Problems persisting a datatable between forms in an interop dll

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  12 years ago

  by sammyonline

  Sammy

  , United States

  Joined 13 years ago

   For test purposes, i have first created my program as a standalone exe project and everything works fine.  When i re-create the project as an interop dll, i get an error.

  In both projects, i create a datatable in a module file with the following code
   

  Friend SelectedHistoryTable As DataTable

  Form1 is called from FoxPro via interop.

  Form1 then calls Form2 which adds the column names to the table

  SelectedHistoryTable = New DataTable("SelectedHistory")
  
          Dim DateTimeCol As New DataColumn("DateTime")
          SelectedHistoryTable.Columns.Add(DateTimeCol)
  
          For j As Integer = 0 To lstTags.Items.Count - 1
              Dim NewTagCol As New DataColumn(lstTags.Items.Item(j).ToString())
              SelectedHistoryTable.Columns.Add(NewTagCol)
          Next j

  Form1 then calls Form3 which adds data to the table

   Dim NewRow As DataRow
              NewRow = SelectedHistoryTable.NewRow()

   
  This works fine as a standalone app, but i cant get this section of code working when i am compiling it as a dll.

   The last line (that creates the newrow) causes a NullReferenceException

  Object reference not set to an instance of an object.

  I can't see why this table does not have scope on this form in the dll project but it does in the standalone project.

   

  Can anyone help?

   

   

   

   

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