How can I bind directly to a child viewmodel?

Question

The goal would be to directly access properties in the child ViewModel without losing the context of the entire ViewModel structure.

Currently, I have a resource in a dictionary that holds a reference to a ViewModel that I use as the data context for the whole application.

So, my datacontext for every view looks like this:

DataContext="{StaticResource mainViewModel}"

In my ViewModel I have nested child ViewModels like so:

public class ParentViewModel {
    public ChildVM ChildVM { get; set; }
    public ParentVM(){
        ChildVM = new ChildViewModel();
    }
}

public class ChildViewModel {
    public string SomeProperty { get; set; }
}

In my view, I can access properties from the data context like so:

<Button Text="{Binding ChildVM.SomeProperty}"/>

But this gets very repetitive. I would like to be able to do:

<Button Text="{Binding SomeProperty}"/>

With my datacontext set to something like this pseudo:

DataContext="{StaticResource MainViewModel, Path=ParentVM.ChildVM}"

Any ideas?

Answer 1

You can change DataContext for group of controls

<!-- DataContext is ParentViewModel -->
<Grid>
   <!-- change DataContext to ChildViewModel -->
   <Grid DataContext="{Binding Path=ChildVM}">
      <Button Content="{Binding SomeProperty}"/>
      <Button Content="{Binding AnotherChildProperty}"/>
   </Grid>
</Grid>

Answer 2

You can set the DataContext on those controls' common parent like dkozl suggests. But if that sub visual tree is relatively large, you should probably consider making a UserControl dedicated to your childVM:

<Grid>
    <ChildControl DataContext={Binding ChildVM}/>
</Grid>

<UserControl x:Class="ChildControl">
    <Grid>
      <Button Content="{Binding SomeProperty}"/>
      <Button Content="{Binding AnotherChildProperty}"/>
   </Grid>
</UserControl>