nullreferenceexception未处理?对象引用未设置为对象的实例

时间:2013-08-02 06:57:28

标签: vb.net

我使用带有vb.net代码的ISBN号从亚马逊网站平行获取数据..

它只处理一些ISBN号..

当我们使用其他ISBN编号时。它会显示以下错误:

nullreferenceexception未处理。对象引用未设置为对象的实例。

如何解决这个问题? 任何人帮助..

以下是代码:

此代码中有错误吗? 任何人都给出解决方案..

Private Sub ButtonProductAdvertisingAPIItemLookup_Click(ByVal sender As System.Object,ByVal e As System.EventArgs)Handles ButtonProductAdvertisingAPIItemLookup.Click         sender.Enabled = False

    'Product Advertising API, ItemLookup: http://docs.aws.amazon.com/AWSECommerceService/2011-08-01/DG/ItemLookup.html

    Dim ItemId(9) As String

    ItemId(0) = System.Uri.EscapeDataString(TextBoxisbn1.Text)
    ItemId(1) = System.Uri.EscapeDataString(TextBoxisbn2.Text)
    ItemId(2) = System.Uri.EscapeDataString(TextBoxisbn3.Text)
    ItemId(3) = System.Uri.EscapeDataString(TextBoxisbn4.Text)
    ItemId(4) = System.Uri.EscapeDataString(TextBoxisbn5.Text)
    ItemId(5) = System.Uri.EscapeDataString(TextBoxisbn6.Text)
    ItemId(6) = System.Uri.EscapeDataString(TextBoxisbn7.Text)
    ItemId(7) = System.Uri.EscapeDataString(TextBoxisbn8.Text)
    ItemId(8) = System.Uri.EscapeDataString(TextBoxisbn9.Text)
    ItemId(9) = System.Uri.EscapeDataString(TextBoxisbn10.Text)

    Dim i As Integer = 0
    'For Each ItemId As String In ItemIds
    'Parallel.ForEach(ItemIds, Sub(ItemId)
    System.Threading.Tasks.Parallel.ForEach(ItemIds, Sub(ItemId)
                                                         'For Each ItemId As String In ItemIds()


                                                         'Next
                                                         ' Dim ItemId As String = System.IO.Path.GetFileName(currentFile)
                                                         My.Settings.ItemId = ItemId

                                                         Dim MyREST As New SprightlySoftAWS.REST

                                                         Dim RequestURL(i) As String
                                                         RequestURL(i) = "https://webservices.amazon.com/onca/xml?Service=AWSECommerceService&Operation=ItemLookup&Version=2011-08-01"
                                                         RequestURL(i) += "&SignatureVersion=2&SignatureMethod=HmacSHA256&Timestamp=" & Uri.EscapeDataString(DateTime.UtcNow.ToString("yyyy-MM-dd\THH:mm:ss.fff\Z"))
                                                         RequestURL(i) += "&AssociateTag="
                                                         RequestURL(i) += "&ResponseGroup=" & System.Uri.EscapeDataString("ItemAttributes,Large,OfferSummary,Offers,VariationSummary,Reviews")
                                                         RequestURL(i) += "&ItemId=" & System.Uri.EscapeDataString(ItemId)

                                                         'RequestURL(i) += "&ItemId=" & System.Uri.EscapeDataString(ItemId)

                                                         RequestURL(i) += "&IdType=ISBN"
                                                         RequestURL(i) += "&SearchIndex=Books"

                                                         Dim RequestMethod As String
                                                         RequestMethod = "GET"

                                                         Dim SignatureValue As String
                                                         SignatureValue = MyREST.GetSignatureVersion2Value(RequestURL(i), RequestMethod, "", "")

                                                         RequestURL(i) += "&Signature=" & System.Uri.EscapeDataString(SignatureValue)

                                                         Dim RetBool As Nullable(Of Boolean)
                                                         RetBool = MyREST.MakeRequest(RequestURL(i), RequestMethod, Nothing)

                                                         Debug.Print("")
                                                         Debug.Print(MyREST.LogData)
                                                         Debug.Print("")

                                                         Dim Y As Integer
                                                         Dim ResponseMessage As String = ""


                                                         If RetBool = True Then
                                                             Dim MyXmlDocument As System.Xml.XmlDocument
                                                             Dim MyXmlNamespaceManager As System.Xml.XmlNamespaceManager
                                                             Dim MyXmlNode As System.Xml.XmlNode
                                                             Dim MyXmlNodeList As System.Xml.XmlNodeList

                                                             MyXmlDocument = New System.Xml.XmlDocument
                                                             MyXmlDocument.LoadXml(MyREST.ResponseString)

                                                             MyXmlNamespaceManager = New System.Xml.XmlNamespaceManager(MyXmlDocument.NameTable)
                                                             MyXmlNamespaceManager.AddNamespace("amz", "http://webservices.amazon.com/AWSECommerceService/2011-08-01")

