为什么我得到：'System.Collections.IEnumerable' 没有类型参数，因此不能有类型参数？

Question

这是我的简单用户名和密码登录，它能够将用户重定向到不同的“会员区”页面。

但是我得到一个：

BC32045：“System.Collections.IEnumerable”没有类型参数，因此不能有类型参数

我也不知道为什么。

有人可以帮忙吗？

谢谢，大卫。

Public Class MyPage
Inherits Page
Private Structure Cred
    Public Username As String
    Public Password As String
    Public RedirectUrl As String
    Public Sub New(un As String, pw As String, Optional ru As String = "/admin/default.aspx")
        Username = un
        Password = pw
        RedirectUrl = ru
    End Sub
End Structure

Private ReadOnly _credentials As IEnumerable(Of Cred) = New () {New Cred("userone", "passwordone"), New Cred("usertwo", "passwordtwo"), New Cred("userthree", "passwordthree", "/admin/custom.aspx")}

Public Sub Page_Load(sender As Object, e As EventArgs)
    Dim user = _credentials.SingleOrDefault(Function(x) x.Username = UserName.Text AndAlso x.Password = Password.Text)
    If user IsNot Nothing Then
        Session("Admin") = True
        Response.Redirect(user.RedirectUrl)
    Else
        Session("Admin") = False
        LtlLogin.Text = "<p>Sorry, you have provided incorrect login details.</p>"
    End If
End Sub
End Class

Answer 1

我得到正确的“类型预期”编译器错误。要么删除New()，所以替换

Private ReadOnly _credentials As IEnumerable(Of Cred) = New () {New Cred("userone", "passwordone"), New Cred("usertwo", "passwordtwo"), New Cred("userthree", "passwordthree", "/admin/custom.aspx")}

与

Private ReadOnly _credentials As IEnumerable(Of Cred) =  {New Cred("userone", "passwordone"), New Cred("usertwo", "passwordtwo"), New Cred("userthree", "passwordthree", "/admin/custom.aspx")}

或使用New Cred(){...}

但是，您应该使用类而不是结构。对于Option Strict，您不能使用If user IsNot Nothing，因为Cred 是Structure，因此是值类型。