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Question on Views and ViewModels

Printed From: IdeaBlade
Category: DevForce
Forum Name: DevForce 2010
Forum Discription: For .NET 4.0
URL: http://www.ideablade.com/forum/forum_posts.asp?TID=2190
Printed Date: 24-Jan-2026 at 4:26am


Topic: Question on Views and ViewModels
Posted By: BillG
Subject: Question on Views and ViewModels
Date Posted: 24-Sep-2010 at 1:16pm
Some people say that you should have one viewmodel per view. But I am wondering if that is always true. For example, you have a SalesInvoiceView which is divided into the upper portion of the form for the header information and the lower portion of the form for the detail lines in a grid. The SalesInoivceViewModel class holds an observablecollection of salesInvoiceLines which fill the grid. Next to the grid is Add/Edit/Delete buttons which pop up a window for the user to enter the detail lines etc in a form called SalesInvoiceLineView. I think that that this view should be passed the parents viewmodel and both views should share it.
 
Can anyone give me a good reason why I need two viewmodels in this case?
 
Bill
 


Replies:
Posted By: Peer
Date Posted: 25-Sep-2010 at 12:07pm
Hi Bill,
I'm wondering about the same issue ( http://www.ideablade.com/forum/forum_posts.asp?TID=2189&PID=8621#8621 - http://www.ideablade.com/forum/forum_posts.asp?TID=2189&PID=8621#8621 ) and in my own words:

I think the viewmodel acts like  a businessprocess container with all the possible actions for a certain businessprocess. Additonally you add enough commands and navigation handles to let the view interact with the viewmodel.

Your Invoice screen handles the businessprocess "SalesInvoices" so in my opinion you should have ha viewmodel "SalesInvoiceViewModel" which contains all the entities , logic, validationrules ?? navigation (next,prev) and so on.

When I'm wrong, please let me know :)
Peer

Posted By: BillG
Date Posted: 25-Sep-2010 at 12:23pm
I agree. The SaleInvoiceView should have a SalesInvoiceViewModel but does the SalesInvoiceLineView need a separate ViewModel or can it share the SalesInvoiceViewModel since the SalesInvoiceLineView is a child view of the SalesInvoiceView and can't exist without it.
 
Bill
 


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