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如何使用重写的方法参数

generics c#

Ross Bush · 技术社区 · 7 年前

BusinessClass 以接口作为强制方式的后代 Fetch_Data .

BusinessBase 会实现它自己的 获取数据 通过重写。我已经让它大部分工作了,但是,您不能使用从虚拟版本中使用的类中降序的参数重写方法,方法签名不同,编译器将不允许它。

public class BusinessLayerBaseNoCSLA<T>
{
    public virtual void Fetch_Data(BaseParameters parameters){ throw new NotWellConfiguredException();
}

扩展BusinessLayerBase:

public class Vehicle : BusinessLayerBaseNoCSLA<Vehicle>
{
    public int VehicleId { get; set; }

    public override void Fetch_Data(GetVehicleParameters parameters)//<--This line has a red squiggly because of the signature difference, no suitable method found to override.
    {
        //I could cast like  var p = (GetVehicleParameters)BaseParameters; here but something smells bad about that  
        GetVehicleParameters p = parameters;
        ... 
        VehicleId = p.VehicleId;
    }
}

DataPortal Fetch

public static class DataPortal
{
    public static T FetchData<T>(object criteria) where T : BusinessLayerBaseNoCSLA<T>, new()
    {
        var result = new T();
        result.Fetch_Data((BaseParameters)criteria);
        return result;
    }
}

var Vehicle = DataPortal.FetchData<Vehicle>(new GetVehicleParameters({ VehicleId =1 });

0 回复 | 直到 7 年前

Steve Wong 7 年前

如果您希望将特定类型的参数 Fetch_Data(BaseParameters parameters) 方法,可以将获取参数作为泛型类型引入基类。

public class BusinessLayerBaseNoCSLA<TObject, TParameters>
    where TObject : BusinessLayerBaseNoCSLA<TObject, TParameters> // optional
    where TParameters : BaseParameters
{
    public virtual void Fetch_Data(TParameters parameters)
    {
        throw new NotWellConfiguredException();
    }
}

车辆定义如下:

public class Vehicle : BusinessLayerBaseNoCSLA<Vehicle, GetVehicleParameters>
{
    public int VehicleId { get; set; }

    public override void Fetch_Data(GetVehicleParameters parameters)
    {
        //I could cast like  var p = (GetVehicleParameters)BaseParameters; here but something smells bad about that  
        // Note: No need to cast 'parameters' here!
        GetVehicleParameters p = parameters;            
        VehicleId = p.VehicleId;
    }
}

public static class DataPortal
{
    public static TObject FetchData<TObject, TParameters>(TParameters criteria) 
        where TObject : BusinessLayerBaseNoCSLA<TObject, TParameters>, new()
        where TParameters : BaseParameters
    {
        var result = new TObject();
        //result.Fetch_Data((BaseParameters)criteria);
        // Note: no need to cast criteria!
        result.Fetch_Data(criteria);
        return result;
    }
}

用法:

Vehicle vehicle = DataPortal.FetchData<Vehicle, GetVehicleParameters>(new GetVehicleParameters() { VehicleId = 1 });
// Note: we need to explicitly call the FetchData<,> with the correct types

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