asp.net 自定义错误页面不起作用

Question

我在 IIS8.5 上有一个自定义错误页面。有时错误页面本身会抛出异常:

Object reference not set to an instance of an object.

这是我背后的代码的一部分:

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        HttpContext.Current.Response.StatusCode = 500
        'Dim CurrentException As Exception = Server.GetLastError()
        'virheettxt.text = CurrentException.Message
        Dim hostName = System.Net.Dns.GetHostName()



        Dim ctxOBJ As HttpContext
        Dim exceptionOBJ As Exception
        Dim errorInfoTXT As String

        ctxOBJ = HttpContext.Current()

        exceptionOBJ = ctxOBJ.Server.GetLastError()

        errorInfoTXT = " <br>Offending URL: " & iif(Not ctxOBJ Is Nothing, ctxOBJ.Request.Url.ToString(), "ei saatavilla") &
"<br>Source: " & iif(Not exceptionOBJ Is Nothing, exceptionOBJ.Source.ToString(), "ei saatavilla") &
"<br>Message: " & iif(Not exceptionOBJ Is Nothing, exceptionOBJ.Message.ToString(), "ei saatavilla") &
"<br>Stack trace: " & iif(Not exceptionOBJ Is Nothing, exceptionOBJ.StackTrace.ToString(), "ei saatavilla") &
"<br>Target Site: " & iif(Not exceptionOBJ Is Nothing, exceptionOBJ.TargetSite.ToString(), "ei saatavilla") &
"<br>Server: " & hostName
        Dim virheurlsc = ctxOBJ.Request.Url.ToString()



        ctxOBJ.Server.ClearError()

错误来自行:errorInfoTXT = "违规网址:......

如果有一种方法可以捕获错误行，我在某些情况下也确实需要它......？

Answer 1

问题来自于使用 Iif ，它评估真实和错误的情况。使用 If() operator相反会阻止这种情况。

您还应该检查是否 ctxOBJ在尝试使用它之前什么都不是，如果你颠倒 If()s 中的 true 和 false 参数，它会让它更简单一点:

Dim ctxOBJ As HttpContext = HttpContext.Current()
Dim exceptionOBJ As Exception = Nothing

If ctxOBJ IsNot Nothing Then
    exceptionOBJ = ctxOBJ.Server.GetLastError()
End If

Dim errorInfoTXT As String = " <br>Offending URL: " & If(ctxOBJ Is Nothing, "ei saatavilla", ctxOBJ.Request.Url.ToString()) &
"<br>Source: " & If(exceptionOBJ Is Nothing, "ei saatavilla", exceptionOBJ.Source.ToString()) &
"<br>Message: " & If(exceptionOBJ Is Nothing, "ei saatavilla", exceptionOBJ.Message.ToString()) &
"<br>Stack trace: " & If(exceptionOBJ Is Nothing, "ei saatavilla", exceptionOBJ.StackTrace.ToString()) &
"<br>Target Site: " & If(exceptionOBJ Is Nothing, "ei saatavilla", exceptionOBJ.TargetSite.ToString()) &
"<br>Server: " & hostName