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MDI Parent & Child in VB.NET

dbote
dbote asked
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Last Modified: 2012-05-07
I have a MDI Application with a toolbar on the parent form.  This toolbar has the standard buttons, New, Save.  When I click the save button the values returned from controls on the child form are blank.  Example. txtName.text has a value but it is returning a null back to the routine in the parent form.

I have also tried using DirectCast(frmName,form) to run a routine from the child form but it still gives blank values for the controls.

What is the proper way to use the MDI Parent toolbar for child forms?  Specifically the Save control.  

Thank you,

David
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Mike TomlinsonHigh School Computer Science, Computer Applications, Digital Design, and Mathematics Teacher
CERTIFIED EXPERT
Top Expert 2009

Commented:
When the toolbar buttons are clicked in the MdiParent form, you can get the active MdiChild with ActiveMdiChild():
http://msdn.microsoft.com/en-us/library/system.windows.forms.form.activemdichild.aspx

Author

Commented:
I am not having trouble getting the active form.  The save routine is being called by the button on the MDI Parent and the controls with the data are on the MDI  Child.  The data being saved always returns a null value because the call starts from the MDI Parent.

If I move the save button to the MDI child everything is fine but that is not how a MDI application "should" work.

What is the best practice for interacting and saving data in an MDI Child form?  There is a lot of info out there about public variables but that just does not seem like the proper way to do it in .NET.

Author

Commented:
Having never done an MDI application in VB.NET I was uncertain how to communicate the data changes between the the parent and child forms.  Now that I have done some experimentation it is very easy.  Of course, I still do not know if this is the MDI standard way but this seems to work very well.

In my child form I create a Sub New for the form like below:

Public Sub New(byVal ClassName as Type)
   Me.InitializeComponent()
   retClass = ClassName    'retClass is a form level variable to HOLD the class info while the form is open
End Sub

In the parent form to call the child do something like this....

        Dim frmNewForm As New frmChildFormName(ClassNameToPass)
        frmNewForm.MdiParent = Me
        modShoulder = frmNewForm.show()

On the child form update the returning class periodically, whenever your application data changes.  The class on the parent form now reflects the changes.  No global variables necessary!

I don't think I left anything out and I may have made a typo but it works well for me.  I think the trick is realizing that forms are classes too and you can add more than the default functions and methods.

dbote




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Mike TomlinsonHigh School Computer Science, Computer Applications, Digital Design, and Mathematics Teacher
CERTIFIED EXPERT
Top Expert 2009

Commented:
There are MANY, MANY ways to go about it...and we can't really say what approach is "best" for your situation as we really don't have info about your application.

If you've found a solution that works then great!

Author

Commented:
So there really is not "best practice" for the exchange of data between MDI Parent and MDI Child forms?
Mike TomlinsonHigh School Computer Science, Computer Applications, Digital Design, and Mathematics Teacher
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Top Expert 2009
Commented:
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Commented:
Thank you for the discussion points.
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