Use .Net event system : Event System : GUI Windows Forms C# Examples

    
using  System;

public  class  SalaryEvent  :  EventArgs
{
    public  string  Message;

    public  SalaryEvent(string  message)
    {
        this.Message  =  message;
    }
}

public  class  Employee
{
    private  int  salary;

    public  delegate  void  SalaryTaxEventHandler(  object  reactor,  SalaryEvent  myEvent  );

    public  event  SalaryTaxEventHandler  OnTax;

    public  int  Salary
    {
        set
        {
            salary  =  value;

            if  (salary  >  1000)
            {
                SalaryEvent  myEvent  =  new  SalaryEvent("Employee  meltdown  in  progress!");
                OnTax(this,  myEvent);
            }
        }
    }
}

public  class  EmployeeMonitor
{
    public  EmployeeMonitor(Employee  myEmployee)
    {
        myEmployee.OnTax  +=  new  Employee.SalaryTaxEventHandler(DisplayMessage);
    }

    public  void  DisplayMessage(  object  myEmployee,  SalaryEvent  myEvent  )
    {
        Console.WriteLine(myEvent.Message);
    }
}


class  MainClass
{
    public  static  void  Main()
    {
        Employee  myEmployee  =  new  Employee();
        EmployeeMonitor  myEmployeeMonitor  =  new  EmployeeMonitor(myEmployee);

        myEmployee.Salary  =  100;
        myEmployee.Salary  =  500;
        myEmployee.Salary  =  2000;
    }
}