<TextBlock
                    Text="{Binding}"
                    HorizontalAlignment="Center"
                    VerticalAlignment="Center" />

        public SetTimer() {
            Timer timer = new Timer(timerCallback, null, 0, 1000);
        }

        void timerCallback(object nothing) {
            Deployment.Current.Dispatcher.BeginInvoke(
                () => this.DataContext = DateTime.Now);
        }