Object reference not set to an instance of an object.

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i am using below code for searching but its properly work on only title criteria and when i select the another criteria like author, publisher etc its give an error "Object reference not set to an instance of an object."

code:

VB

Private Sub Btn_Show_Click(sender As Object, e As RoutedEventArgs)
       Dim dt As New DataTable()
       Dim SearchCriteria = cmbSearch.Text
       dt.Columns.Add("Title", GetType(String))
       dt.Columns.Add("Author", GetType(String))
       dt.Columns.Add("AccessionNo", GetType(String))
       dt.Columns.Add("Location", GetType(String))
       dt.Columns.Add("Status", GetType(String))
       Dim xmldoc As New XmlDocument()
       xmldoc.Load("C:\Users\Shahrukh\Documents\Visual Studio 2012\Projects\Simple search1\Simple search1\New folder\Data.xml")
       Dim nodeList As XmlNodeList = xmldoc.SelectNodes("/NewDataSet/Table")


       If SearchCriteria = "Title" Then
           For Each node As XmlNode In nodeList
               Dim dtrow As DataRow = dt.NewRow()
               If (LCase(node("title").InnerText).Contains(LCase(txtSearch.Text()))) Then
                   dtrow("Title") = node("title").InnerText
                   dtrow("Author") = node("Author").InnerText
                   dtrow("AccessionNo") = node("AccessionNo").InnerText
                   dtrow("Location") = node("location").InnerText
                   dtrow("Status") = node("status").InnerText
                   dt.Rows.Add(dtrow)
               End If
           Next
       End If

       If SearchCriteria = "Author" Then
           For Each nodeAuthor As XmlNode In nodeList
               Dim dtrow As DataRow = dt.NewRow()
               If (LCase(nodeAuthor("Author").InnerText).Contains(LCase(txtSearch.Text()))) Then
                   dtrow("title") = nodeAuthor("title").InnerText
                   dtrow("Author") = nodeAuthor("Author").InnerText
                   dtrow("AccessionNo") = nodeAuthor("AccessionNo").InnerText
                   dtrow("location") = nodeAuthor("location").InnerText
                   dtrow("status") = nodeAuthor("status").InnerText
                   dt.Rows.Add(dtrow)
               End If
           Next
       End If
       dGridResults.ItemsSource = dt.DefaultView
   End Sub

Posted 4-Nov-15 8:50am

Member 12112060

Updated 4-Nov-15 9:24am

Suvendu Shekhar Giri

v2

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Richard Deeming 6-Nov-15 13:51pm

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Matt T Heffron · Answer 1 · 2015-11-04T09:34:00

You aren't consistent in the UPPER/lower case of the strings you use to index into dtrow and they don't always match the column names you specified above.

VB

Private Sub Btn_Show_Click(sender As Object, e As RoutedEventArgs)
       Dim dt As New DataTable()
       Dim SearchCriteria = cmbSearch.Text
       dt.Columns.Add("Title", GetType(String))
       dt.Columns.Add("Author", GetType(String))
       dt.Columns.Add("AccessionNo", GetType(String))
       dt.Columns.Add("Location", GetType(String))
       dt.Columns.Add("Status", GetType(String))
       Dim xmldoc As New XmlDocument()
       xmldoc.Load("C:\Users\Shahrukh\Documents\Visual Studio 2012\Projects\Simple search1\Simple search1\New folder\Data.xml")
       Dim nodeList As XmlNodeList = xmldoc.SelectNodes("/NewDataSet/Table")
 

       If SearchCriteria = "Title" Then
           For Each node As XmlNode In nodeList
               Dim dtrow As DataRow = dt.NewRow()
               If (LCase(node("title").InnerText).Contains(LCase(txtSearch.Text()))) Then
                   dtrow("Title") = node("title").InnerText
                   dtrow("Author") = node("Author").InnerText
                   dtrow("AccessionNo") = node("AccessionNo").InnerText
                   dtrow("Location") = node("location").InnerText
                   dtrow("Status") = node("status").InnerText
                   dt.Rows.Add(dtrow)
               End If
           Next
       End If
 
       If SearchCriteria = "Author" Then
           For Each nodeAuthor As XmlNode In nodeList
               Dim dtrow As DataRow = dt.NewRow()
               If (LCase(nodeAuthor("Author").InnerText).Contains(LCase(txtSearch.Text()))) Then
                   dtrow("Title") = nodeAuthor("title").InnerText  ' fixed
                   dtrow("Author") = nodeAuthor("Author").InnerText
                   dtrow("AccessionNo") = nodeAuthor("AccessionNo").InnerText
                   dtrow("Location") = nodeAuthor("location").InnerText  ' fixed
                   dtrow("Status") = nodeAuthor("status").InnerText  ' fixed
                   dt.Rows.Add(dtrow)
               End If
           Next
       End If
       dGridResults.ItemsSource = dt.DefaultView
   End Sub

You should use named constants instead of in-line strings to avoid this. The constants define the string value and the compiler will enforce your using the correct casing/spelling of the names.