                                                             MyXmlNodeList = MyXmlDocument.SelectNodes("amz:ItemLookupResponse/amz:Items/amz:Item", MyXmlNamespaceManager)

                                                             If MyXmlNodeList.Count = 0 Then
                                                                 ResponseMessage = "Item not found."
                                                             Else

                                                                 For Each ItemXmlNode As System.Xml.XmlNode In MyXmlNodeList
                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:ASIN", MyXmlNamespaceManager)
                                                                     ResponseMessage += "Details of " & MyXmlNode.InnerText

                                                                     'Dim vbCrLf As New String(ValueType)

                                                                     ResponseMessage += vbCrLf
                                                                     ' ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:ItemAttributes/amz:Title", MyXmlNamespaceManager)
                                                                     ResponseMessage += "Title = " & MyXmlNode.InnerText

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:MediumImage/amz:URL", MyXmlNamespaceManager)
                                                                     ResponseMessage += "Image = " & MyXmlNode.InnerText

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNodeList = ItemXmlNode.SelectNodes("amz:ItemAttributes/amz:Author", MyXmlNamespaceManager)
                                                                     If IsNothing(MyXmlNodeList) = False Then
                                                                         ResponseMessage += "Author = "
                                                                         For Each MyXmlNode In MyXmlNodeList
                                                                             ResponseMessage += MyXmlNode.InnerText & ", "
                                                                         Next
                                                                     End If

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:ItemAttributes/amz:ListPrice/amz:FormattedPrice", MyXmlNamespaceManager)
                                                                     ResponseMessage += "ListPrice = "
                                                                     If IsNothing(MyXmlNode) = False Then
                                                                         ResponseMessage += MyXmlNode.InnerText
                                                                     End If

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:Offers/amz:Offer/amz:OfferAttributes/amz:Condition", MyXmlNamespaceManager)
                                                                     ResponseMessage += "Condition = " & MyXmlNode.InnerText

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:Offers/amz:TotalOffers", MyXmlNamespaceManager)
                                                                     ResponseMessage += "TotalOffers = " & MyXmlNode.InnerText

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:OfferSummary/amz:TotalNew", MyXmlNamespaceManager)
                                                                     ResponseMessage += "TotalNew = " & MyXmlNode.InnerText

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNodeList = ItemXmlNode.SelectNodes("amz:OfferSummary/amz:LowestNewPrice/amz:FormattedPrice", MyXmlNamespaceManager)
                                                                     ResponseMessage += "LowestNewPrice = "
                                                                     Y = 0
                                                                     For Each MyXmlNode In MyXmlNodeList
                                                                         If Y < 25 Then
                                                                             ResponseMessage += "" & MyXmlNode.InnerText & "  "
                                                                         End If
                                                                     Next

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:OfferSummary/amz:TotalUsed", MyXmlNamespaceManager)
                                                                     ResponseMessage += "TotalUsed = " & MyXmlNode.InnerText

                                                                     ResponseMessage += vbCrLf

                                                                     MyXmlNode = ItemXmlNode.SelectSingleNode("amz:OfferSummary/amz:LowestUsedPrice/amz:FormattedPrice", MyXmlNamespaceManager)
                                                                     ResponseMessage += "LowestUsedPrice = "
                                                                     If IsNothing(MyXmlNode) = False Then
                                                                         ResponseMessage += "" & MyXmlNode.InnerText
                                                                     Else
                                                                         ResponseMessage += "0"
                                                                     End If

                                                                     ResponseMessage += vbCrLf

                                                                     'MyXmlNode = ItemXmlNode.SelectSingleNode("amz:SalesRank", MyXmlNamespaceManager)
                                                                     'ResponseMessage += "SalesRank = " & MyXmlNode.InnerText

                                                                     'ResponseMessage += vbCrLf
                                                                 Next
                                                             End If

                                                             DialogOutput.Text = "Success"
                                                             DialogOutput.TextBoxOutput.Text += vbCrLf & ResponseMessage & vbCrLf


                                                         Else
                                                             ResponseMessage = FormatLogData(MyREST.RequestURL, MyREST.RequestMethod, MyREST.RequestHeaders, MyREST.ResponseStatusCode, MyREST.ResponseStatusDescription, MyREST.ResponseHeaders, MyREST.ResponseStringFormatted, MyREST.ErrorNumber, MyREST.ErrorDescription)

                                                             DialogOutput.Text = "Error"
                                                             DialogOutput.TextBoxOutput.Text = ResponseMessage
                                                             ' DialogOutput.ShowDialog(Me)
                                                             ' DialogOutput.Dispose()
                                                         End If
                                                         i = i + 1
                                                     End Sub)
    'Next
    DialogOutput.ShowDialog(Me)
    ClearTextBox(Me)
    sender.Enabled = True
End Sub

2 个答案:

答案 0 :(得分:0)

您可以使用nullables来捕获该错误。

Dim isbn As Integer?

答案 1 :(得分:0)

如果调试程序,黄色线路在哪里?