C#

class TheBase
{
  public event EventHandler MyEvent;
 
  protected virtual void OnMyEvent(EventArgs e)
  {
    if( MyEvent != null )
    {
      MyEvent(this, e);
    }
  }
}
 
class TheDerived
{
  protected override void OnMyEvent(EventArgs e)
  {
    if( ShouldFireMyEvent )
    {
      base.OnMyEvent(e);
    }
    else
    {
      // the MyEvent event will not be fired
    }
  }
 
  public void FireMyEvent()
  {
    // CAUTION: Fire MyEvent only if the code using this event is guaranteed
    // not to break because the Event was fired outside of its normal usage.
    //
    // IOW, if several events fire in a sequence, you must fire all of them
    // in that sequence.  Also don't fire this event yourself if you have
    // other means of doing so (such as calling Invalidate in a Windows
    // Forms Control instead of firing the Paint event yourself.)
    OnMyEvent(EventArgs.Empty);
  }
}

foreach (Process p in Process.GetProcesses())
  Console.WriteLine(p.MainWindowTitle);

[DllImport("kernel32", SetLastError=true)]
static extern IntPtr CreateFile(
string filename,
uint desiredAccess,
uint shareMode,
uint attributes,
uint creationDisposition,
uint flagsAndAttributes,
uint templateFile
);

int num = Int32.Parse(s1);
int num = Convert.ToInt32(s1);