DataGridViewComboBoxColumn Error (Object reference not set to an instance of an object)

Posted on 2007-07-29
Medium Priority
Last Modified: 2012-06-21
VB 2005, Windows Forms

Here is my code:

        Dim nColCombo1 As New DataGridViewComboBoxColumn
        With nColCombo1
            .HeaderText = "Item"
            .Name = "Col_ItemID"
            Dim x As String = MyItem.FillItemsGrid(nColCombo1) ' Rise Error
        End With

In my class :

   Public Function FillItemsGrid(ByRef cBox As Object, Optional ByVal ProvId As Integer = 0) As String
        Dim Sqls As String

My Problem is the error was rised when calling the function ( Object reference not set to an instance of an object . )

Thanx in advance
Question by:hatem72
  • 3
  • 2

Expert Comment

ID: 19588417
I think your problem might be with passing a reference type (object) by reference. Almost always an object should be passed by the default ByVal. You will still be able to change the properties of the object, since ByVal passes a copy of the pointer to the object and not the actual pointer to the object (for reference types such as objects). The danger of passing the original pointer to the object, (ByRef) if not needed is that the method can replace the object with a different instance, which is what I think may be happening.

Author Comment

ID: 19588435

First thank u ... i did try to change ByRef -> ByVal   BUT Same Problem

ok is there any way to pass DataGridViewComboBoxColumn to Class ???
instead of my way
LVL 34

Accepted Solution

Sancler earned 1600 total points
ID: 19588456
I assume MyItem is declared AND instantiated?  E,g, Dim MyItem As New MyClass.  And within scope for the code you show.

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Author Comment

ID: 19588463

Yes Sancler ... MyItem class works fine and there is many functions and subs and all works fine.

Assisted Solution

lorelogic earned 400 total points
ID: 19588476
Your way should work. Just add an includes for the System.Wihdows.Forms  to give access to the DataGridViewComboBoxColumn and type your cbox as that, then use the object passed, even ByVal, the members can be accessed on the original object, so you can populate it.

Author Comment

ID: 19588497


Sancler u r right about the problem ... i am sure that is the class is fine but i dont know
how do i miss the NEW keyword ... after ur post i copy the function form the class
to the form and it works ... so i found where the problem is .

lorelogic thank u for ur help ... SORYY there is just 500p to split .

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