Azure移动服务频道中出现Null异常

我正在windows phone上学习推送通知教程。开始时，推送通知没有问题

然而，几天后，我打开了编码，发现了这个错误：

System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=UtemFtmkDB
  StackTrace:
       at UtemFtmkDB.MainPage.ButtonSave_Click(Object sender, RoutedEventArgs e)
       at System.Windows.Controls.Primitives.ButtonBase.OnClick()
       at System.Windows.Controls.Button.OnClick()
       at System.Windows.Controls.Primitives.ButtonBase.<OnMouseLeftButtonUp>b__3()
  InnerException: 

---

每当我从

：App.CurrentChannel.ChannelUri.ToString（）检索数据时，我都会收到此错误。为什么？
频道可能尚未达到“已连接”状态

检查：

CurrentChannel.ConnectionStatus == ChannelConnectionStatus.Connected

如果这是真的，那么ChannelUri应该有一个非空值。
您需要连接到ChannelUriUpdated事件：

private void AcquirePushChannel()
{
    CurrentChannel = HttpNotificationChannel.Find("MyPushChannel");

    if(null != CurrentChannel)
    {
        CurrentChannel.ChannelUriUpdated += CurrentChannelOnChannelUriUpdated;        
    }
    else
    {
        CurrentChannel = new HttpNotificationChannel("MyPushChannel");
        CurrentChannel.ChannelUriUpdated += CurrentChannelOnChannelUriUpdated;        

        CurrentChannel.Open();
        CurrentChannel.BindToShellTile();
    }
}

private void CurrentChannelOnChannelUriUpdated(object sender, NotificationChannelUriEventArgs args)
{
    // you can now get the URI from args.ChannelUri
}

请注意，对于现有通道，通道uri也可能会更改。因此，无论是否创建新频道，都应该侦听ChannelUriUpdate事件

private void AcquirePushChannel()
{
    CurrentChannel = HttpNotificationChannel.Find("MyPushChannel");

    if(null != CurrentChannel)
    {
        CurrentChannel.ChannelUriUpdated += CurrentChannelOnChannelUriUpdated;        
    }
    else
    {
        CurrentChannel = new HttpNotificationChannel("MyPushChannel");
        CurrentChannel.ChannelUriUpdated += CurrentChannelOnChannelUriUpdated;        

        CurrentChannel.Open();
        CurrentChannel.BindToShellTile();
    }
}

private void CurrentChannelOnChannelUriUpdated(object sender, NotificationChannelUriEventArgs args)
{
    // you can now get the URI from args.ChannelUri
}