Question

我有很多具有BeginDate和EndDate属性的类，我想构建一个泛型方法，将一个对象作为相同类型的List返回，但使用BeginDate=EndDate。

前：

Item.BeginDate = 2011-05-01， Item.EndDate = 2011-05-03

结果必须是

Item1.BeginDate = 2011-05-01，   Item1.EndDate = 2011-05-01

Item2.BeginDate = 2011-05-02，   Item2.EndDate = 2011-05-02

Item3.BeginDate = 2011-05-03，   Item3.EndDate = 2011-05-03

我尝试了以下代码

<Extension()> _
        Public Function GetRatesPerDay(Of T As Class)(ByVal oldRatesList As List(Of T)) As List(Of T)
            If oldRatesList Is Nothing OrElse oldRatesList.Count = 0 Then
                Return New List(Of T)
            End If
            Dim ratesInDays As New List(Of T)

            Dim oldBeginDate = oldRatesList.Where(Function(D) D IsNot Nothing).Min(Function(D) GetType(T).GetProperty("BeginDate", GetType(DateTime)).GetValue(D, Nothing))
            Dim oldEndDate = oldRatesList.Where(Function(D) D IsNot Nothing).Max(Function(D) GetType(T).GetProperty("EndDate", GetType(DateTime)).GetValue(D, Nothing))

            Dim currentDay As DateTime = oldBeginDate

            Dim typeArgs() As Type = {GetType(DateTime), GetType(DateTime), GetType(Nullable(Of Double)), GetType(String), GetType(HUMPSBaseClasses.RoomRateType)}
            Dim constructed As Type = GetType(T).MakeGenericType(typeArgs)

            While currentDay <= oldEndDate
                Dim dayRate = (From D In oldRatesList _
                                Where D IsNot Nothing _
                                AndAlso currentDay >= GetType(T).GetProperty("BeginDate", GetType(DateTime)).GetValue(D, Nothing) _
                                AndAlso currentDay <= GetType(T).GetProperty("EndDate", GetType(DateTime)).GetValue(D, Nothing) _
                                Select New With {.NightRate = GetType(T).GetProperty("NightRate", GetType(Nullable(Of Double))).GetValue(D, Nothing), _
                                                 .RatePlanID = GetType(T).GetProperty("RatePlanID", GetType(System.String)).GetValue(D, Nothing), _
                                                 .RoomRateType = GetType(T).GetProperty("RoomRateType", GetType(HUMPSBaseClasses.RoomRateType)).GetValue(D, Nothing) _
                                                 }).SingleOrDefault()

                If dayRate IsNot Nothing Then
                    Dim tempRate As Object = Activator.CreateInstance(constructed)
                    tempRate = New With {.BeginDate = currentDay, _
                                             .EndDate = currentDay, _
                                             .NightRate = dayRate.NightRate, _
                                             .RatePlanID = dayRate.RatePlanID, _
                                             .RoomRateType = dayRate.RoomRateType}
                    ratesInDays.Add(tempRate)
                End If
                currentDay = currentDay.AddDays(1)
            End While
            Return ratesInDays
        End Function

但是我遇到了Type.IsGenericTypeDefinition我班级错误的问题。

如何将其设置为true？

Answer 1

你做不到。这是一个只读属性。

你得到false，因为这个类不是通用的。只有你的方法。

您应该能够反思类型并检索MethodInfo。然后，您可以使用MethodInfo.IsGenericMethod或MethodInfo.IsGenericMethodDefinition。

你的另一个选择是将类修改为通用类，但这样就太过分了，因为这是（我猜这里）唯一需要泛型参数的方法。

Answer 2

您无法设置此属性的值 - 它是只读的。

如何将Type.IsGenericTypeDefinition设置为true？

2 个答案: