Question

What I want is for the app to read the first line from a text file and output it to the textReply textbox, then wait for X time before reading and outputting the next line.

Dim fileIn As New System.IO.StreamReader("C:\test.txt")
Dim strData As String = ""
While (Not (fileIn.EndOfStream))
    strData = fileIn.ReadLine()
    textReply.Text = textReply.Text & strData & vbCr
    System.Threading.Thread.Sleep(1000)
End While

As you can see I have tried sleeping the thread (not ideal as I want the app to stay responsive but thats another matter!) but every time it reads the whole file and dumps the lot into the textbox.

The reason is eventually it will be used for a serial connection to a device which needs time for the data transfer to the device and for the device to respond to each line sent.

Answer 1

You can create a Queue of string add each line to the list as you are reading the file, then you can poll it with a timer and add them to your textbox one at a time.

Public Class Form1
    Dim myQueue As Queue(Of String) = New Queue(Of String)

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Dim fileIn As New System.IO.StreamReader("C:\test.txt")
        Timer1.Start()
        Dim strData As String = ""
        While (Not (fileIn.EndOfStream))
            strData = fileIn.ReadLine()
            myQueue.Enqueue(strData)
        End While
    End Sub

    Private Sub Timer1_Tick(sender As System.Object, e As System.EventArgs) Handles Timer1.Tick
        If myQueue.Count > 0 Then
            textReply.Text += myQueue.Dequeue & vbCrLf
        End If
    End Sub
End Class