VB Migration Partner

KNOWLEDGE BASE - Forms and controls


Previous | Index | Next 

[HOWTO] Speed up For Each loops that iterate over the Controls collection

Iterating over all the controls on a form is a common operation in VB6 apps. For example, the following code clears the caption of all Label controls:

        Dim ctrl As Control
        For Each ctrl in Me.Controls
            If TypeOf ctrl Is Label Then ctrl.Caption = ""
        Next

VB Migration Partner converts the code as-is, replaces the Control variable with an Object variable:

        Dim ctrl As Object
        For Each ctrl in Me.Controls6
            If TypeOf ctrl Is VB6Label Then ctrl.Caption = ""
        Next

The replacement is necessary for two reasons. First, the Controls6 collection can include components (e.g. Timer and CommonDialog) which would cause a TypeMismatch exception if assigned to a System.Windows.Forms.Control variable. Second, using an Object variable avoids compilation errors when accessing the Caption property or another member that isn’t exposed by the .NET Control class.

Even if VB Migration Partner renders Control variables as Object variables by default, in some cases using the .NET Control class would work correctly and would deliver more efficient code because early binding would be used instead. More precisely, you should force VB Migration Partner to convert Control variables to System.Windows.Forms.Control variables if the following two conditions are both met:

  1. the form doesn’t contain nonvisible components such as Timer, Menu, or CommonDialog or you aren't interested in processing these components 
  2. the code inside the loop references members that are exposed by the .NET Control class.

You can force VB Migration Partner to convert a given Control variable to a System.Windows.Forms.Control variable by means of the SetType pragma, as in this code snippet:

        '## ctrl.SetType Control
        Dim ctrl As Control
        For Each ctrl in Me.Controls
            If TypeOf ctrl Is TextBox Then ctrl.Text = ""
        Next

Alternatively, you can convert all Control variables in the current file or project with the ChangeType pragma:

        '## project:ChangeType Control, Object
Previous | Index | Next 




Follow Francesco Balena on VB6 migration’s group on

LinkedIn





Read Microsoft Corp’s official case study of a VB6 conversion using VB Migration Partner.




Code Architects and its partners offers remote and onsite migration services.

More details




Subscribe to our free newsletter for useful VB6 migration tips and techniques.

newsletter



To learn more about your VB6 applications, run VB6 Analyzer on your source code and send us the generated text file. You will receive a detailed report about your VB6 applications and how VB Migration Partner can help you to quickly and effectively migrate it to .NET.

Get free advice



A fully-working, time-limited Trial Edition of VB Migration Partner allows you to test it against your actual code

Get the Trial




The price of VB Migration Partner depends on the size of the VB6 application, the type of license, and other factors

Request a quote




Migrating a VB6 application in 10 easy steps

Comparing VB Migration Partner with Upgrade Wizard

Migration tools: Feature Comparison Table

All whitepapers