Get files one at a time from a folder in VB.NET - vb.net

Question

I am trying to read some text files path in a folder sequentially. However, I get only the first file.
I need to get the first file, execute a timer, get the next file path, execute a timer right up to the last file in the folder, and stop. How can I get around this?
Private zMailbox As String = "c:\Fold\"
Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) _
Handles Button1.Click
Timer1.Start()
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) _
Handles Timer1.Tick
Dim finfo As New IO.DirectoryInfo(zMailbox)
For Each fi In finfo.GetFiles("*.txt")
TextBox1.Text = fi.FullName
Next
End Sub
Thanks to the contributions below I got the code to work with the text box value. However, it gives the index count instead of the path which I want to retrieve.
Private zMailbox As String = "c:\Fold\"
Dim files As FileInfo()
Dim index As Integer = 0
Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) _
Handles Button1.Click
Dim finfo As New IO.DirectoryInfo(zMailbox)
files = finfo.GetFiles("*.txt")
Timer1.Start()
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) _
Handles Timer1.Tick
If index >= files.Length Then
index = 0
End If
TextBox1.Text = (ListBox1.Items.Add(files(index)))
index += 1
End Sub

Answer 1

Your code loads all the files in the Timer event and assign them to the TextBox1.Text property inside the loop. Every loop overwrites the data that has been written in the previous loop.
At the end of the loop you see only the last value.
To show sequentially the files inside the Timer Tick event, you need to read the directory content before starting the Timer in a global FileInfo array. Another global variable will be used as indexer to show a particular file from this FileInfo array in your Timer.Tick event.
The index will be incremented and, at the next Tick, you could show the next file
Dim files as FileInfo()
Dim index As Integer = 0
Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
Dim finfo As New IO.DirectoryInfo(zMailbox)
files = finfo.GetFiles("*.txt")
Timer1.Start()
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
if index >= files.Length Then
index = 0
End If
TextBox1.Text = files(index)
index += 1
End Sub
EDIT
According to your comment, you need to set the MultiLine property of the TextBox to true (using the form designer) and then, at every Tick, instead of replacing the Text property, append to it
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
if index >= files.Length Then
return ' Reached the end of the array. Stop the Timer???
End If
TextBox1.AppendText(files(index) & Environment.NewLine)
index += 1
End Sub
As a side note, if you want to show all file names together then it is not clear why you need a timer at all.
You could get the same result with code like this
Dim finfo As New IO.DirectoryInfo(zMailbox)
Dim files = finfo.EnumerateFiles("*.txt")
TextBox1.Text = string.Join(Environment.NewLine, files.Select(Function(x) x.FullName).ToArray())

Answer 2

On the original code you posted you where getting all files in the for loop each time the timer clicks.
After reading steve answer, and your comments, probably you always got all the files, but you override the textbox.text value.
TextBox1.Text += < String > & vbNewLine
Where < String >, of course, is the string returned by DirectoryInfo.GetFiles()
I think steve answer works just fine, but you are not implementing it well.

Answer 3

I would try and make this as easy as possible for you. You Microsoft's Reactive Framework for this. Just NuGet "Rx-Main".
Here's what you can then do:
finfo.GetFiles("*.txt").ToObservable() _
.Zip(Observable.Interval(TimeSpan.FromSeconds(1.0)), Function(f, _) f.Name) _
.ObserveOn(TextBox1) _
.Subscribe(Function(n) textbox_text += n + Environment.NewLine)
That's it. No timers. No separate methods. No need for module-level variables. Just one line of code and you're done.
It's processed on a background thread and then marshalled back to the UI via the .ObserveOn(TextBox1) call.
You can even keep a reference to the IDisposable returned by the .Subscribe(...) call to terminate the observable (timer) early.
Simple.

Answer 4

This seems a bit Rube Goldberg-ish. Just get all the files and loop through them in your Button_Click method:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim finfo As New IO.DirectoryInfo(zMailbox)
For Each fi In finfo.GetFiles("*.txt")
TextBox1.Text = fi.FullName
Next
End Sub