如何替换MEF容器中导出的零件/对象?

DI容器负责将所有内容连接在一起。

单元测试负责独立地测试单个代码单元。mock用于替换依赖项。因此,原则上,在单元测试中不应该使用DI容器。它与“单元测试”的定义相矛盾()

// first set up the main export provider
var mainCatalog = new AggregateCatalog(...); 
var mainExportProvider = new CatalogExportProvider(mainCatalog);

// now set up a container with mocks
var mockContainer = new CompositionContainer();
mockContainer.ComposeExportedValue<IFoo>(fooMock);
mockContainer.ComposeExportedValue<IBar>(barMock);

// use this testContainer, it will give precedence to mocks when available
var testContainer = new CompositionContainer(mockContainer, mainExportProvider);

// link back to the testContainer so mainExportProvider picks up the mocks
mainExportProvider.SourceProvider = testContainer;

() _{从你的博客来看,我相信你已经知道了。但是其他人也会读到这个答案,所以我想弄清楚“单元测试”这个词。}

无法使可接受的解决方案工作。以下代码应起作用,优先顺序在 AggregateExportProvider .

var mainContainer = new CompostionContainer();
mainContainer.ComposeExportedValue<IFoo>(new Foo() {Test = 1});

var mockContainer = new CompositionContainer();            
mockContainer.ComposeExportedValue<IFoo>(new Foo() {Test = 2});

var aggregateExportProvider = new AggregateExportProvider(
     mockContainer,   // IFoo in this container takes precedence
     mainContainer);

IFoo foo = aggregateExportProvider.GetExportedValue<IFoo>();

Console.WriteLine(foo.Test); // Outputs: 2