如何在 MEF 中使用依赖注入？

Question

我有一个 ASP.Net Core 3.1 应用程序，并且我有许多通过 MEF 加载的 plugins。简化的界面如下所示：

public interface IImportPlugin
{
    string Name { get; }
    string Category { get; }
    string Title { get; }
    string Description { get; }
}

插件类可能如下所示：

[Export(typeof(IImportPlugin))]
public sealed class ImportCustomers : IImportPlugin
{
    private ICustomerService customerService;
    //Other services...

    [ImportingConstructor]
    public ImportCustomers()
        : base()
    { 
        //Set properties
    }
}

如何将服务实例注入插件？

Answer 1

作为对您问题的回答，您有两个解决方案，分别是使用导入属性或 GetExports 方法。

对于导入（按构造函数导入）：

[Export(typeof(IImportPlugin))]
public sealed class ImportCustomers : IImportPlugin
{
    private ICustomerService _customerService;
    //Other services...

    [ImportingConstructor]
    public ImportCustomers([Import(typeof(ICustomerService))] ICustomerService customerService)
      : base()
    { 
        //Set properties
        _customerService  = customerService ;
    }
}

对于 GetExports：

[Export(typeof(IImportPlugin))]
public sealed class ImportCustomers : IImportPlugin
{
    private ICustomerService _customerService;
    //Other services...

    [ImportingConstructor]
    public ImportCustomers()
      : base()
    { 
        //You need to use your composition container
        //to resolve your instance using ICustomerService interface
        _customerService  = Container.GetExports<ICustomerService>()
                                     .Single().Value;
    }
}