C＃我的活动总是空的......为什么......？

Question

/ *类库 / / calcEventArgs.cs * /

   namespace calc1
   {
       public class calcEventArgs
       {
       }

       public class CalculationCompletedEventArgs : System.EventArgs
       {        
           public string StringValue { get; set; }
           public int IntegerValue { get; set; }
       }
   }

/ * CalcMain.xaml.cs * /

  namespace calc1
   {
       public partial class CalcMain : Page
       {
           public delegate void CalcEventHandler(object sender, CalculationCompletedEventArgs e);
           public event CalcEventHandler CalculateCompletedEvent;

           public CalcMain()
           {
               InitializeComponent();
           }  

           private void Button_Click(object sender, RoutedEventArgs e)
           {
               CalculationCompletedEventArgs pArgs = new CalculationCompletedEventArgs();
               pArgs.StringValue = "1 + 1";
               pArgs.IntegerValue = 2;

               CalcEventHandler eh = CalculateCompletedEvent;
               if (eh != null) eh(this, pArgs);
           }
       }
   }

/ * EventTest应用程序* /

namespace EventTest
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            calc1.CalcMain c = new calc1.CalcMain();
            c.CalculateCompletedEvent += new calc1.CalcMain.CalcEventHandler(CalcfromPage);
        }

        private void CalcfromPage(object sender, calc1.CalculationCompletedEventArgs e)
        {
            MessageBox.Show(e.StringValue + " = " + e.IntegerValue.ToString());
        }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            fraMainScreen.Navigate(new Uri("pack://application:,,,/calc1;component/CalcMain.xaml", UriKind.Absolute));
        }
    }
}

这是我的代码 我有问题 ... CalcEventHandler eh = CalculateCompletedEvent

CalculateCompletedEvent始终为null ..

帮助.. 谢谢。 ^^