Mvvm strange messenger behaviour

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C#

XAML

WPF

MVVM

I am trying to pass a User between two ViewModels. To do this I am using the MVVM light Messenger framework. Even though a breakpoint is hit where I try to action the model that is passed to the second ViewModel, some TextBlocks that are bound to properties are not updated.

What I have tried:

Here is how I pass the 'User' when someone clicks a login button:

#region Login
private DelegateCommand _loginCommand;
public ICommand LoginCommand
{
    get
    {
        _loginCommand = new DelegateCommand(param => Login());
        return _loginCommand;
    }
}

private async void Login()
{
    var waitWindow = new PleaseWaitWindow();
    waitWindow.Show();

    if (await LoginCheck())
    {
        // TODO: Navigate to the DashboardView
        Messenger.Default.Send(new ChangePage(typeof(DashboardViewModel)));
        Messenger.Default.Send(_chosenUser);
    }

    waitWindow.Close();
}
#endregion

Here is how I subscribe to that message and use its contents:

public DashboardViewModel()
{
    Messenger.Default.Register<User>(this, OnUserReceived);
    Messenger.Default.Register<ChangePage>(this, ChangePage); // Register to Messenger to change Views hosted in ContentControl
}

private void OnUserReceived(User user)
{
    FirstName = user.FirstName; // Breakpoint is hit here with correct value
    LastName = user.LastName;
}

And the two TextBlocks that are bound to the FirstName and LastName properties..:

<StackPanel VerticalAlignment="Center" Margin="5">
    <TextBlock Text="{Binding FirstName}" Foreground="White" Margin="5" FontSize="18"/>
    <TextBlock Text="{Binding LastName}" Foreground="White" FontWeight="Bold" Margin="5" FontSize="20"/>
</StackPanel>

If I set a breakpoint where I action the Messenger then FirstName and LastName are set to the correct values. However, the TextBlocks are not updated and their text remains null.

I have implemented a test button on the DashboardView that simply sets FirstName ="Test"; and this does update the TextBlock to say Text so I am confused as to why passing in a type of User and using its FirstName and LastName doesn't work.

EDIT:

private void OnUserReceived(User user)
{
    Application.Current.Dispatcher.Invoke(() =>
    {
        FirstName = user.FirstName;
        LastName = user.LastName;
    });
}