Question about ViewModel Management (DesignTime Vs Run Time)

Question

I have a fairly basic WPF UI whereby user requests cause a new tab to open in my TabControl. The TabControl is bound to an ObservableCollection

Answer 1

Yes I think it will interfere with your current setup

The ViewModelLocator is a static class that returns a dummy object at design time, and a static ViewModel at runtime. This means that

• The ViewModelLocator, not your ParentViewModel, contains your TabViewModels

• You cannot have multiple instances of the same Tab (ViewModel) open at once

• You cannot manage Open/Closed tabs unless you reference the UserControl, which is a violation of the MVVM principle where the ViewModel doesn't know of the View

• You can't instantiate new copies of the TabViewModel with parameterized constructors. For example, OpenTabs.Add(new CustomerViewModel(CustomerId));

Perhaps an alternative could be a Converter? One that returns a static object if in design time, or the bound object during runtime? I've never tested such a thing but in theory it should work :)

Answer 2

The built in MS stuff is not bad, but another more elegant and structurally sound alternative which I am busy incorporating in my project is: http://msdn.microsoft.com/en-us/magazine/dn169081.aspx

Basically, you use the MVVM Light toolkit with the SimpleIoc container it comes with and end up with the ability to serve up data for the following three scenarios:

Design time, Run time, and Test time.

Better still, the whole point of MVVM Light is to have your stuff be directly editable in Blend and there is a whole series of videos and blogs and sample apps describing it all. I wish I had found these earlier in my WPF explorations.

Answer 3

There is an easier way to do this. Have a DesignTimeUserAdministrationViewModel and populate it with static data in the constructor and refer that in UserControl as:

<UserControl d:DataContext="{d:DesignInstance designTimeVMs:DesignTimeUserAdministrationViewModel, IsDesignTimeCreatable=True}">

This way you have a design time test data bound to d:DataContext and runtime live data bound to the actual DataContext. More details here.