ContentPageBase

// 1
public abstract class ContentPageBase<TViewModel> : ReactiveContentPage<TViewModel> where TViewModel : ViewModels.ViewModelBase<TViewModel>
{    
    // 2
    protected Lazy<CompositeDisposable> ControlBindings = new Lazy<CompositeDisposable>(() => new CompositeDisposable()); 

    // 3
    bool _controlsBound = false;

    // 4
    protected abstract void SetupUserInterface();

    protected abstract void BindControls();

    // 5
    protected ContentPageBase() : base()
    {   
        SetupUserInterface();
    }

    //8
    const string RendererPropertyName = "Renderer";

    protected override void OnPropertyChanged(string propertyName = null)
    {
        base.OnPropertyChanged(propertyName);

        if (propertyName.Equals(RendererPropertyName, StringComparison.OrdinalIgnoreCase))
        {
            var rendererResolver = DependencyService.Get<Interfaces.IRendererResolver>();

            if (rendererResolver == null)
                throw new NullReferenceException("The renderer resolver was not initialized properly");

            if (rendererResolver.HasRenderer(this))
                RegisterBindings();
            else
                UnregisterBindings();
        } 
    }

    //6
    protected void RegisterBindings()
    {
        if (_controlsBound)
            return;

        ViewModel?.RegisterBindings();
        BindControls();
        _controlsBound = true;
    }

    //7
    protected void UnregisterBindings()
    {
        _controlsBound = false;

        ViewModel?.UnregisterBindings();

        if (!ControlBindings.IsValueCreated) return;

        ControlBindings?.Value?.Clear();
    }
}