(Library Part 5) Extending Control Behavior with Button

public partial class LabelBase
{
    public LabelBase()
    {
        InitializeComponent();
    }

    // All properties: View, IsRequired, Label, Info, Error, ShowLoader, etc.
    
    public static readonly BindableProperty ActionIconSourceProperty = 
        BindableProperty.Create(nameof(ActionIconSource), typeof(ImageSource), 
        typeof(LabelBase), defaultValue: null, propertyChanged: ActionIconSourceChanged);

    public ImageSource? ActionIconSource
    {
        get => (ImageSource?)GetValue(ActionIconSourceProperty);
        set => SetValue(ActionIconSourceProperty, value);
    }

    public static readonly BindableProperty ActionIconCommandProperty = 
        BindableProperty.Create(nameof(ActionIconCommand), typeof(ICommand), 
        typeof(LabelBase), defaultValue: null, propertyChanged: ActionIconCommandChanged);

    public ICommand? ActionIconCommand
    {
        get => (ICommand?)GetValue(ActionIconCommandProperty);
        set => SetValue(ActionIconCommandProperty, value);
    }

    // All changed methods: ElementChanged, IsRequiredChanged, LabelChanged,
    // InfoChanged, ErrorChanged, ShowLoaderChanged, etc.

    private static void ActionIconSourceChanged
        (BindableObject bindable, object oldValue, object newValue) 
            => ((LabelBase)bindable).UpdateActionIconSourceView();
    private static void ActionIconCommandChanged
        (BindableObject bindable, object oldValue, object newValue) 
            => ((LabelBase)bindable).UpdateActionIconCommandView();

    // All UpdateView methods: UpdateElementView, UpdateIsRequiredView, UpdateLabelView,
    // UpdateInfoView, UpdateErrorView, UpdateShowLoaderView, etc.

    private void UpdateActionIconSourceView()
    {
        // The button is visible only if we define a picture image.
        ActionIconButton.IsVisible = ActionIconSource is not null;
        ActionIconButton.Source = ActionIconSource;
    }

    private void UpdateActionIconCommandView()
    {
        ActionIconButton.Command = ActionIconCommand;
    }
}

public partial class PickerPopupLabel
{
    private CollectionPopup? _collectionPopup;
    private readonly TapGestureRecognizer _tapGestureRecognizer;

    public PickerPopupLabel()
    {
        InitializeComponent();
        
        _tapGestureRecognizer = new TapGestureRecognizer();
        _tapGestureRecognizer.Tapped += OnTapped;

        GestureRecognizers.Add(_tapGestureRecognizer);
    }
    
    private void OnTapped(object? sender, EventArgs e)
    {
        _collectionPopup = new CollectionPopup
        {
            BindingContext = this,
            Title = !string.IsNullOrEmpty(Title) ? Title : Label,
            ItemsSource = ItemsSource,
            SelectedItem = SelectedItem,
            ItemDisplay = ItemDisplay,
        };

        _collectionPopup.SetBinding(CollectionPopup.SelectedItemProperty, "SelectedItem");
        _collectionPopup.SetBinding(CollectionPopup.ItemsSourceProperty, "ItemsSource");

        Shell.Current.ShowPopup(_collectionPopup);
    }
    
    protected override void OnBindingContextChanged()
    {
        base.OnBindingContextChanged();

        // Display default image if ActionIconSource is null.
        ActionIconSource ??= "chevron_bottom.png";
        // Add the action to display the CollectionPopup if ActionIconCommand is null.
        ActionIconCommand ??= new Command(() => OnTapped(null, EventArgs.Empty));
    }

    // The rest of the code: properties, methods.
}

public partial class LabelBase
{
    /// ...
    private void UpdateShowLoaderView()
    {
        LoaderActivityIndicator.IsVisible = ShowLoader;
        
        if (ActionIconSource is not null)
        {
            // Hide the ActionIconButton when the Loader is visible
            ActionIconButton.IsVisible = !ShowLoader;
        }
    }
    /// ...
}

Microsoft.Maui.Controls.Application.Current!.MainPage!
    .DisplayAlert(title, message, accept);

public class DisplayService : IDisplayService
{
    public Task ShowPopupAsync(string title, string message, string accept = "OK")
    {
        return Microsoft.Maui.Controls.Application.Current!.MainPage!
            .DisplayAlert(title, message, accept);
    }
}

public static class DependencyInjection
{
    public static IServiceCollection AddInfrastructure(this IServiceCollection services)
    {
        services.AddSingleton<INavigationService, NavigationService>();
        services.AddSingleton<IToastService, ToastService>();
        services.AddSingleton<IDisplayService, DisplayService>();
        
        return services;
    }
}

public partial class EntryPageViewModel : ViewModelBase
{
    private readonly ILogger<EntryPageViewModel> _logger;
    private readonly IToastService _toastService;    
    private readonly IDisplayService _displayService;
    
    public EntryPageViewModel(
        ILogger<EntryPageViewModel> logger,
        IToastService toastService,
        IDisplayService displayService)    
    {
        _logger = logger;
        _toastService = toastService;
        _displayService = displayService;

        _logger.LogInformation("Building EntryPageViewModel");
    }

     // Don't show Properties and Methods.
    
    [RelayCommand]
    private async Task FullnameInfo()
    {
        _logger.LogInformation("FullnameInfo()");

        await _displayService.ShowPopupAsync("Full name", 
            "Your first name and last name are used for communication purpose.");
    }
}