManager") from: ****.Modularity.Windows.Commanding.NavigationCommandManager from: AssemblyCatalog (Assembly="****.Modularity.Windows, Version=2.4.0.347, Culture=neutral, PublicKeyToken=null")
[Import] Logging.Module.LogViewModuleRoot..ctor (Parameter="settingsManager", ContractName="****.Modularity.ISettingsManager")
[SatisfiedBy] ****.Modularity.ISettingsManager
[Import] Logging.Module.LogViewModuleRoot..ctor (Parameter="busyService", ContractName="****.Modularity.Windows.IBusyService")
[SatisfiedBy] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.IBusyService") from: ****.Modularity.Shells.ViewModel.ShellViewModel from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Part] Logging.ViewModel.LogConfigurationViewModel from: AssemblyCatalog (Assembly="Logging.ViewModel, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] Logging.ViewModel.LogConfigurationViewModel (ContractName="Logging.ViewModel.Interfaces.ILogConfiguration")
[Import] Logging.ViewModel.LogConfigurationViewModel..ctor (Parameter="viewModelManager", ContractName="****.Framework.ViewModel.ViewModelManager")
[SatisfiedBy] ****.Framework.ViewModel.ViewModelManager
[Import] Logging.ViewModel.LogConfigurationViewModel..ctor (Parameter="settingsManager", ContractName="****.Modularity.ISettingsManager")
[SatisfiedBy] ****.Modularity.ISettingsManager
[Import] Logging.ViewModel.LogConfigurationViewModel..ctor (Parameter="busyService", ContractName="****.Modularity.Windows.IBusyService")
[SatisfiedBy] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.IBusyService") from: ****.Modularity.Shells.ViewModel.ShellViewModel from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Import] Logging.ViewModel.LogConfigurationViewModel..ctor (Parameter="actionExecuter", ContractName="****.Modularity.IActionExecuter")
[SatisfiedBy] ****.Modularity.IActionExecuter
[Part] Debug.Module.ModuleRoot from: AssemblyCatalog (Assembly="Debug.Module, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Export] Debug.Module.ModuleRoot (ContractName="****.Modularity.IModule")
[Import] Debug.Module.ModuleRoot..ctor (Parameter="container", ContractName="System.ComponentModel.Composition.Hosting.CompositionContainer")
[SatisfiedBy] System.ComponentModel.Composition.Hosting.CompositionContainer
[Import] Debug.Module.ModuleRoot..ctor (Parameter="catalogs", ContractName="System.ComponentModel.Composition.Primitives.ComposablePartCatalog")
[SatisfiedBy] System.ComponentModel.Composition.Primitives.ComposablePartCatalog
[Import] Debug.Module.ModuleRoot..ctor (Parameter="shell", ContractName="****.Modularity.Windows.Shell.IShellDataContext")
[SatisfiedBy] ****.Modularity.Shells.ViewModel.ShellViewModel (ContractName="****.Modularity.Windows.Shell.IShellDataContext") from: ****.Modularity.Shells.ViewModel.ShellViewModel from: AssemblyCatalog (Assembly="****.Modularity.Shells, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
[Import] Debug.Module.ModuleRoot..ctor (Parameter="settingsManager", ContractName="****.Modularity.ISettingsManager")
[SatisfiedBy] ****.Modularity.ISettingsManager
答案 0 :(得分：2)
由于ShellViewModel导出IBusyService和LogViewModuleRoot导入IBusyService
您确实有一个预导出（即构造函数导入）周期：
ShellViewModel - ＆gt; IModuleManager - ＆gt; IModule（s） - ＆gt; LogViewModuleRoot
AllowDefault = true允许该循环中断，并且它不为null的原因是由于这些循环的构造顺序。它不是确定性的，如果你首先拉动LogViewModuleRoot对象，在另一种情况下很可能是null。
打破循环并确保始终设置的最佳方法可能是将IBusyService切换到LogViewModuleRoot上的属性导入。