我想在运行时检查互联网访问，使用Xamarin Essential我试图实现相同的。但事件没有正确触发。目前，它是击中时，第一次连接丢失。没有响应时，再次在线。请帮助我在这方面。在Android的工作正常，问题是在iOS。
这是我代码。

BaseViewModel: INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    public bool IsNotConnected { get; set; }
    public BaseViewModel()
    {
        Connectivity.ConnectivityChanged += Connectivity_ConnectivityChanged;
        IsNotConnected = Connectivity.NetworkAccess != NetworkAccess.Internet;
    }

    ~BaseViewModel()
    {
        Connectivity.ConnectivityChanged -= Connectivity_ConnectivityChanged;
    }

    void Connectivity_ConnectivityChanged(object sender, ConnectivityChangedEventArgs e)
    {
        IsNotConnected = e.NetworkAccess != NetworkAccess.Internet;
    }
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}