Code to split a large text file into smaller chunks of file

This code is in VB.NET:

Private Sub btnBreak_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBreak.Click

        Dim tsInput As StreamReader

        Dim tsOp As StreamWriter

        Dim fi As FileInfo

        Dim iLineCtr, iCntPerFile, fileCnt As Integer

        Dim strLine, strFileNameGen As String

        Dim opFile As String

        Try

            tsInput = New StreamReader(txtFileName.Text)

            fi = New FileInfo(txtFileName.Text)

            iCntPerFile = Convert.ToInt32(txtlineCount.Text)

            fileCnt = 1

            strFileNameGen = txtOutput.Text + "\" + fi.Name.Remove(fi.Name.Length - 4)

            Do

                opFile = strFileNameGen + fileCnt.ToString("0000") + fi.Name.Substring(fi.Name.Length - 4)

                tsOp = New StreamWriter(opFile)

                For iLineCtr = 1 To iCntPerFile

                    If (Not tsInput.EndOfStream) Then

                        strLine = tsInput.ReadLine()

                        tsOp.WriteLine(strLine)

                    End If

                Next

                tsOp.Close()

                tsOp = Nothing

                fileCnt = fileCnt + 1

            Loop While (Not tsInput.EndOfStream)

        Catch ex As Exception

            MessageBox.Show(ex.Message.Trim())

        End Try

    End Sub