C#

public class FormA
{
   public FormA (ClassB)
  {
     m_ClassB = ClassB;
  }

  private void ClassA_Load ()
  {
    subscribe to ClassB ClosedFormC – routine to call: ClassB_ClosedFormC.
  }

  private void UserSelection_Click()
  {
     m_ClassB.method1();
     If FormCIsOpen 
    {
      Hide();
     }
  }

   ClassB_ClosedFormC()
   {
     Show();
   }
} // end of ClassA


public class ClassB
{
  public void ClassB()
  {
    m_FormCOpen = false;
  }

  public void method1()
  {
    FormC m_FormC = new FormC();
    subscribe to FormC.Closed – method to call FormC_Closed
    m_FormCOpen = true;
    m_FormC.Show();
    do some stuff
  }

  private void FormC_Closed
  {
     trigger ClosedFormC
     m_FormCOpen = false; 
  }

  bool FormCIsOpen
  {
    get
    {
      return m_FormCOpen;
    }
  }
}// end ClassB