错误：“无法将类型为'X'的对象强制转换为类型'X'"

本文介绍了错误：“无法将类型为'X'的对象强制转换为类型'X'"的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 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 = 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），companypanyid）+'）'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 panyid = companypanyid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), companypanyid) + ')' 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 offerpanyid = companypanyid 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