WPF how to expose binding source as a resource - wpf

Question

I have a TabControl located in the ParentView. Inside that TabControl I have ChildView that contains a button with command bound to ParentViewModel's ICommand:
<Button Command="{Binding DataContext.MyCommand, RelativeSource={RelativeSource AncestorType={x:Type local:ParentView}}}"
CommandParameter="{Binding}">
Quite a few of these actually. Is there a way of creating UserControl resource from that RelativeSource and DataContext so I can declare my buttons more like that?:
<Button Command="{Binding MyCommand, Source={StaticResource MyParentsDataContext}}"
CommandParameter="{Binding}">
Edit
What I came up so far is this:
<UserControl.Resources>
<RelativeSource x:Key="Parent" AncestorType="{x:Type local:ParentView}" />
</UserControl.Resources>
<Button Command="{Binding DataContext.MyCommand, RelativeSource={StaticResource Parent}}"
CommandParameter="{Binding}">
Slightly dryer and more readable, but still not sure how to get rid of DataContext if possible at all.

Answer 1

You can put anything you like in application.current.resources.
It's rather like a sort of in memory dictionary with key of string and value of object.
You could therefore add an instance of a class in a resource dictionary merged in app.xaml:
<local:AnyViewModel x:Key="VM"/>
If you need no parameters for this then you may find you never need to change that.
If there's more to this parent viewmodel then you can replace a dummy version.
If you then either merge in an instance from another resource dictionary with the same key in a more local scope or set it in code:
Application.Current.Resources["VM"] = newInstance;
That then would replace what a binding would find in resources.
If you want to do that dynamically then there's a bit of a trick with the dynamicresource to bear in mind.
You'd need:
<Button DataContext="{DynamicResource VM}" Command="{Binding MyCommand}"
CommandParameter="{This is now a complication}">
If the VM doesn't need to be dynamic then you're OK with staticresource:
<Button Command="{Binding MyCommand, Source={StaticResource VM}}"
CommandParameter="{Binding}">
If that isn't convenient for some reason you could make the resource a viewmodel which implements inotifypropertychanged and the specific viewmodel you're interested a property of that:
<Button Command="{Binding ParentViewmodel.MyCommand, Source={StaticResource VM}}"
CommandParameter="{Binding}">
That would allow you to switch out ParentViewmodel on the command.