Bind button in DataTemplate to command in the form's ViewModel

It's:

{Binding DataContext.FireCommand,
         RelativeSource={RelativeSource AncestorType=ListBox}}

No need to walk up to the root unless you actually change the DataContext along the way, but as the ListBox seems to bind to a property on the main VM this should be enough.

The only thing i recommend reading is the Data Binding Overview, and the Binding class documentation (including its properties).

---

Also here is a short explanation on how bindings are constructed: A binding consists of a source and a Path relative to that source, by default the source is the current DataContext. Sources that can be set explicitly are: Source, ElementName & RelativeSource. Setting any of those will override the DataContext as source.

So if you use a source like RelativeSource and want to access something in the DataContext on that level the DataContext needs to appear in the Path.

This may be considered unrelated by most, but this search is only 1 of 3 results that you'll find searching for data binding commands to controls inside a data template--as it relates to Xamarin Forms. So, maybe it'll help someone now-a-days.

Like me you may wonder how to bind commands inside a BindableLayout. Credit jesulink2514 for answering this at Xamarin Forums, where it's probably overlooked by many because of all the comments. Here's his solution, but I'm including the link below:

<ContenPage x:Name="MainPage">
<ListView Grid.Row="1"
              ItemsSource="{Binding Customers}"
              VerticalOptions="Fill"
              x:Name="ListviewCustomer">
      <ListView.ItemTemplate>
        <DataTemplate>
      <Label Text="{Binding Property}"/>
          <Button Command="{Binding BindingContext.ItemCommand, Source={x:Reference MainPage}}" 
                         CommandParameter="{Binding .}">Click me</Button>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>
</ContentPage>

https://forums.xamarin.com/discussion/comment/217355/#Comment_217355