windows 8 metro 关于定位

1、概述

• 地理定位的方式有四种：wifi, ip地址, 手机基站, GPS。

• win8内置了wifi, ip地址两种方式，wifi定位的精度在350米左右，ip地址的精度在25千米。

• win8定位服务不提供朝向，高度，速度，地址等数据。

• 当需要用定位服务时，需要显式地提醒用户，并在window8的隐私设置里打开定位服务。

• 在应用能力里打开位置服务。

2、指导方针

• 只调用一次定位的请求，用getGeopostionAsync()方法。

• 设置轨迹数据变化阈值，通过设置MovementThreshold属性，当在此值的范围之外变化时，才触发PositionChanged事件，比如城市间的天气变化。

• 设置位置数据报告频率，通过设置ReportInterval属性，为0时，则实时变化。注意：有些设备设置此属性可能无用。

• 设置精度，通过设置DesiredAccuracy属性，当精度为高时，才会调用GPS。

• 启动延迟，可能会有2秒，注意不要阻塞UI。

• 后台运行，当应用挂起时，数据不会更新，所以考虑后台运行。

• 捕获StatusChanged事件，了解位置服务可用状态。
• 当用户禁止了位置服务时，调用getGeopostionAsync()会报异常，LocationStatus值是disable，这时需要提醒用户去开启位置服务。
• 当状态不可用时，应该清除缓存数据。
• 当用户重新开启位置功能时，不会有任何事件产生，只有依靠程序请求数据来得到这个事件。
• 当应用从挂起到激活时，应当重新获取位置数据。
• 提供一个刷新按钮让用户去重新获取位置数据。
• 建议提示"Your location is currently turned off. Change your settings through the Settings charm to turn it back on.”
• 如果位置不是重要信息，就用通知就行，如果位置是重要信息，比如地图，就用flyout.

3、C#示例

　　获取位置数据

using System;
using System.Collection.Generic;
using System.Linq;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.UI.DirectUI;
using Windows.UI.DirectUI.Controls;
using Windows.UI.DirectUI.Data;
using Windows.Devices.Geolocation;

namespace GeolocationSample
{
    partial class MainPage
    {
        Geolocator geo = null;
        public MainPage()
        {
            InitializeComponent();
        }
        
        private async void button1_Click(
            object sender, RoutedEventArgs e)
        {
            if (geo == null)
            {
                geo = new Geolocator();
            }
            
            IGeoposition pos = await geo.GetGeopositionAsync();            
            textblockLatitude.Text = "Latitude: " + pos.Coordinate.Latitude.ToString();
            textblockLongitude.Text = "Longitude: " + pos.Coordinate.Longitude.ToString();
            textblockAccuracy.Text = "Accuracy: " + pos.Coordinate.Accuracy.ToString();
        }

    }

}

 获取位置变化情况数据

using System;
using System.Collection.Generic;
using System.Linq;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.UI.Core;
using Windows.UI.DirectUI;
using Windows.UI.DirectUI.Controls;
using Windows.UI.DirectUI.Data;
using Windows.Devices.Geolocation;
 
namespace GeolocationEventsSample
{
    partial class MainPage
    {
        private Geolocator geo = null;
        private CoreDispatcher _cd;
 
        public MainPage()
        {
            InitializeComponent();
            _cd = Window.Current.CoreWindow.Dispatcher;
        }
        
        private void button1_Click(object sender, RoutedEventArgs e)
        {
            if (geo == null)
            {
                geo = new Geolocator();
            }
            if (geo != null)
            {
                geo.PositionChanged += 
                    new TypedEventHandler<Geolocator,
                        PositionChangedEventArgs>(geo_PositionChanged);
            }
        }
        
     private void button2_Click(object sender, RoutedEventArgs e)
     {
         if (geo != null)
         {
             geo.PositionChanged -= new TypedEventHandler<Geolocator, PositionChangedEventArgs> (geo_PositionChanged);
         }
     }
       
     private void geo_PositionChanged(Geolocator sender, PositionChangedEventArgs e)
     {
         _cd.InvokeAsync(CoreDispatcherPriority.Normal, (s, a) =>
         {
             IGeoposition pos = (a.Context as IPositionChangedEventArgs).Position;
             textLatitude.Text = "Latitude: " + pos.Coordinate.Latitude.ToString();
             textLongitude.Text = "Longitude: " + pos.Coordinate.Longitude.ToString();
             textAccuracy.Text = "Accuracy: " + pos.Coordinate.Accuracy.ToString();
          }, this, e);
     }
   }
}

设置位置数据变化阈值

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
using Windows.UI.Core;
using Windows.Devices.Geolocation;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238

namespace GeolocationAdjustDistance
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class BlankPage : Page
    {
        private Geolocator geo = null;
        private CoreDispatcher _cd;
        private double prevLatitude = -1;
        private double prevLongitude = -1;
        private double totalDistance = 0;

        public BlankPage()
        {
            this.InitializeComponent();
            _cd = Window.Current.CoreWindow.Dispatcher;
        }

        /// <summary>
        /// Invoked when this page is about to be displayed in a Frame.
        /// </summary>
        /// <param name="e">Event data that describes how this page was reached.  The Parameter
        /// property is typically used to configure the page.</param>
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
        }

        private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            if (geo == null)
            {
                geo = new Geolocator();
            }
            if (geo != null)
            {
                geo.PositionChanged += new TypedEventHandler<Geolocator,
                    PositionChangedEventArgs>(geo_PositionChanged);
                geo.StatusChanged += new TypedEventHandler<Geolocator,
                    StatusChangedEventArgs>(geo_StatusChanged);

                geo.MovementThreshold = float.Parse(tbThreshold.Text);
                tbThreshold.IsEnabled = false;
                TextBox1.Text = "Tracking Started " + 
                                "(Time, Latitude, Longitude, Distance)\n";
            }
        }

        private void Button_Click_2(object sender, RoutedEventArgs e)
        {
            if (geo != null)
            {
                geo.PositionChanged -= new TypedEventHandler<Geolocator,
                    PositionChangedEventArgs>(geo_PositionChanged);
                geo.StatusChanged -= new TypedEventHandler<Geolocator, 
                    StatusChangedEventArgs>(geo_StatusChanged);
                TextBox1.Text += "\nTracking Stopped.\n" +
                                 "Total Distance recorded: " +
                                 totalDistance.ToString("F2") + " m\n";
                tbThreshold.IsEnabled = true;
            }
        }

        private double CalculateDistance(double prevLat, double prevLong, double currLat, double currLong)
        {
            const double degreesToRadians = (Math.PI / 180.0);
            const double earthRadius = 6371; // kilometers

            // convert latitude and longitude values to radians
            var prevRadLat = prevLat * degreesToRadians;
            var prevRadLong = prevLong * degreesToRadians;
            var currRadLat = currLat * degreesToRadians;
            var currRadLong = currLong * degreesToRadians;

            // calculate radian delta between each position.
            var radDeltaLat = currRadLat - prevRadLat;
            var radDeltaLong = currRadLong - prevRadLong;

            // calculate distance
            var expr1 = (Math.Sin(radDeltaLat / 2.0) *
                         Math.Sin(radDeltaLat / 2.0)) +

                        (Math.Cos(prevRadLat) * 
                         Math.Cos(currRadLat) *
                         Math.Sin(radDeltaLong / 2.0) * 
                         Math.Sin(radDeltaLong / 2.0));

            var expr2 = 2.0 * Math.Atan2(Math.Sqrt(expr1), 
                                         Math.Sqrt(1 - expr1));

            var distance = (earthRadius * expr2); 
            return distance * 1000;  // return results as meters
        }

        void geo_PositionChanged(Geolocator sender, PositionChangedEventArgs args)
        {
            _cd.InvokeAsync(CoreDispatcherPriority.Normal, (s, a) =>
            {
                Geoposition pos = (a.Context as IPositionChangedEventArgs).Position;
                double updateDistance = 0;

                // Calculate distance;
                if ( ( prevLatitude == -1 ) || ( prevLongitude == -1 ) ) 
                {
                   updateDistance = 0;
                } else {
                   updateDistance = CalculateDistance( prevLatitude, prevLongitude, 
                      pos.Coordinate.Latitude, pos.Coordinate.Longitude );
                }

               // Update tracking
               prevLatitude = pos.Coordinate.Latitude;
               prevLongitude = pos.Coordinate.Longitude;
               totalDistance += updateDistance;

               // display the results.
               TextBox1.Text += "Position Update: " +
                                pos.Coordinate.Timestamp.ToString("T") + ", " +
                                pos.Coordinate.Latitude.ToString("F3") + ", " +
                                pos.Coordinate.Longitude.ToString("F3") + ", " +
                                updateDistance.ToString("F2") + " m\n";
            }, this, args);
        }

        void geo_StatusChanged(Geolocator sender, StatusChangedEventArgs args)
        {
            var newStatus = args.Status;
            var strStatus = "";

            switch (newStatus)
            {
                case PositionStatus.Ready: 
                    strStatus = "Location is available.";
                    break;
                case PositionStatus.Initializing:
                    strStatus = "Geolocation service is initializing.";
                    break;
                case PositionStatus.NoData:
                    strStatus = "Location service data is not available.";
                    break;

                case PositionStatus.Disabled:
                    strStatus = "Location services are disabled. Use the " +
                                "Settings charm to enable them.";
                    break;

                case PositionStatus.NotInitialized:
                    strStatus = "Location status is not initialized because " +
                                "the app has not yet requested location data.";
                    break;

                case PositionStatus.NotAvailable:
                    strStatus = "Location services are not supported on your system.";
                    break;

                default:
                    strStatus = "Unknown PositionStatus value (" + 
                                newStatus.ToString() + ").";
                    break;
            }

            _cd.InvokeAsync(CoreDispatcherPriority.Normal, (s, a) =>
            {
               TextBox1.Text += strStatus + "\n";
            }, this, args);

        }

    }
}