[2008] UserControl Item Collection

[NickThissen]

Hi,

I am trying to create a UserControl that mimics the Options screen from the Visual Studio (2008) IDE and many other programs: a list of all the 'sub-options' which give you the corresponding options when selected.
My idea was that it worked pretty much the same as a TabControl except that the 'tab headers' are now the list entries and the tabpages are simple Panels that get hidden/unhidden when they are needed.

Now, I want the user to be able to add options panels (or "Pages") from the designer so he doesn't have to do it via code obviously.

I created a Public Property called Pages() of type "Collection" that will hold the Pages (which are of another UserControl control type called "ctrlPage", inherited from the Panel control).

I can access this property from the designer, but I can only add 'Objects'. How can I specify that these Pages are actually of the type "ctrlPage" instead of just Object?

I have tried replacing the Collection with a "List(Of ctrlPage)" but that keeps giving me an error about Panels and ctrlPage not being serializable or something...


The pages property is just this:
Private _Pages As Collection

Public Property Pages() As Collection
        Get
            If _Pages Is Nothing Then _Pages = New Collection()
            Return _Pages
        End Get
        Set(ByVal value As Collection)
            _Pages = value
        End Set
    End Property

[NickThissen]

EDIT
Nevermind that, I found something else.

EDIT2 (See bold notes)


Instead of creating the Pages of type Collection, I created a new class (called clsPageCollection) inheriting from 'CollectionBase':

Public Class clsPageCollection
    Inherits CollectionBase
 
    Default Public Property Item(ByVal index As Integer) As ctrlPage
        Get
            Return CType(List(index), ctrlPage)
        End Get
        Set(ByVal value As ctrlPage)
            List(index) = value
        End Set
    End Property
 
    Public Function Add(ByVal value As ctrlPage) As Integer
        Return List.Add(value)
    End Function
 
End Class

I am getting closer now: in the Pages collection of my UserControl in the designer, I can now see the properties of the default Page (which I add by code).

However, when I click the 'Add' button to add a new page it says:
Constructor on type 'Options.ctrlPage' not found.
(It does not say this anymore)

Now, if I can remember correctly, the Constructor is the "Public Sub New()" sub that calls the InitializeComponent method, right?
If so, it is definitely there...?:

Public Class ctrlPage
 
    Public Sub New()
 
        ' This call is required by the Windows Form Designer.
        InitializeComponent()
 
        ' Add any initialization after the InitializeComponent() call.
        Me.Dock = DockStyle.Fill
        Me.Name = "Default"
 
        Me.Controls.Add(Label1)
        Label1.Top = 0
        Label1.Left = 0
        Label1.Text = "Default"
    End Sub
 
End Class

What is going on?


I don't know why but it is working now!

However, when I use the designer to add a few pages, the 'Form1.Designer.vb' code comes out wrong... I have no control over this code creating, have I? so what can I do about this?

It looks like this (the error is simply "Syntax error")

'
        'CtrlOptions1
        '
        Me.CtrlOptions1.Location = New System.Drawing.Point(12, 12)
        Me.CtrlOptions1.Name = "CtrlOptions1"
New Options.clsPageCollection.Add(Me.CtrlPage1)    'error here
New Options.clsPageCollection.Add(Me.CtrlPage2)    'error here
        Me.CtrlOptions1.Size = New System.Drawing.Size(407, 405)
        Me.CtrlOptions1.TabIndex = 0

It seems to be exactly what is described here:
http://www.experts-exchange.com/Prog..._23214852.html
But since I have no subscription to this site I cannot see the solutions...

[jmcilhinney]

The Collection class is a holdover from VB6 that should not be used at all in new VB.NET code.

The CollectionBase class was introduced in .NET 1.0 but became redundant in .NET 2.0 with the introduction of generics and the System.Collections.ObjectModel.Collection(Of T) class. In your case the code should be:

Public Class PageCollection
    Inherits System.Collections.ObjectModel.Collection(Of Page)
End Class

That's it. All the standard collection functionality is inherited so there's no need to declare your own Item property or Add method. If you do want to add custom functionality, like validation on addition, then the Collection(Of T) class provides protected members you can override for that.

[NickThissen]

Thanks for clarifying that. I thought the Collection was new in VB.NET lol, never seen it in VB6!

Anyway, when I do that, the objects in my Pages collection (in the designer) are simply "Objects" once again, and there are no properties I can set.

When I add the Item() and Add() methods like this, it does have properties again like usual, BUT the Syntax Error I described above appears again...

Public Class clsPageCollection
    Inherits System.Collections.ObjectModel.Collection(Of ctrlPage)
 
    Default Public Overloads Property Item(ByVal index As Integer) As ctrlPage
        Get
            Return MyBase.Item(index)
        End Get
        Set(ByVal value As ctrlPage)
            MyBase.Item(index) = value
        End Set
    End Property
 
    Public Overloads Sub Add(ByVal value As ctrlPage)
        MyBase.Add(value)
    End Sub
 
End Class

[jmcilhinney]

There's no need or reason for you to be defining those members. I specifically said in my last post:

That's it. All the standard collection functionality is inherited so there's no need to declare your own Item property or Add method.

Your class already has an Item property and an Add method simply by inheriting the Collection(Of T) class. I suggest that you read the documentation for the class, which you really should be doing when using new classes anyway.

As for design-time support, it's up to you to add that yourself. Your property is a custom type and its items are a custom type, so the designer isn't going to just whip up an editor for you. You have to design your own editor and then tell the designer to use it for your property by applying the appropriate attribute(s).

[NickThissen]

Yes, and I tried that, I just had a 'blank' class that only inherited the Collection(Of T) class.
When I used that, I was back to my first problem: the objects in the 'collection designer' (I don't know what it's called, but it's the same thing you can use to add TabPages, or ListboxItems etc) were simply "Objects" and not "ctrlPages".

When I re-added those members they changed back to 'ctrlPages' and I could set any of the properties I have in the ctrlPage class.
(But then, the Syntax error comes up again).

I didn't have time yet to read the full documentation yet but I skimmed through it but didn't see anything related to my problem so quickly.