MVVMLIGHT Messaging - Opening Second Window & Returning Result

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WPF

MVVM

Hi,

I'm trying to learn MVVMLIGHT, and using a simple wpf application with the below scenario.
1. My Main page has a ListBox bound to PreCreated employees.
2. When I click a button on the main page (button bound to AddEmployeeCommand, i'd like to open the Second window, which will have text boxes for creating a new employee.
3. When I click Add employee button on the second window, I want it to return that newly created employee to MainWindow.

My purpose here is to understand how Main window activates second window, and second window executes a callback to return the newly created employee.

Note: I have seen Laurent's videos of Messaging and have the sample code, but just not able to create the simple example above. Wanna know where i'm going wrong.

Here's the code I have right now:
MainVewModel

public class MainViewModel : ViewModelBase
    {
        
        private readonly IEmployeeService _employeeService;
        private ObservableCollection<Employee> _employees;

        public MainViewModel(IEmployeeService employeeService)
        {
            _employeeService = employeeService;

            // get employee data for binding to view
            _employeeService.GetEmployees((listOfEmployees, error) =>
                {
                    if (error != null)
                    {
                        // report error here
                        return;
                    }
                    else
                    {
                        _employees = new ObservableCollection<Employee>(listOfEmployees);
                    }
                });
        }

        public ObservableCollection<Employee> Employees
        {
            get { return _employees; }
        }

        public RelayCommand AddEmployeeCommand
        {
            get
            {
                return new RelayCommand(() => {
                    Messenger.Default.Send(new NotificationMessageAction<Employee>("Add new employee", NewEmployeeAdded));
                });
            }
        }

        private void NewEmployeeAdded(Employee newEmployee)
        {
            // When new employee is added
            _employees.Add(newEmployee);
            RaisePropertyChanged("Employees");
        }


                    
    }

SecondVewModel:

public class SecondViewModel : ViewModelBase
    {
        private NotificationMessageAction _newEmployee;

        public SecondViewModel()
        {
            Messenger.Default.Register<NotificationMessageAction<Employee>>(this,
                emp =>
                    {
                        var secondWidnow = new SecondWindow();
                        secondWidnow.Show();
                    });
        }

        private string _name;
        public string Name
        {
            get { return _name; }
            set
            {
                if (_name == value)
                    return;
                else
                {
                    _name = value;
                    RaisePropertyChanged("Name");
                }
            }
        }

        private string _department;
        public string Department
        {
            get { return _department; }
            set
            {
                if (_department == value)
                    return;
                else
                {
                    _department = value;
                    RaisePropertyChanged("Department");
                }
            }
        }

        private string _email;
        public string Email
        {
            get{return _email;}
            set
            {
                if (_email == value)
                    return;
                else
                {
                    _email = value;
                    RaisePropertyChanged("Email");
                }
            }
        }


        public RelayCommand AddEmployeeCommand
        {
            get
            {
                return new RelayCommand(() =>
                {
                    var employee = new Employee
                    {
                        Name = _name,
                        Department = _department,
                        Email = _email
                    };
                    _newEmployee.Execute(employee);
                });
            }
        }

    }

If anyone can point me in the right direction, it would be great.
I'll include the code with this question.

Note: Also, if someone can tell me what message would be the right one for this kind, that would be helpful. I tried to use NotificationMessageAction<employee> since I wanted main window to get back the newly created employee.