Unable to override OnApplyTemplate - uno-platform

Question

I'm trying to override the NavigationView behavior:
public partial class CustomizableNavigationView : NavigationView
{
public CustomizableNavigationView()
{
// This gets called
}
protected override void OnApplyTemplate()
{
// This doesn't
}
}
It works on UWP, but not on Android. On Android, it doesn't call OnApplyTemplate and the screen remains blank, there's not content. Questions:
Why doesn't OnApplyTemplate get called on Android? I see that here: https://platform.uno/docs/articles/implemented/windows-ui-xaml-frameworkelement.html it says OnApplyTemplate() is on all platforms
There's no error or anything displayed in the Output panne in VS while running with debugger. Should there be any in this case? Do I need to enable something to log errors?
I noticed that if I don't use partial it gaves me error saying partial is required. This is required only on Android, why is that? A more in-depth explanation would help a lot to understand how things work.
Once I figure out why OnApplyTemplate is not called, I want to do this:
base.OnApplyTemplate();
var settingsItem = (NavigationViewItem)GetTemplateChild("SettingsNavPaneItem");
settingsItem.Content = "Custom text";
My hunch is this won't work on Android. Am I correct? :)

Answer 1

Jerome's answer explains why OnApplyTemplate() was not getting called, to address your other questions:
You can configure logging filters for Uno, this is normally defined in App.xaml.cs. Warnings should be logged by default.
The partial is required because Uno does some code-gen behind the scenes to create plumbing methods used by the Xamarin runtime. Specifically because the control is ultimately inheriting from ViewGroup on Android, it's a native object, and requires special constructors that are used only by Xamarin's interop layer. There's some documentation in progress on this.
Try it and see. :) GetTemplateChild() is supported, and setting ContentControl.Content in this way is supported, so I would expect it to work.

Answer 2

At current version (1.45 and below), the application of styles is behaving differently from UWP. We're keeping track of this in this issue.
The gist of the issue is that Uno resolves the style using the current type and not DefaultStyleKey, and cannot find an implicit style for CustomizableNavigationView.
A workaround for this is to either create a named style from the default NavigationView style, or create an implicit style that uses CustomizableNavigationView as the TargetType instead of NavigationView.