错误：“无法将类型为'X'的对象强制转换为类型'X'" [英] Error :"Unable to cast object of type 'X' to type 'X' "

问题描述

 受保护的  Sub  Page_Load（ ByVal 发​​件人作为 对象， ByVal  e  As  System.EventArgs）
 如果 不 IsPostBack 然后 
 如果 Request.IsAuthenticated 然后 
  Dim  ident  As  FormsIdentity = < span class =code-keyword> CType （User.Identity，FormsIdentity）
 如果 ident  IsNot   Nothing  然后 
  Dim  ticket  As  FormsAuthenticationTicket = ident.Ticket 
  Dim  userDataString  As   String  = ticket.UserData 
  Dim  userDataPieces（） As   String  = userDataString.Split（  | .ToCharArray（））
  Dim 用户名作为 字符串 = userDataPieces（ 1 ）
  Dim  rolename  As   String  = userDataPieces（  2 ）
 如果 rolename<>  研究生 然后 
 Response.Redirect（ 〜/ login.aspx，错误）
 结束 如果 
 结束 如果 
 其他 
 Response.Redirect （ 〜/ login.aspx， False ）
 结束 如果 
 lblerror.Visible =  False  
  Dim  ident1  As  FormsIdentity =  CType （User.Identity，FormsIdentity）
  Dim  ticket1  As  FormsAuthenticationTicket = ident1.Ticket 
  Dim  userDataString1  As  字符串 = ticket1.UserData 
  Dim  userDataPieces1（）作为 字符串 = userDataString1.Split（  | .ToCharArray （））
  Dim  userid  As   Integer  = userDataPieces1（ 0 ）
  Dim  ds  As  DataSet 
 
 sqlquery（ 选择offer.offerid作为'Offer ID'，companyname +'（'+ convert（varchar（50），company.companyid）+'）'作为'Company'，request.requestid作为'Request ID'， fname +''+ lname为'Student'，days为'Days'，minsalary为'Minimum Salary'，maxsalary为'Maximum Salary'，来自公司，offer，request，requestdetail，users for offer.offerid = requestdetail.offerid and offer .companyid = company.companyid和offer.userid ='&用户ID和 '和request.userid = users.userid and request.requestid = requestdetail.requestid;）
 如果 ds.Tables（ 0 ）。Rows.Count<>  0  然后 
 gvrequestgrad.DataSource = ds.Tables（ 0 ）
 gvrequestgrad.DataBind（）
 gvrequestgrad.SelectedIndex = -1 
 结束 如果 

此代码在编译错误时给出错误：

  - 无法将System.Security.Principal.WindowsIdentity类型的对象强制转换为System.Web.Security.FormsIdentity。 
 
  - 描述：执行当前Web请求期间发生未处理的异常。请查看堆栈跟踪以获取有关错误及其源自代码的位置的更多信息。 
 
 -Exception Details zh_cn：System.InvalidCastException：无法将类型为System.Security.Principal.WindowsIdentity的对象强制转换为'System.Web.Security.FormsIdentity'。

PLZ任何人都可以帮助我吗？



代码块添加，紧急删除 - OriginalGriff [/ edit]

解决方案

这一行：

  Dim  ident  As  FormsIdentity =  CType （User.Identity， FormsIdentity）

更改为：

  Dim  ident  As  IPrincipal =  CType （User.Identity，IPrincipal）

FormsIdentity无法从WindowsPrincipal进行转换/转换

哦，我现在试试吧谢谢jlopez788

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
        If Not IsPostBack Then
            If Request.IsAuthenticated Then
                Dim ident As FormsIdentity = CType(User.Identity, FormsIdentity)
                If ident IsNot Nothing Then
                    Dim ticket As FormsAuthenticationTicket = ident.Ticket
                    Dim userDataString As String = ticket.UserData
                    Dim userDataPieces() As String = userDataString.Split("|".ToCharArray())
                    Dim username As String = userDataPieces(1)
                    Dim rolename As String = userDataPieces(2)
                    If rolename <> "Graduate" Then
                        Response.Redirect("~/login.aspx", False)
                    End If
                End If
            Else
                Response.Redirect("~/login.aspx", False)
            End If
            lblerror.Visible = False
            Dim ident1 As FormsIdentity = CType(User.Identity, FormsIdentity)
            Dim ticket1 As FormsAuthenticationTicket = ident1.Ticket
            Dim userDataString1 As String = ticket1.UserData
            Dim userDataPieces1() As String = userDataString1.Split("|".ToCharArray())
            Dim userid As Integer = userDataPieces1(0)
            Dim ds As DataSet

            sqlquery("select offer.offerid as 'Offer ID', companyname + '(' + convert(varchar(50), company.companyid) + ')' as 'Company', request.requestid as 'Request ID', fname + ' ' + lname as 'Student', days as 'Days', minsalary as 'Minimum Salary', maxsalary as 'Maximum Salary' from company, offer, request, requestdetail, users where offer.offerid = requestdetail.offerid and offer.companyid = company.companyid and offer.userid = '" & userid & "' and request.userid = users.userid and request.requestid = requestdetail.requestid;")
            If ds.Tables(0).Rows.Count <> 0 Then
                gvrequestgrad.DataSource = ds.Tables(0)
                gvrequestgrad.DataBind()
                gvrequestgrad.SelectedIndex = -1
            End If 

this code is giving me an error while compiling the error is :

-Unable to cast object of type 'System.Security.Principal.WindowsIdentity' to type 'System.Web.Security.FormsIdentity'.

- Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

-Exception Details: System.InvalidCastException: Unable to cast object of type 'System.Security.Principal.WindowsIdentity' to type 'System.Web.Security.FormsIdentity'.

plz can anyone help me ?

[edit]Code block added, Urgency deleted - OriginalGriff[/edit]

解决方案

This line:

Dim ident As FormsIdentity = CType(User.Identity, FormsIdentity)

Change to:

Dim ident As IPrincipal = CType(User.Identity, IPrincipal)

FormsIdentity cannot be casted / converted from WindowsPrincipal

oh i will try it now thank you jlopez788

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