How can I use WeakReferenceMessenger instead of MessagingCenter in my iOS project?

Question

I get the following message when I use MessagingCenter in my .NET 7.0 iOS project:

[deprecated] class Microsoft.Maui.Controls.MessagingCenter Associates a callback on subscribers with a specific message name. CS0618: 'MessagingCenter' is obsolete: 'We recommend migrating to CommunityToolkit.MVVM.WeakReferenceMessenger: https://www.nuget.org/packages/CommunityToolkit.Mvvm'

In my iOS project:

MyViewController.cs:

using UIKit;
using SharedCode;
using Microsoft.Maui.Controls;

namespace MyProjectiOS
{
    public partial class MyViewController : UIViewController
    {
        private UIImageView LogoImage;

        public MyViewController() : base("MyViewController", null)
        {

        }

        public override void ViewDidLoad()
        {
            View = new UIView();
            View.BackgroundColor = UIColor.White;
            base.ViewDidLoad();

            UIView viewbg = new UIView(new CoreGraphics.CGRect(0, 0, UIScreen.MainScreen.Bounds.Width, UIScreen.MainScreen.Bounds.Height));
            View.AddSubview(viewbg);

            MessagingCenter.Subscribe<Game1>(this, "Hi", (sender) =>
            {
                G_RemoveLogoTestMyView();
            });

            LogoImage = new UIImageView(UIImage.FromBundle("Image"));
            LogoImage.ContentMode = UIViewContentMode.ScaleAspectFit;
            LogoImage.Tag = 1234;
            LogoImage.Frame = new CoreGraphics.CGRect(0, 0, 375, 375);
            viewbg.AddSubview(LogoImage);
            LogoImage.Center = viewbg.Center;
        }

        public void G_RemoveLogoTestMyView()
        {
            //remove image
            var LogoView = View.ViewWithTag(1234);
            if (null != LogoView)
                LogoView.RemoveFromSuperview();
        }

        public override void DidReceiveMemoryWarning()
        {
            base.DidReceiveMemoryWarning();
        }

    }

}

In my SharedCode project, I use the following code to remove LogoImage:

Game1.cs:

#if __IOS__    
    MessagingCenter.Send<Game1>(this, "Hi");

How can I use WeakReferenceMessenger instead of MessagingCenter in my iOS project?

I only want to use WeakReferenceMessenger to remove LogoImage.

Answer 1

Hello,

Firstly, please install CommunityToolkit.Mvvm nugget package.

Then please create a class in your SharedCode project like following code.

public class Game1Message : ValueChangedMessage<Game1>
{    public Game1Message(Game1 game1) : base(game1)
    {
    }
}

Send the message like following code and delete MessagingCenter.Send<Game1>(this, "Hi"); line. Note：Based on your Game1 generic, I send the Game Object for testing.

        Game1 game1= new Game1();
        WeakReferenceMessenger.Default.Send(new Game1Message(game1));

Open ViewDidLoad method, replace MessagingCenter.Subscribe with the following code.

 WeakReferenceMessenger.Default.Register<Game1Message>(this, (r, m) =>
        {
            // Handle the message here, with r being the recipient and m being the 
           // input message. Using the recipient passed as input makes it so that
            // the lambda expression doesn't capture "this", improving performance.
            G_RemoveLogoTestMyView();
        });

Here is a document about Sending and receiving messages

Best Regards,

Leon Lu

---

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