How to update form control from an embedded form

[sohaib_a]

ok..so should it be something like this in child class.. In child form... Public Class1 Public Event addtolist (Byval s as string) '' s is what is to printed in the listbox in parent class ' Private sub() dim obj as new class1 addhandler obj.addtolist,address of class2.addtolistbox ' some code ' ' RaiseEvent addtolist(s) 'where i want to add to the listbox in parent form ' ' End Sub End Class1 In parent form..... public class2 public sub addtolistbox(ByVal sender As Object, _ ByVal e As System.EventArgs) listbox1.items.add(e.argument) end sub end class2 Is this how what you mean Dave? EliottA,thanks for the comments and links.they were useful

[Dave Kreskowiak]

OK, last time... The CHILD form exposes the public Event and calls RaiseEvent when it needs a subscriber to know of a change. This much you got right. The child form does NOT use AddHandler and RemoveHandler on it's own events because it's not subscribing to itself. The PARENT form needs to call AddHandler to subscribe to the events exposed by the child form. But, it can only do this if the parent form has a method that matches the header exposed by the event AND has an child form object (an instance of a class is called an "object"). So, after your parent form creates a child form object, it calls AddHandler to wire up the event exposed by the child form object to the method in the parent form that handles the event.

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Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
     2006, 2007, 2008

[Lost User]

Great description, 5.

[sohaib_a]

Thanks for description dave.. ok..so should it be something like this..i am sorry I havent tried it yet because visual studio is on my other laptop that I dont have with me right now..so just doing some research on it..I'll try it as soon as i get have it. In child form... Public Class1 Public Event addtolist (Byval s as string) '' s is what is to printed in the listbox in parent class ' Private sub() ' some code ' ' RaiseEvent addtolist(s) 'where i want to add to the listbox in parent form ' ' End Sub End Class1 In parent form..... public class2 public obj as new class1 addhandler obj.addtolist,addressof addtolistbox public sub addtolistbox(ByVal sender As Object, _ ByVal e As System.EventArgs) listbox1.items.add(e.argument) end sub end class2 Just one thing i didn't get..sorry to bother you.. "it can only do this if the parent form has a method that matches the header exposed by the event",I don't know what you meant by this. Do you mean the method in the parent form that handles the event should have the same name as the event ie; 'addtolist'?

[Dave Kreskowiak]

Yeah, pretty much got it. Except for one thing:

public sub addtolistbox(ByVal sender As Object, _
ByVal e As System.EventArgs)

This is wrong. Like I said, the method signatures have to match. So, you event is defined like this:

Public Event addtolist(ByVal s as string)

so your event handler has to look the same:

Private Sub AddToListbox(ByVal str As String)

You don't have to have the same variable names, just the same types in the same order.

A guide to posting questions on CodeProject[^]
Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
     2006, 2007, 2008

[sohaib_a]

i tried it the way you said but it isn't working. In the parent form, I created on object of the child form and put the AddHandler syntax in the form load sub.

[Dave Kreskowiak]

What do you mean "it isnt' working"? What IS happening? Have you steped through the code using the debugger to see where it's going and what it's doing??

A guide to posting questions on CodeProject[^]
Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
     2006, 2007, 2008

[sohaib_a]

Yes I have done it..when it reaches the RaiseEvent it doesn't go the event handler..it just goes to the next line.

[Dave Kreskowiak]

That would probably be because there is nothing subscribed to the event.

A guide to posting questions on CodeProject[^]
Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
     2006, 2007, 2008

[sohaib_a]

well I have done exactly as you said. This is in the parent form,I have added this in the form load event of the parent form

Dim obj1 As New childform

AddHandler obj1.addtolist, AddressOf addtolistbox

and this is sub that is subscribed to the event..

Private Sub addtolistbox(ByVal str As String)

ListBox1.Items.Add(str)
End Sub

In the child form.... Public Event addtolist(ByVal s As String) and in the sub where I want to add to listbox in parent form, RaiseEvent addtolist(ds1.Tables(0).Rows(0)("Reader_location").ToString & " Connected ")