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creating a new control

Posted on 2007-11-29
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Last Modified: 2013-11-26
I've created my first custom control - a combobox.
Took a bit of digging to get it laid down right, but I think I have it now.
However, on my main form, I have a sub that is called by the containing comboboxes there.
I'd like to be able to call the same sub from my custom class.  I imagine I could just copy/paste it to the new class, but I'm curious if there's a more efficient way?

Also - my selectionchange event isn't firing...I must have missed something...  :(

Public Class CustomCombo

    Inherits ComboBox

    Public WithEvents CustomCombo As ComboBox

  

    Public Sub New()

        MyBase.Width = 145

    End Sub

 

  Private Sub CustomCombo_SelectionChangeCommitted(ByVal sender As Object, ByVal e As System.EventArgs) Handles CustomCombo.SelectionChangeCommitted

        CustomCombo.Items.Clear()

        CustomCombo.Visible = True

  End Sub

End Class

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Question by:sirbounty
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Assisted Solution

by:Bob Learned
Bob Learned earned 100 total points
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The interesting thing is that you have an instance of another control within your custom control.  

You only need this:
Public Class CustomCombo

    Inherits ComboBox

  

    Public Sub New()

        MyBase.Width = 145

    End Sub

 

End Class

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Author Comment

by:sirbounty
Comment Utility
When I remove the WithEvents though, I get errors on this sub (the CustomCombo is underlined)


Private Sub CustomCombo_SelectionChangeCommitted(ByVal sender As Object, ByVal e As System.EventArgs) Handles CustomCombo.SelectionChangeCommitted

   CustomCombo.Items.Clear()

   CustomCombo.Visible = True

End Sub

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Expert Comment

by:Bob Learned
Comment Utility
I think that you misunderstood what I meant.  When you are creating a custom control, then you don't really need an internal control instance.  The class that you create is the control, and you should have that event handler outside of the class, on the form where you created the instance of the control.

Bob
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Author Comment

by:sirbounty
Comment Utility
Hmm - I suppose I still don't understand.  This is my first attempt at creating a custom class/control, so maybe that's why this is so difficult for me...I found the 'withevents' item on another site, and it worked, tho apparently it's not the right route to take.

I was actually taking advice on how to solve a dilema from a comment made at http:/Q_22987698.html#20366705

Basically my situation calls for a dynamically created 'main' combo to reference a partner combo.  As the main combo is selected, the secondary gets populated with items that reference what was chosen in the main combo.
My thoughts were to use the tag property, but from that thread, it seemed like the better route was to create a subclass and add additional properties.

If I'm going to create this subclass, I need someway of identifying that a selection was made...and then some way to point it to it's corresponding partner combo (though I'm still not convinced that this is even the right way to go...)
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Expert Comment

by:jcoehoorn
Comment Utility
Just add a plain vanilla class to your project called CustomCombo and make it look like this:

    Public Class CustomCombo
        Inherits ComboBox

        Private Sub CustomCombo_SelectionChangeCommitted(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.SelectionChangeCommitted

        End Sub
    End Class

See how it uses "Me" instead of CustomCombo?  Remember, you'll also need to add a property that will be used so this new control knows about it's partner, and knows whether it's the parent or the child.
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Author Comment

by:sirbounty
Comment Utility
Great - that eliminates the error.
Any ideas on associating the two?

In my New sub, I'd like to go ahead and populate the primary combo:

    Public Sub New()
        MyBase.Width = 145
        PopulatePrimaryCbo(Me)
    End Sub

But how to 'test' that it's not the secondary combo, since both will run the New() sub?
Dim cboPrimary, cboSecondary as CustomCombo

I can open a new question if this takes this one too far off course...
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Accepted Solution

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jcoehoorn earned 250 total points
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I'd have something like this in the class:

    Private ParentBox As CustomCombo = Nothing

    Public Sub New(Optional ByRef Parent As CustomCombo = Nothing)
        MyBase.Width = 145
   
        If Parent Is Nothing Then
             PopulatePrimaryCbo(Me)
        Else
             ParentBox = Parent
        End If
    End Sub

Then if ParentBox is nothing, you know you are the parent.  Otherwise you have a reference to the parent already handy.  Also, you may want to make PopulatePrimaryCbo() a member of the new control.  Just have a public method called 'Populate()' that you can call from your main code, and perhaps pass a database connection to if needed.
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Author Comment

by:sirbounty
Comment Utility
So, I set the Parent property like so:?

   Dim cboCat, cboSub As New CustomCombo
   cboCat.Parent = cboCat

If that's the case, I should remove the test for Parent from New(), and just run the public populate sub after setting the Parent property (I think)?
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Expert Comment

by:jcoehoorn
Comment Utility
Dim cboCat As New CustomCombo()
Dim cboSub As New CustomCombo(cboCat)
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Author Comment

by:sirbounty
Comment Utility
Ah - I missed the optional signature...thanx!
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