Referencing an running instance of a form(VB6 equiv: loop through the Forms collec.)

[Guest Andrejko]

Since the Forms collection no longer exists in VB.NET, how do you determine whether a form is already running?

In other words, what is the .NET equivalent of the following VB6 code:

 

Sub CheckFormStatus(ByRef f As System.Windows.Forms.Form)

Dim I As Short

For I = 0 To Forms.Count - 1

If Forms(I).Tag = f.Tag Then

'this window is already loaded - check if minimized

If Forms(I).WindowState = 1 Then

f.WindowState = System.Windows.Forms.FormWindowState.Normal

End If

Exit For

End If

Next I

f.BringToFront()

End Sub

[divil]

a) That's not VB6 code.

b) You don't.

 

You write code to keep track of what forms are loaded yourself. VB6 implicitly created an instance of a form with the same name as the form class itself, which led to laziness with some programmers. You should keep track yourself of the instances of forms loaded.

[Guest Andrejko]

You are right

 

Actualy, you are right. That is a funky mix of VB6 and VB.NET that was generated when I ran the Upgrade Wizard.

 

Your suggested solution makes perfect sense (to a Java programmer like me, at least ;), and I would gladly go down that route if I were developing a project from scratch. Unfortunately, I am dealing with a rather large VB6 app that needs to become a rather large VB.NET app in less than a month :)

 

I was just wondering whether there was an easy way of simulating the aforementioned functionality in .NET (without implementing my own Forms collection)

 

I did come up with a potential solution of my own:

Create a Shared (static in C#) member, similar to DefInstance, called isRunning (or something to that effect) which would be inside each form in the application. Any thoughts?

[Guest TheIrishCoder]

There is no forms collection in .net. Microsoft suggest you subclass the collection class and create your own custom forms collection. Every time you create a reference to a form you would add it to your collection which at any time would ideally return a reference to that form object.

[divil]

You could have a global collection in your project, and inside the constructor of each form you could add the instance to it.

[Guest Andrejko]

You could have a global collection in your project, and inside the constructor of each form you could add the instance to it.

 

You mean a reference, i take it?

In .NET, there is no such thing as global variables. And if it was global, individual forms would not need a reference. But I understand what you mean. Going back to my original post:

 

Originally posted by Andrejko

I was just wondering whether there was an easy way of simulating the aforementioned functionality in .NET (without implementing my own Forms collection)

 

And:

 

Originally posted by Andrejko

I did come up with a potential solution of my own:

Create a Shared (static in C#) member, similar to DefInstance, called isRunning (or something to that effect) which would be inside each form in the application. Any thoughts?

[divil]

Create a module, and make a public collection variable in there to hold all form instances. That is, to all intents and purposes, a global variable. This is a working solution, I've tried it.

[Guest Andrejko]

[PLAIN]easy, elegant solution [attempt][/PLAIN]

 

Here is an implementation of the solution I mentioned before:

 

 
#Region "AK: Forms Collection workaround (detecting whether a form is instantiated - 'running')"
   Private Shared m_akIsInstantiated As Boolean = False
   Public Shared Property isInstantiated() As Boolean
       Get
           If m_vb6FormDefInstance Is Nothing OrElse m_vb6FormDefInstance.IsDisposed Then
               m_akIsInstantiated = False
           Else
               m_akIsInstantiated = True
           End If
           isInstantiated = m_akIsInstantiated
       End Get
       Set(ByVal Value As Boolean)
           m_akIsInstantiated = Value
       End Set
   End Property
#End Region
#Region "AK: Modified Upgrade Support "
   Private Shared m_vb6FormDefInstance As Form2
   Private Shared m_InitializingDefInstance As Boolean
   Public Shared Property DefInstance() As Form2
       Get
           If m_vb6FormDefInstance Is Nothing OrElse m_vb6FormDefInstance.IsDisposed Then
               m_InitializingDefInstance = True
               m_vb6FormDefInstance = New Form2()
               m_InitializingDefInstance = False
           End If
           DefInstance = m_vb6FormDefInstance
       End Get
       Set(ByVal Value As Form2)
           m_vb6FormDefInstance = Value
       End Set
   End Property
#End Region  

 

This code goes inside the Public Sub New()

 
'### AK: code for IsInstantiated member - see AK: Forms Collection workaround Region 
       m_akIsInstantiated = True

       If m_vb6FormDefInstance Is Nothing Then
           If m_InitializingDefInstance Then
               m_vb6FormDefInstance = Me
           Else
               Try
                   'For the start-up form, the first instance created is the default instance.
                   If System.Reflection.Assembly.GetExecutingAssembly.EntryPoint.DeclaringType Is Me.GetType Then
                       m_vb6FormDefInstance = Me
                   End If
               Catch
               End Try
           End If
       End If   

 

Now, to check whether a form is already instantiated, just do

MyForm.IsInstantiated()

.

Caveat:

This code works in debug mode, but fails whan actually running it. I am currently debugging it, and will post a working solution as soon as I have one.

Does anyone see why this would be failing outside of debug mode?

[Guest Andrejko]

Create a module, and make a public collection variable in there to hold all form instances. That is, to all intents and purposes, a global variable. This is a working solution, I've tried it.

 

I know that the solution you are proposing is a working one. I am not disputing that, as I have said in my previous posts. I am asking for a simpler, quicker solution (like the one I posted above).