How can I bind a control's command to a child viewmodel command in an MVVM scenario?

Question

I have a window in WPF based upon a viewmodel. The viewmodel includes a child viewmodel that can be switched at runtime. Each child viewmodel has its own commands. The parent view contains a ribbon with buttons that need to bind to the current child viewmodels commands. To switch views I use a content control in the parent view that uses data templates. Each possible child view is a user control that binds to the appropriate viewmodel (that bit works).

    <!-- Switchable area -->
    <ContentControl Content="{Binding ChildViewModel}">
        <ContentControl.Resources>
            <DataTemplate DataType="{x:Type vm:VersionsViewModel}">
                <embeddable:VersionsView />
            </DataTemplate>
            <DataTemplate DataType="{x:Type vm:LockListViewModel}">
                <embeddable:LockListView />
            </DataTemplate>
        </ContentControl.Resources>
    </ContentControl>

So for example, one of my child viewmodels has a refresh command. I want this to appear in the main view in a ribbon button. I've tried setting the binding to the following XAML but it never binds so the command isn't called. What am I doing wrong?

<telerik:RadRibbonButton Size="Large"
                         Text="Refresh"
                         LargeImage="..\Images\Ribbon\32x32\Refresh.png"
                         Command="{Binding ChildView.RefreshCommand}" 
                         telerik:KeyTipService.AccessText="R"/>

Elsewhere in the main view I have bindings for data that comes from the child viewmodel and works fine so I'm really confused! For example, this is the binding I use to get the title for the window.

Title="{Binding ChildViewModel.Title,FallbackValue='My System'}"

The binding of the RibbonButtons Command-property has the Path ChildView.... against what the binding of your Title-property has the Path ChildViewModel.... — Florian Gl
at least you can check the datacontext for your ribbon with Snoop to see what the actual datacontext for your ribbon is. — blindmeis

SteveL SteveL · Accepted Answer · 2013-02-01T14:12:53

<telerik:RadRibbonButton Size="Large"
                         Text="Refresh"
                         LargeImage="..\Images\Ribbon\32x32\Refresh.png"
                         Command="{Binding ChildViewModel.RefreshCommand}" 
                         telerik:KeyTipService.AccessText="R"/>

you weren't binding to the view model

How can I bind a control's command to a child viewmodel command in an MVVM scenario?

1 Answers