vb.net arcmap add-in loop through a dbf file get 'System.NullReferenceException' error

Question

I am using vb.net arcmap add-in.

I encounter a System.NullReferenceException error and cause arcmap crash. The workflow in my vb.net code is:

(1) create a ShapefileWorkspaceFactory

(2) use the workspace to open a DBF file as ITable

(3) loop through each record and get related value

The code I am using:

    Dim pWSF As ShapefileWorkspaceFactory = New ESRI.ArcGIS.DataSourcesFile.ShapefileWorkspaceFactory()
    Dim pWS As ESRI.ArcGIS.Geodatabase.IWorkspace = pWSF.OpenFromFile("D:/dev/local", 0)
    Dim pFws As ESRI.ArcGIS.Geodatabase.IFeatureWorkspace = CType(pWS, ESRI.ArcGIS.Geodatabase.IFeatureWorkspace)
    Dim pTable As ESRI.ArcGIS.Geodatabase.ITable = pFws.OpenTable("Segment_line_intersect")
    Dim pCur As ESRI.ArcGIS.Geodatabase.ICursor = pTable.Search(Nothing, False)
    Dim queryFilter As IQueryFilter = New QueryFilterClass()
    Dim pFieldIndex1 As Integer = pTable.Fields.FindField("Segment_ID")
    Dim pFieldIndex2 As Integer = pTable.Fields.FindField("DrainName")

    Dim pRow As ESRI.ArcGIS.Geodatabase.IRow = pCur.NextRow
    Dim SegmentID As String
    Dim DrainName As String

    Do Until pRow Is Nothing
        pRow = pCur.NextRow

        SegmentID = pRow.Value(pFieldIndex1)
        DrainName = pRow.Value(pFieldIndex2)

        MsgBox("SegmentID = " + SegmentID)
        MsgBox("DrainName = " + DrainName)

    Loop

All the values of SegmentID and DrainName can be retrieved correctly, but once all the values retrieved, the map crash. I use debug mode to track the error and get 'System.NullReferenceException' error.

I believe there is something wrong with my code, but I cannot tell what cause the issue.

I am using arcmap 10.2.2.

Answer 1

This line:

pRow = pCur.NextRow

should be at the end of your loop

Do Until pRow Is Nothing

    SegmentID = pRow.Value(pFieldIndex1)
    DrainName = pRow.Value(pFieldIndex2)

    MsgBox("SegmentID = " + SegmentID)
    MsgBox("DrainName = " + DrainName)

    pRow = pCur.NextRow

Loop

I think it's failing because you're trying to retrieve a value when pRow is null. Plus you were skipping the first record of your table because you called NextRow twice before starting your logic.