.NET 中如何定义泛型接口统一不同入参的GetOpenPositions方法签名

你之前实现报错的原因是C#接口实现要求参数签名完全一致，接口约定的入参是IEnumerable<OpenPositionBase>，实现类直接替换为子类集合类型属于类型不匹配，通过给接口加泛型约束就能完美解决：

// 定义带泛型约束的接口，T必须继承自公共基类OpenPositionBase
public interface IPositionConverter<T> where T : OpenPositionBase
{
    IEnumerable<Position> GetOpenPositions(IEnumerable<T> openPositions, uint ownerId, IEnumerable<agile_shared.RequestModel.OpenPosition> orgOpenPositionList);
}

实现类只要指定对应的泛型参数即可，不需要修改原有业务逻辑：

public class AlliancePositionConverter : IPositionConverter<AllianceOpenPosition>
{
    public IEnumerable<Position> GetOpenPositions(IEnumerable<AllianceOpenPosition> allianceOpenPositions, uint allianceId, IEnumerable<agile_shared.RequestModel.OpenPosition> orgOpenPositionList)
    {
        return allianceOpenPositions.Where(w => w.AllianceId == allianceId)
                                    .Select(s => new Position(orgOpenPositionList.FirstOrDefault(wh => wh.Id == s.OpenPositionId))
                                    {
                                        Id = s.Id.ToString(),
                                        AgileRole = s.LeadRole.Name,
                                        AgileRoleRank=s.LeadRole.Rank
                                    }).ToList();
    }
}

同理其他两个实现类只需要把泛型参数替换为SquadOpenPosition、TribeOpenPosition即可，后续如果新增其他继承自OpenPositionBase的类型，只要新增对应实现类指定泛型参数就行，扩展性极强。 #

如果有统一调度所有Converter的需求，还可以搭配泛型协变实现多态调用：

// 给泛型参数加out关键字开启协变
public interface IPositionConverter<out T> where T : OpenPositionBase
{
    IEnumerable<Position> GetOpenPositions(IEnumerable<OpenPositionBase> openPositions, uint ownerId, IEnumerable<agile_shared.RequestModel.OpenPosition> orgOpenPositionList);
}

// 实现类内部做类型安全转换
public class AlliancePositionConverter : IPositionConverter<AllianceOpenPosition>
{
    public IEnumerable<Position> GetOpenPositions(IEnumerable<OpenPositionBase> openPositions, uint allianceId, IEnumerable<agile_shared.RequestModel.OpenPosition> orgOpenPositionList)
    {
        var allianceOpenPositions = openPositions.OfType<AllianceOpenPosition>();
        return allianceOpenPositions.Where(w => w.AllianceId == allianceId)
                                    .Select(s => new Position(orgOpenPositionList.FirstOrDefault(wh => wh.Id == s.OpenPositionId))
                                    {
                                        Id = s.Id.ToString(),
                                        AgileRole = s.LeadRole.Name,
                                        AgileRoleRank=s.LeadRole.Rank
                                    }).ToList();
    }
}

这种方案下你可以把所有Converter存入List<IPositionConverter<OpenPositionBase>>集合，实现动态匹配调用的需求。

内容的提问来源于stack exchange，提问作者Sándor Jankovics