Option Compare Text ' Case insensitive search.
' Use Option Compare Binary for case sensitive search.

Public Class Words
    ' Object to store the current state, for passing to the caller.
    Public Class CurrentState
        Public LinesCounted As Integer
        Public WordsMatched As Integer
    End Class

    Public SourceFile As String
    Public CompareString As String
    Private WordCount As Integer = 0
    Private LinesCounted As Integer = 0

    Public Sub CountWords( _
        ByVal worker As System.ComponentModel.BackgroundWorker, _
        ByVal e As System.ComponentModel.DoWorkEventArgs _
    )
        ' Initialize the variables.
        Dim state As New CurrentState
        Dim myStream As System.IO.StreamReader = Nothing
        Dim line = ""
        Dim elapsedTime = 20
        Dim lastReportDateTime = Now

        If CompareString Is Nothing Or _
                CompareString = System.String.Empty Then
            Throw New Exception("CompareString not specified.")
        End If

        Try
            ' Open a new stream.
            myStream = My.Computer.FileSystem.OpenTextFileReader(SourceFile)
            ' Do while there are lines remaining in the file to be read.
            Do While Not myStream.EndOfStream
                If worker.CancellationPending Then
                    e.Cancel = True
                    Exit Do
                Else
                    line = myStream.ReadLine
                    WordCount += CountInString(line, CompareString)
                    LinesCounted += 1

                    ' Raise an event so the form can monitor progress.
                    If Now > lastReportDateTime.AddMilliseconds(elapsedTime) Then
                        state.LinesCounted = LinesCounted
                        state.WordsMatched = WordCount
                        worker.ReportProgress(0, state)
                        lastReportDateTime = Now.AddMilliseconds(elapsedTime)
                    End If
                End If
            Loop

            ' Report the final count values.
            state.LinesCounted = LinesCounted
            state.WordsMatched = WordCount
            worker.ReportProgress(0, state)
        Finally
            If myStream IsNot Nothing Then
                ' Close the file.
                myStream.Close()
            End If
        End Try
    End Sub

    Private Function CountInString( _
        ByVal SourceString As String, _
        ByVal CompareString As String _
    ) As Integer
        ' This function counts the number of times
        ' a word is found in a line.
        If SourceString Is Nothing Then
            Return 0
        End If

        Dim regex As New System.Text.RegularExpressions.Regex( _
            System.Text.RegularExpressions.Regex.Escape(CompareString))
        Dim matches As System.Text.RegularExpressions.MatchCollection
        matches = regex.Matches(SourceString)
        Return matches.Count
    End Function
End Class

Private Sub BackgroundWorker1_DoWork( _
    ByVal sender As Object, _
    ByVal e As System.ComponentModel.DoWorkEventArgs) _
    Handles BackgroundWorker1.DoWork

    ' This event handler is where the actual work is done.
    ' This method runs on the background thread.

    ' Get the BackgroundWorker object that raised this event.
    Dim worker As System.ComponentModel.BackgroundWorker
    worker = CType(sender, System.ComponentModel.BackgroundWorker)

    ' Get the Works object and call the main method.
    Dim WC As Words = CType(e.Argument, Words)
    WC.CountWords(worker, e)
End Sub

Sub StartThread()
    ' This method runs on the main thread.

    Me.WordsCounted.Text = "0"

    ' Initialize the object that the background worker calls.
    Dim WC As New Words
    WC.CompareString = Me.CompareString.Text
    WC.SourceFile = Me.SourceFile.Text

    ' Start the asynchronous operation.
    BackgroundWorker1.RunWorkerAsync(WC)
End Sub

Private Sub Start_Click( _
    ByVal sender As System.Object, _
    ByVal e As System.EventArgs) _
    Handles Start.Click

    StartThread()
End Sub