Question

我要制作一种 GetAllContacts 方法, 使用Func( 联系人) 类型参数的排序参数, 与 IEO numberable( 联系人) 的排序方法相同。这里的代码 :

    Public Function GetAllContacts(Of TKey)(ByVal sort As Func(Of Contact, TKey), ByVal sortDirection As SortDirection) As IEnumerable(Of Contact) Implements IContactRepository.GetAllContacts
        Select Case sortDirection
            Case sortDirection.Ascending
                Return ContactList.OrderBy(sort)
            Case sortDirection.Descending
                Return ContactList.OrderByDescending(sort)
        End Select
    End Function

当我调用 GetAllContacts( Func( c) c. ContactID, Sort Directction. Asscating) 时,我就会发现错误 :

"Value of type  System.Func(Of Contact, String)  cannot be converted to  Integer ." on the first parameter

和

"Too many arguments to extension method  Public Function ElementAtOrDefault(index As Integer) As Contact  defined in  System.Linq.Enumerable ." on the second parameter.

我错过了什么?

Answer 1

我试过这个(净额4.0):

Public Function tst(a As String) As Integer
        Return a.Length
    End Function

    Public Function GetAllContacts(Of TKey)(ByVal sort As Func(Of String, TKey), ByVal sortDirection As DirectoryServices.SortDirection) As IEnumerable(Of String)
        Return {"a"}
    End Function

并且这一点:

GetAllContacts(AddressOf tst, DirectoryServices.SortDirection.Ascending)
GetAllContacts(Function(a As String) As Integer
                       Return a.Length
                   End Function, DirectoryServices.SortDirection.Ascending)
GetAllContacts(Function(a) a.Length, DirectoryServices.SortDirection.Ascending)

我没有错误

Answer 2

这是一个错误信息错误错误的事例。我在接口上有一个与执行不同的签名。一旦我固定了签名, 错误就消失了。

友情链接