How do i use the PropertyChangedMessage of a property annotated with [AlsoBroadcastChange]?

[cleissonalves]

Hi, I am testing the new features of the CommunityToolkit.Mvvm 8.0.0-preview3, and would like to know how to properly make use of the broadcast message generated by the [AlsoBroadcastChange] attribute.

Here is an example:

[ObservableObject]
[ObservableRecipient]
public partial class InputAViewModel
{
	[ObservableProperty]
	[AlsoBroadcastChange]
	private string inputA;
}

[ObservableObject]
[ObservableRecipient]
public partial class InputBViewModel
{
	[ObservableProperty]
	[AlsoBroadcastChange]
	private string inputB;
}

Question:

• How do i detect and receive the broadcasted PropertyChangedMessage sent by the InputA property and set its NewValue to InputB?

[cleissonalves]

For future reference and if someone has the same question, i found two ways to accomplish the desired outcome:

Using the IRecipient interface:

[ObservableObject]
[ObservableRecipient]
public partial class InputBViewModel : IRecipient<PropertyChangedMessage<string>>
{
	[ObservableProperty]
	[AlsoBroadcastChange]
	private string inputB = string.Empty;

	public void Receive(PropertyChangedMessage<string> msg)
	{
		if (msg.Sender.GetType() == typeof(InputAViewModel))
		{
			if (msg.PropertyName == nameof(InputAViewModel.InputA))
				InputB = msg.NewValue;
		}
	}
}

Obs: Multiple IRecipient interfaces can be used, one for each message type to receive and each requiring a Receive method overload for its type. Like this:

[ObservableObject]
[ObservableRecipient]
public partial class InputBViewModel : IRecipient<PropertyChangedMessage<string>>, IRecipient<PropertyChangedMessage<int>>
{
	[ObservableProperty]
	[AlsoBroadcastChange]
	private string inputB = string.Empty;

	public void Receive(PropertyChangedMessage<string> msg)
	{
		//do something with message string value
	}

	public void Receive(PropertyChangedMessage<int> msg)
	{
		//do something with message int value
	}
}

The second way requires writing the constructor and the OnActivate method so they wont be generated by default, and each message has to be registered manually:

[ObservableObject]
[ObservableRecipient]
public partial class InputBViewModel
{
	[ObservableProperty]
	[AlsoBroadcastChange]
	private string inputB = string.Empty;

	public InputBViewModel()
	{
		Messenger = WeakReferenceMessenger.Default;
		IsActive = true;
	}

	protected virtual partial void OnActivated()
	{
		Messenger.Register<PropertyChangedMessage<string>>(this, (obj, msg) => Receive(msg));
		Messenger.Register<PropertyChangedMessage<int>>(this, (obj, msg) => ReceiveNumber(msg));
	}

	public void Receive(PropertyChangedMessage<string> msg)
	{
		//do something with message string value
	}

	public void ReceiveNumber(PropertyChangedMessage<int> msg)
	{
		//do something with message int value
	}
}

[echoix]

Again for future reference, [AlsoBroadcastChange] was changed for [NotifyPropertyChangeRecipients] when changing from 8.0.0-preview3 to 8.0.0-preview4 in #288, so before the first 8.0.0 release.

[mwpowellhtx]

I do not find NotifyPropertyChangedForAttribute in the latest production package. Will this be published soon? Thank you.