WPF databinding in child control

Question

I am new to WPF. I'm trying to build an application which has a function (call it Initialisation) where a user has to fill in a lot of data and some parts of the form are repeated. We're rewriting a legacy app that has quite a long wizard in although we will probably use collapsible panels in one window rather than next/previous pages. Also some parts are repeated eg the user can specify a number of items, if they say 3 they will need to fill in some configuration info for each, so those controls would need to be repeated three times.

I'm using MVVM and am using this example here: http://msdn.microsoft.com/en-us/magazine/dd419663.aspx

The old wizard had about 4 pages so I'm intending to have one user control (Initialisation) that contains 4 child user controls to break the xaml up a bit.

So far I have the Initialisation (its ViewModel inherits from Workspace ViewModel as in the above example) and it contains one child which is working:

<Expander ExpandDirection="Down" Header="ChildOne">
<view:ChildOne />
</Expander>

I will have separate ViewModels for each child and for Intialisation and this brings me to my problem. The problem I am having is that ChildOne contains a dropdown which I am trying to bind like so:

<ComboBox x:Name="textMessageTypeCmb" ItemsSource="{Binding Path=TextMessageSelectionOptions, Mode=OneTime}"/>

TextMessageSelectionOptions is a public property in ChildOne's ViewModel. This results in no errors but an empty dropdown - that property getter is never called. If I move that property getter code into the Initialisation's ViewModel instead it works but I'm trying to keep my code in manageable chunks so I'd like to put hat code back in ChildOne's ViewModel. It also works if in my MainWindow I create ChildOne as a workspace instead of Initialisation like this

ChildOneViewModel ws = this.Workspaces.FirstOrDefault(vm => vm is ChildOneViewModel) as ChildOneViewModel;

Can anyone advise whether I am taking the right approach (by dividing it up into several user controls) and what I need to do in the binding to make this work? I don't really understand any of this yet especially binding.

Answer 1

It seems to me that your ChildOne view's DataContext is still this Initialisation vm.

You can bind it the views Datacontext to a ChildOneViewModel object

...
<view:ChildOne DataContext={Binding PropertyReturnsChildOneViewModellObject/>
...

or specify the path for the combobox ItemsSource prop.

<ComboBox x:Name="textMessageTypeCmb" ItemsSource="{Binding Path=PropertyReturnsChildOneViewModellObject.TextMessageSelectionOptions, Mode=OneTime}"/>

Note: PropertyReturnsChildOneViewModellObject is a property of the Initialisation vm.