How to establish communication/pass data between two ViewModels

Question

I\'m aware this question has already been asked numerous times, and I\'ve read many answers referring to it. Nevertheless, none of them fulfilled my requirements, and hence

Answer 1

Personally I would go with option 3.

The messaging mechanism keeps your viewmodels separated from each other and once you work through one example, you'll see it is quite easy.

Personally I like to add a message broker class with static methods for each message type I want to send, this helps me centralise changes - but essentially you've got a send and receive. You can send what you want and if something wants to receive it they can.

MVVM Light is a great framework for this.

Send:

GalaSoft.MvvmLight.Messaging.Messenger.Send<LoginSuccessMessage>(new LoginSuccessMessage() { UserName = user });

Receive, in my target View Model constructor:

this.MessengerInstance.Register<LoginSuccessMessage>(this, this.OnLoginSuccessMessage);

Handler in the target View Model:

    private async void OnLoginSuccessMessage(LoginSuccessMessage message)
    {
        this.CurrentUserName = message.UserName;
        this.MoveToState(ApplicationViewModelState.Active);

        await Task.Delay(5000);
        this.MoveToState(ApplicationViewModelState.Idle);
    }

In this example, I am sending a user ID as a property on the message class:

public class LoginSuccessMessage : MessageBase
{

    private string _UserName;

    public string UserName
    {
        get
        {
            return this._UserName;
        }

        set
        {
            this._UserName = value;
        }
    }
}

Replace that property with whatever you want be that a collection or complex object.