Dynamically edit Contents of a CSV file using VB.net

Question

I have this code

  Dim fileReader As System.IO.StreamReader
        fileReader =
        My.Computer.FileSystem.OpenTextFileReader("Filepath")

        Dim stringReader As String
        'read csv file from first to last line
        While fileReader.ReadLine <> ""
            'get data of line
            stringReader = fileReader.ReadLine()
            'check the number of commas in the line
            Dim meh As String() = stringReader.Split(",")
            If meh.Length > 14 Then

                My.Computer.FileSystem.WriteAllText("Filepath", "asd", True)

            ElseIf meh.Length < 14 Then

                My.Computer.FileSystem.WriteAllText("Filepath", "asd", True)

            ElseIf meh.Length = 14 Then

                MsgBox("This line of the file has " & stringReader & meh.Length & "commas")

            End If

        End While
        End
    End Sub

To explain, the above code would check EACH line of a CSV file to check weather the contents has 14 commas('). Then if that line has more commas, the code will reduce it to 14, and if not, it would write commas so that it would be equal to 14. The above conditions are not created yet, so the code is just for testing. I read something about WriteAllText and this code gives me the error :

The process cannot access the file 'filepath' because it is being used by another process.

Which, I think, means that I cant edit the CSV file because I'm currently using its data.

My question is, how could I edit the contents of the CSV file even when I am checking its contents?

Please do disregard this code

My.Computer.FileSystem.WriteAllText("Filepath", "asd", True)

as I use this code just for testing, if ever I could manage to write it to the CSV file.

I Thank you for all your help.

You cannot write to a file already open for reading. Unless the file is very large you could use File.ReadAllLines() to load all the data so you can close the file and write to it. It looks like that is all that applet does, but usually you would want to be sure to close and dispose of streams - not doing so can result in the same error; and End is not a good way to exit a NET app. — Ňɏssa Pøngjǣrdenlarp
– Ňɏssa Pøngjǣrdenlarp, Commented Nov 26, 2016 at 13:58
Sorry for the 'End' @Plutonix I should've disposed it. What might you suggest? — Mr.J
– Mr.J, Commented Nov 28, 2016 at 0:10
If it is a Winforms app, Me.Close on the main form will end it — Ňɏssa Pøngjǣrdenlarp
– Ňɏssa Pøngjǣrdenlarp, Commented Nov 28, 2016 at 0:21

Tyler · Accepted Answer · 2016-11-28 10:18:56Z

If your CSV is not too big, you can read it in memory and work with it. When you have finish you can write it again on disk.

    'Declare 2 List (or you can work directly with one)
    Dim ListLines As New List(Of String)
    Dim ListLinesNEW As New List(Of String)

    'Read the file
    Using MyCSVread As New IO.FileStream("C:\MyCSV.csv", IO.FileMode.Open, IO.FileAccess.ReadWrite)

      'Read all the lines and put it in a list of T (string)  
      Using sReader As IO.StreamReader = New IO.StreamReader(MyCSVread)
            Do While sReader.Peek >= 0
                ListLines.Add(sReader.ReadLine)
            Loop
        End Using
    End Using

    'Your code for work with the line. Here you can write the new lines in the NEW list of string or work directly in the first
    For L As Integer = 0 To ListLines.Count - 1
        Dim meh As String() = ListLines(L).Split(",")
        If meh.Length > 14 Then
            'your code ...
        ElseIf meh.Length < 14 Then
            'your code ...
        ElseIf meh.Length = 14 Then
            MessageBox.Show("The line " & (ListLines(L) + 1) & " of the file has " & meh.Length & "commas", "MyApp", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
        End If
    Next

    'Open again the file for write
    Using MyCSVwrite As New IO.FileStream("C:\MyCSV.csv", IO.FileMode.Open, IO.FileAccess.ReadWrite)

        'Write back the file with the new lines
        Using sWriter As IO.StreamWriter = New IO.StreamWriter(MyCSVwrite)
            For Each sLine In ListLinesNEW.ToArray
                sWriter.WriteLine(sLine)
            Next
        End Using
    End Using

The "Using" auto close the filestream or a streamreader/write or what you use. Then you will not have problem like "file already in use".

Hope this help.

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