How to prevent UI from freezing during lengthy process?

Question

I need to write a VB.Net 2008 applet to go through all the fixed-drives looking for some files. If I put the code in ButtonClick(), the UI freezes until the code is done:

Answer 1

The key is to seperate the UI code from the actual functionality code. The time-consuming functionality should run on a seperate thread. To achieve this, you can either:

1. Create and start a Thread object by yourself
2. Create a Delegate and use asynchronous invokation (using BeginInvoke).
3. Create and start a BackgroundWorker.

As you mentioned, you should avoid Application.DoEvents(). A proper breakdown of the application's functionality will allow you to create an application which is designed to be responsive, rather than creating a non-responsive application with DoEvents "fixes" (which is costly, considered bad practice, and implies a bad design).

Since your method doesn't return a value and doesn't update the UI, the fastest solution might be creating a Delegate and using "fire and forget" asynchronous invokation:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Call New Action(AddressOf DrivesIteration).BeginInvoke(Nothing, Nothing)
End Sub

Private Sub DrivesIteration()
    Dim drive As DriveInfo
    Dim filelist As Collections.ObjectModel.ReadOnlyCollection(Of String)
    Dim filepath As String

    For Each drive In DriveInfo.GetDrives()
        If drive.DriveType = DriveType.Fixed Then
            filelist = My.Computer.FileSystem.GetFiles(drive.ToString, FileIO.SearchOption.SearchAllSubDirectories, "MyFiles.*")
            For Each filepath In filelist
                DoStuff(...)
            Next
        End If
    Next 
End Sub

BTW, For..Next blocks no longer have to end with "Next (something)", it is obsolete - VB now infers the (something) by itself, so there is no need to state it explicitly.