Question

我想创建一个GetAllContacts方法，它接受类型为Func（Of Contact，TKey）的排序参数，该类型与IEnumerable（Of Contact）的OrderBy方法相同。这是我的代码：

    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，SortDirection.Ascending）时，我收到错误：

"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（网络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

和此：

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

这是一个错误的错误消息。我在界面中的签名与实现中的签名不同。一旦我修复了签名，错误就消失了。

将Func（Of TElement，TKey）作为函数参数传递

2 个答案: