Xamarin.Forms Watch Example

WatchPage.xaml

<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:local="clr-namespace:Watch"
    x:Class="Watch.WatchPage">
    <Grid>
        <Grid x:Name="hourBox"
            HorizontalOptions="Center"
            VerticalOptions="Fill">
            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="2*" />
                <RowDefinition Height="3*" />
            </Grid.RowDefinitions>
            <BoxView Color="Black"
                     Grid.Row="1" />
        </Grid>
        <Grid x:Name="minBox"
            HorizontalOptions="Center"
            VerticalOptions="Fill">
            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="*" />
            </Grid.RowDefinitions>
            <BoxView Color="Black" />
        </Grid>
        <Grid x:Name="secBox"
            HorizontalOptions="Center"
            VerticalOptions="Fill">
            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="*" />
            </Grid.RowDefinitions>
            <BoxView Color="Red" />
        </Grid>
    </Grid>
</ContentPage>

WatchPage.xaml.cs

using System;
using Xamarin.Forms;

namespace Watch
{
    public partial class WatchPage : ContentPage
    {
        public WatchPage()
        {
            InitializeComponent();
        }

        protected override void OnAppearing()
        {
            base.OnAppearing();

            UpdateUI(DateTime.Now);

            Device.StartTimer(TimeSpan.FromSeconds(1), () =>
            {
                UpdateUI(DateTime.Now);

                return true;
            });
        }

        void UpdateUI(DateTime time)
        {
            double hour = (time.Hour % 12) / 12.0;
            double min = time.Minute / 60.0;
            double sec = time.Second / 60.0;

            hourBox.Rotation = hour * 360;
            minBox.Rotation = min * 360;
            secBox.Rotation = sec * 360;

            Title = time.ToString("hh:mm:ss");
        }
    }
}