Triggering function on Xamarin.Forms Entry Focused/Unfocused - xamarin.ios

Question

Original problem: I want to call a function each time the soft keyboard is shown/hidden on my Xamarin.Forms ContentPage.
One option was to use a custom renderer where I have access to the keyboard observers. I haven't tried this yet; I thought I'd try banging my head with other approaches first.
Approach 1) Assign event handler to the Focused/Unfocused events of all entries on my page which trigger a keyboard show/hide, in the page's code-behind as follows:
EventHandler<FocusEventArgs> keyboard_handler = (object sender, FocusEventArgs e) =>
{
var binding_context = BindingContext as MyViewModel;
binding_context?.OnKeyboardShowing();
};
PasswordEntry.Focused += keyboard_handler; // doesn't trigger keyboard_handler
PasswordEntry.Unfocused += keyboard_handler; // doesn't trigger
UsernameEntry.Focused += keyboard_handler; // triggers
UsernameEntry.Unfocused += keyboard_handler; //doesn't trigger
Question 1: Why don't some of those trigger?
Approach 2) Use EventTriggers along with a custom TriggerAction<Entry> class, as follows:
Part of the XAML file showing one of the entries (which is in a grid, in a StackLayout in a ScrollView in a Grid, if you must know):
<Entry Grid.Row="0"
x:Name="UsernameEntry"
Margin="0,2"
HorizontalOptions="FillAndExpand"
Placeholder="User"
IsVisible="{Binding UsernameEnabled}"
Completed="Username_Completed"
IsEnabled="{Binding EnableControls}"
Text="{Binding Username, Mode=TwoWay}" >
<Entry.Triggers>
<EventTrigger Event="Focused">
<local:FocusedAction />
</EventTrigger>
</Entry.Triggers>
</Entry>
And the TriggerAction<Entry> class defined in the code-behind:
public class FocusedAction : TriggerAction<Entry>
{
protected override void Invoke(Entry entry)
{
Debug.WriteLine("Reached"); // Except it never reaches here.
}
}
Question 2: Why doesn't Invoke up there ever get triggered?
Am I missing something in my XAML, code-behind or somewhere else? I've checked the Xamarin docs, but as always, I've found them less than useless.