NullReferenceException

  • Thread starter Thread starter Joey Wu
  • Start date Start date
J

Joey Wu

Dear All.

I always got "WebException" or "NullReferenceException" errors when I try to
use internet functions.
In this case , I can get the file size and type.
Please help thanks!

======================================
Public Function picDownload(ByVal txUrl As String) As String
' Create and start an asynchronous web request
Dim req As HttpWebRequest
Dim u As New Uri(txUrl)
req = HttpWebRequest.Create(u.ToString)
req.Method = "GET"
Cursor.Current = Cursors.WaitCursor
Dim ar As IAsyncResult = req.BeginGetResponse(AddressOf
OnResponseReceived, req)
'MessageBox.Show(txUrl, "txUrl")

' Indicate that we are performing a lengthy operation
picDownload = "ok"

End Function

Private Sub OnResponseReceived(ByVal ar As IAsyncResult)
' Restore the cursor
'Cursor.Current = Cursors.Default
Me.Invoke(New EventHandler(AddressOf RestoreCursor))
' Get the web response. If connection to the web server has failed,
this is where we will get the exception
Dim rsp As WebResponse
Try
rsp = CType(ar.AsyncState, HttpWebRequest).EndGetResponse(ar)
Catch ex As WebException
MessageBox.Show(ex.ToString(), "Exception")
Exit Sub
End Try

MessageBox.Show(String.Format("Received responce. Type: {0}, Length:
{1}", rsp.ContentType, rsp.ContentLength))


Dim st As Stream = rsp.GetResponseStream()
Dim cbRead As Int32 = 0
Dim FileName As String = "temp.jpg" ' default file name in case one
was not supplied

Try

' Extract file name from Content-Disposition header
Dim hdrDisp As String = rsp.Headers.Item("Content-disposition")
Dim m As Match
For Each part As String In hdrDisp.Split(";")
m = Regex.Match(part, "filename=(.+)")
If m.Success Then
FileName = m.Groups(1).Value
Exit For
End If
Next

Dim wrt As FileStream = New FileStream("\disk\" & FileName,
FileMode.Create)
' Keep reading from the network stream until it is empty
Dim data(1024) As Byte
Do
cbRead = st.Read(data, 0, 1024)
If cbRead = 0 Then Exit Do
wrt.Write(data, 0, cbRead)
Loop
' Close the file. We are done
wrt.Close()
MessageBox.Show("File saved")

Dim MyImage As Bitmap
MyImage = New Bitmap("\disk\" & FileName)
Me.picLook.Image = CType(MyImage, Image)

Catch aax As NullReferenceException
MessageBox.Show(aax.ToString, "Exception")
End Try

End Sub
 
You are only catching WebException in your try/catch handler. Try catching
generic Exception to see if you are getting something else than
WebException. When you get an exception, please provide the complete text in
your post to help answering your question.

Also make sure that you can open the same url using pocket IE
 
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