c# - 用于开放通用的 Automapper 自定义转换器

Question

映射open generics在 Automapper 中是可能的，但是我在尝试将它与自定义类型转换器结合时遇到了一些问题。

以下内容

cfg.CreateMap(typeof(IEnumerable<>), typeof(MyCustomCollectionType<>))
.ConvertUsing(typeof(MyConverter));

MyConverter 看起来像这样:

class MyConverter : ITypeConverter<object, object>
{
    public object Convert(object source, object destination, ResolutionContext context)
    {
        //... do conversion
    }
}

在创建映射时只抛出一个异常:

'System.InvalidOperationException' in mscorlib.dll

Additional information: This operation is only valid on generic types.

如何为开放通用类型定义自定义类型转换器？我需要实现什么接口(interface)？

Answer 1

开放泛型的转换器需要是泛型类型。它看起来像:

public class MyConverter<TSource, TDest> 
    : ITypeConverter<IEnumerable<TSource>, MyCustomCollectionType<TDest>> {
    public MyCustomCollectionType<TDest> Convert(
        IEnumerable<TSource> source, 
        MyCustomCollectionType<TDest> dest, 
        ResolutionContext context) {
        // you now have the known types of TSource and TDest
        // you're probably creating the dest collection
        dest = dest ?? new MyCustomCollectionType<TDest>();
        // You're probably mapping the contents
        foreach (var sourceItem in source) {
            dest.Add(context.Mapper.Map<TSource, TDest>(sourceItem));
        }
        //then returning that collection
        return dest;
    }
}