C#

public void SetText(ref Label myLabel, string text)
{
   myLabel.Text = text;
}

// CommonObjects class library

namespace CommonObjects
{
    public delegate void UpdateText(string text);
}

// BusinessLayer class library, references CommonObjects

using CommonObjects;

namespace BusinessLayer
{
    public class Strings
    {
        public static void RequestUpdateText(UpdateText updateText)
        {
            updateText.Invoke("New Text");
        }
    }
}

// Presentation layer - a winforms app here with a TextBox (textBox) on the main form (FormMain instance),
// references CommonObjects

using System.Windows.Forms;
using CommonObjects;

public partial class FormMain : Form
{
    public FormMain()
    {
        InitializeComponent();
        RequestUpdateFromClassLibrary();
    }

    private void RequestUpdateFromClassLibrary()
    {
        BusinessLayer.Strings.RequestUpdateText(new UpdateText(UpdateTextBox));
    }
    private void UpdateTextBox(string text)
    {
        textBox.Text = text;
    }
}

private Form MyAppForm;
//
private void Form1_Load(object sender, EventArgs e)
{
    Form MyAppFrm = new Form();
    MyAppFrm.Closing += new CancelEventHandler(MyAppFrm_Closing);
}