How to register service with platform code and use it?

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IgorKravchenko-7896 asked May 4, '22 LeonLu-MSFT edited May 5, '22

How to register service with platform code and use it?

I need to show material alert dialog. I have created implementation and want to use it in any place of my code.
I know that in MAUI we can register class: builder.Services.AddSingleton(typeof(IDialogService), typeof(DialogService));
How to use this instead of injecting in constructor? Because I prefer viewModels with empty constructors.
For example like in Xamarin Forms: DependencyService.Get<IDialogService>();
In blazor we can write something like @inject IDialogService DialogService

I remember in Xamarin Forms creating singleton class is popular solution:

 public class MenuService : IMenuService
     {
         private static Lazy<IMenuService> _instance = new Lazy<IMenuService>(() => new MenuService(), System.Threading.LazyThreadSafetyMode.PublicationOnly);
    
         public static IMenuService Instance => _instance.Value;
    
         public Task<string> ShowMenu(View view, string[] items) =>
             DependencyService.Get<IMenuService>().ShowMenu(view, items);
     }

I want to create something similar to this approach for my maui service. How to do this properly?
My implementation:

 public interface IDialogService
     {
         Task<string> ShowDialog(string title, string message, string accept, string cancel, string neutral);
         Task<bool> ShowDialog(string title, string message, string accept, string cancel);
     }
    
     public partial class DialogService : IDialogService
     {
         public partial Task<string> ShowDialog(string title, string message, string accept, string cancel, string neutral);
         public partial Task<bool> ShowDialog(string title, string message, string accept, string cancel);
     }

Android implementation:

 public partial class DialogService : IDialogService
     {
         static Context context;
         internal static Context Context
         {
             get
             {
                 var page = Application.Current.MainPage;
                 var renderer = page.GetRenderer();
    
                 if (renderer?.View.Context != null)
                     context = renderer.View.Context;
    
                 return renderer?.View.Context ?? context ?? throw new NullReferenceException($"{nameof(Context)} cannot be null");
             }
         }
    
         private ISpanned FromHtml(string message)
         {
             if (Build.VERSION.SdkInt >= BuildVersionCodes.N)
                 return Html.FromHtml(message, FromHtmlOptions.ModeLegacy);
             return Html.FromHtml(message);
         }
    
         public partial Task<string> ShowDialog(string title, string message, string accept, string cancel, string neutral)
         {
             TaskCompletionSource<string> taskCompletionSource = new TaskCompletionSource<string>();
             MaterialAlertDialogBuilder alertBuilder = new MaterialAlertDialogBuilder(Context);
             alertBuilder
                 .SetTitle(title)
                 .SetMessage(FromHtml(message))
                 .SetPositiveButton(accept, (sender, args) => taskCompletionSource.SetResult(accept));
             if (cancel != null)
                 alertBuilder.SetNegativeButton(cancel, (sender, args) => taskCompletionSource.SetResult(cancel));
             if (neutral != null)
                 alertBuilder.SetNeutralButton(neutral, (sender, args) => taskCompletionSource.SetResult(neutral));
             AndroidX.AppCompat.App.AlertDialog dialog = alertBuilder.Create();
             dialog.CancelEvent += (object sender, EventArgs e) => taskCompletionSource?.SetResult(null);
             dialog.Show();
             return taskCompletionSource.Task;
         }
    
         public partial Task<bool> ShowDialog(string title, string message, string accept, string cancel)
         {
             TaskCompletionSource<bool> taskCompletionSource = new TaskCompletionSource<bool>();
             MaterialAlertDialogBuilder alertBuilder = new MaterialAlertDialogBuilder(Context);
             alertBuilder
                 .SetTitle(title)
                 .SetMessage(FromHtml(message))
                 .SetPositiveButton(accept, (sender, args) => taskCompletionSource.SetResult(true))
                 .SetNegativeButton(cancel, (sender, args) => taskCompletionSource.SetResult(false));
             AndroidX.AppCompat.App.AlertDialog dialog = alertBuilder.Create();
             dialog.CancelEvent += (object sender, EventArgs e) => taskCompletionSource?.SetResult(false);
             dialog.Show();
             return taskCompletionSource.Task;
         }
     }

dotnet-maui

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Answer 1 · 2022-05-05T05:57:27.28Z

LeonLu-MSFT answered May 5, '22 LeonLu-MSFT edited May 5, '22

Hello,

When you want to use this services, It can be invoked from cross-platform code by creating an object instance and invoking its operation like following code.

internal class MyViewModel
{
    public MyViewModel()
    {
     }

    private void PopAlert()
    {
        IDialogService dialogService = new DialogService();
        dialogService.ShowDialog("info", "this is a test dialog", "OK", "NO");
  }
}

Here is article about :Invoke the cross-platform API.

I test your code in my side, I find you need to set Material style, and your code get the empty context, so I change this initialize MaterialAlertDialogBuilder code.

MaterialAlertDialogBuilder alertBuilder = new MaterialAlertDialogBuilder(MainActivity.InStance, Resource.Style.MaterialComponentsAlert);

Add a style in styles.xml.

<resources>
<style name="MaterialComponentsAlert" parent="Theme.MaterialComponents.Dialog.Alert">
</style>
</resources>

Create Instance in the as context in the MainActivity.cs.

...
public class MainActivity : MauiAppCompatActivity
{
//add this property
    public static MainActivity InStance { get; set; }
    protected override void OnCreate(Bundle savedInstanceState){
//set it
        InStance = this;
....

}

Best Regards,

Leon Lu

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IgorKravchenko-7896 · May 05 at 09:45 AM

Thank you.
I don't want to create a new instance of service all time. I have implemented singleton in service.

 public partial class DialogService : IDialogService
     {
         private static Lazy<IDialogService> _instance = new Lazy<IDialogService>(() => new DialogService(), System.Threading.LazyThreadSafetyMode.PublicationOnly);
         public static IDialogService Instance => _instance.Value;
    
         public partial Task<string> ShowDialog(string title, string message, string accept, string cancel, string neutral);
         public partial Task<bool> ShowDialog(string title, string message, string accept, string cancel);
     }

But this doesn't resolve my main problem. Maybe I was non-clear in my post. My main question is how to inject implementation to viewModel with parameterless constructor. Because I want to have possibility to use view models in other projects (winforms, wpf, etc) but need empty constructors. Thanks.

Update: after web surfing I found the thing I need called "property injection". I mean something like this:

 [Inject]
 public IDialogService DialogService { get; set; }

Do we have something built in MAUI or should I use Autofac or something else? Thanks.

0 ·

LeonLu-MSFT IgorKravchenko-7896 · May 05 at 09:52 AM

Do we have something built in MAUI?

No. Autofac is a third part plugin, you can open a issue in Autofac Github page. https://github.com/autofac/Autofac/issues

0 ·

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