public AppShell()

{

        InitializeComponent();

Routing.RegisterRoute(nameof(HomePage), typeof(HomePage));

}

[QueryProperty(nameof(User_Name), "username")]

public partial class HomePage : ContentPage

{

    public HomePage()

    {

        InitializeComponent();

    }

    private string user_name;

    public string User_Name

    {

        get { return user_name; }

        set

        {

            user_name = value;

            LblUserName.Text = user_name;

        }

    }

}

  private void Button_Clicked(object sender, EventArgs e)

    {

        Shell.Current.GoToAsync($"{nameof(HomePage)}?username={EntUserName.Text}");

    }