How to most efficiently replace this code to vb.net version? - vb.net

Question

Public Function fileToColHarvest(ByRef stream As Scripting.TextStream, Optional ByRef limit As Integer = 2000000, Optional ByRef unique As Boolean = False, Optional ByRef FirstSectionAsKey As Boolean = False, Optional ByRef prob As Double = 1) As Generic.List(Of String)
Dim buffer As String
Dim i As Integer
If prob < 1 Then
End If
fileToColHarvest = New Generic.List(Of String)
Do While (Not (stream.AtEndOfStream))
i = i + 1
System.Windows.Forms.Application.DoEvents()
'If Microsoft.VisualBasic.Rnd < 0.01 Then
' appendToTextFile CStr(fileToColHarvest.Count) + "|" + microsoft.visualbasic.str(i) + "|" + buffer, RESULT, ForWriting
'End If
buffer = stream.ReadLine
'buffer = Microsoft.VisualBasic.Replace(buffer, " ", "+")
If Microsoft.VisualBasic.Rnd() < prob Then
If unique Then
If Not FirstSectionAsKey Then
fileToColHarvest.AddIfNotExist(buffer)
Else
fileToColHarvest.AddIfNotExist(buffer)
End If
Else
fileToColHarvest.Add(buffer)
End If
End If
If fileToColHarvest.Count() >= limit Then
Exit Do
End If
Loop
End Function
Basically I want to get rid Scripting.TextStream.
Also I want to read the text line by line

Answer 1

You can use StreamReader and asynchronous ReadLineAsync method.
Asynchronous approach will replace "ugly" Application.DoEvents()
Public Async Function FileToColHarvest(
pathToFile As String,
limit As Integer,
isUnique As Boolean,
isFirstSectionAsKey As Boolean,
prob As Single) As Task(Of List(Of String))
Dim lines = New List(Of String)()
Dim uniqueLines = New HashSet(Of String)()
Using stream As New FileStream(pathToFile, FileMode.Open)
Using reader As New StreamReader(stream)
While reader.EndOfStream = False
'Await will prevent blocking UI thread
var line = Await reader.ReadLineAsync()
If prob < VBMath.Rnd() Then Continue While
' I have removed check of isFirstSectionAsKey
' because based on your code it does same thing
If isUnique Then
uniqueLines.Add(line)
If uniqueLines.Count >= limit Then Return uniqueLines.ToList()
Else
lines.Add(line)
If lines.Count >= limit Then Return lines
End If
End While
End Using
End Using
Return If(isUnique, uniqueLines.ToList(), lines)
End Function
Not related but isUnique argument divide this method in two different logic - so I suggest instead of parameter introduce two different methods
FileToColHarvest(...)
FileToColHarvestWithUniqueOnly(...)