Is there any advantage or disadvantage in using a Xamarin.Forms MessagingCenter to communicate between a ViewModel and methods - xamarin

Question

I am looking into using one or other method and in particular method 2. Can anyone tell me the advantages and disadavantages of using the 2nd method over the 1st.
Method 1 - ViewModel.cs
PTBtnCmd = new Command<Templates.WideButton>((btn) =>
MessagingCenter.Send<CFSPageViewModel, Templates.WideButton>(
this, "PTBtn", btn));
Method 1 - MyPage.xaml.cs (SetLang etc.. methods in this file )
MessagingCenter.Subscribe<CFSPageViewModel, Templates.WideButton>(
this, "PTBtn", (s, btn) =>
{
Utils.SetState(btn.Text, vm.PT);
SetLangVisible(btn.Text);
SetLangSelected(btn.Text);
vm.CFSMessage = Settings.cfs.TextLongDescription();
});
or
Method 2 - ViewModel.cs (SetLang etc.. methods in this file )
PTBtnCmd = new Command<string>(SetMode);
private void SetMode(string btnText)
{
Utils.SetState(btnText, PT);
SetLangVisible(btnText);
SetLangSelected(btnText);
CFSMessage = Settings.cfs.TextLongDescription();
}
Would also like to hear comments on the idea of adding methods into the ViewModel.cs code. Would it be better for these to be in another file?

Answer 1

The MessagingCenter
helps you keep your code decoupled. Sometimes you will find yourself in a position
that requires you create a reference between certain code, but by doing so, you have to
compromise on reusability and maintainability.
Try to use it as a last resort; usually there is
another way to achieve your desired functionality. While sending a message can be very
powerful, using it too much can really eat into your readability.
A use case example for MessagingCenter would be a case where you need to update values in multiple
parts of your app. You can subscribe to a message from multiple places and thus execute
code in multiple places when a message is received. Another use case could be if some
background process is done, it can send a message and you can then inform the user in
your UI.

Answer 2

I would not use the messaging in the VM layer because your VM layer can then only be used in Xamarin.Forms. Some Mvm frameworks, like mvvmlight, offer a messaging capability. I would opt for that instead as you could then reuse your VMs in Wpf, Uwp or other UI frameworks other than XF.
Also i wouldn't use the messaging like you have. If probably just use databinding and raise PropertyChanged events in the VM which the view can react to.

Answer 3

To pass data between VMs I'd suggest navigation params or rethinking how you are using this data in general (use some sort of service or dumb down the UI depending on how "fat" your client app must be).
Messaging center as #Andy mentioned would cause reusability issues but this does not mean that you cannot use it. My approach is wrapping it in a separate service and using it in implementation. This will let you to do two things: creating more convenient or better way to use it in accordance to your use case and an option to swap out the implementation of your messenger to any other pub-sub library (or your own impl.) if you will need to use these VMs in WPF project.
Of course using something more universal across platforms would be a great option too but it also depends on how much you are "allowed"/can use third party stuff. At least with MAUI this causes some problems, but this is for another topic.