android定位的实现

基于android的定位无非就两种：network、gps。两者各有优劣。
Network:定位快，准确度低，受环境影响小。
GPS：定位慢，准确度高，受环境影响大。

本文要解决的问题：
1.      locationManager.getLastKnownLocation方法返回null。
2.      如何实现快速而又精确的定位。

E文好的话，直接看官网就好了http://developer.android.com/guide/topics/location/strategies.html

在你的程序里如果有这样的代码你就要注意了(现在看来这些倒是多余了)

Criteria criteria = new Criteria();
        criteria.setAccuracy(Criteria.ACCURACY_FINE);//高精度
        criteria.setAltitudeRequired(false);//无海拔要求
        criteria.setBearingRequired(false);//无方位要求
        criteria.setCostAllowed(true);//允许产生资费
        criteria.setPowerRequirement(Criteria.POWER_LOW);//低功耗
      
        // 获取最佳服务对象
        String provider = locationManager.getBestProvider(criteria,true);
locationManager.getLastKnownLocation(provider);

locationManager.getBestProvider(criteria,true);方法看起来很完美，但其实返回值就network、gps二选一。而且如果你要求高精度，它会优先检查GPS，如果手机开启了GPS就返回GPS，否则返回network。如果都没开启则返回null。
结合Network、GPS两种定位方式的优劣不难看出为什么getLastKnownLocation方法会返回null（这只针对第一次定位）。

当你开启GPS，provider的值为GPS。这时的定位方式为GPS，由于GPS定位慢(我测试的时间大约为50秒)，所以它不可能立即返回你一个Location对象，所以就返回null了。还有人用下面的方法解决这个问题：

    while (location ==null) {
           location = locationManager.getLastKnownLocation(provider);
       }

这绝对是个愚蠢的做法！举个例子：如果你在室内，gps无法定位到，你的程序将陷入死循环。当然使用requestLocationUpdates可以做到定位且不让程序陷入死循环，但是定位耗时长，甚至得不到定位。
如果使用网络定位呢，不得说这也是一个不错的选择。locationManager.requestLocationUpdates(
              LocationManager.NETWORK_PROVIDER, 0, 0,networkListener);
网络定位耗时一般在2秒左右（网络差，时间会更长），只要你接入网络，基本上都能获得定位。唯一的缺点就是精度不高。

那能不能将两者结合，这也是本文的重点。既然结合两者，就要同时为两者添加监听

locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,1000 * 2,50,gpsListener);
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0,networkListener);

这样，大概2秒我们就可以得到来自网络的定位，一分钟后得到来自GPS定位。这时用GPS定位替换网络定位就好了。当然这只是个理想的情况，现实要复杂的多。
比如：
你第一次定位成功返回location，由于网络问题第二次返回null。这时会发现，更新的location没有上次的精确，甚至是null，无法使用，这时我们要判断当前的location和新获得的location那个更好。可能你获得GPS定位后，由于天气、进入隧道等原因GPS服务器丢失，无法更新location（这时一个好的做法是切换到network定位）。还有可能用户没有开启GPS和network，根本就谈不上定位（其实每次定位成功都会有个定位缓存的，可以使用getLastKnownLocation获得）。

终上所述，我们要做的就是：
1.  尝试通过getLastKnownLocation获取上次定位信息
2.  开启network和gps监听
3.  获得network定位信息location
4.  比较当前location和新获取的location哪个更好（来自network）
5.  获得gps定位信息location
6.  停掉network监听
7.  比较当前location和新获取的location哪个更好（来自gps）
8.  如果gps服务器丢失，重新开启network监听

以GPS监听为例

   // GPS监听的回调函数
    private class GPSLocationListener implements LocationListener {
 
       private boolean isRemove = false;//判断网络监听是否移除
 
       @Override
       public void onLocationChanged(Location location) {
           // TODO Auto-generatedmethod stub
           boolean flag =betterLocation.isBetterLocation(location,
                  currentBestLocation);
 
           if (flag) {
              currentBestLocation = location;
              updateLocation(currentBestLocation);
           }
           // 获得GPS服务后，移除network监听
           if (location !=null && !isRemove) {
              locationManager.removeUpdates(networkListener);
              isRemove = true;
           }
       }
 
       @Override
       public void onProviderDisabled(String provider) {
           // TODO Auto-generatedmethod stub
       }
 
       @Override
       public void onProviderEnabled(String provider) {
           // TODO Auto-generatedmethod stub
       }
 
       @Override
       public void onStatusChanged(String provider, int status, Bundleextras) {
           // TODO Auto-generatedmethod stub
           if (LocationProvider.OUT_OF_SERVICE == status) {
              Toast.makeText(MainActivity.this,"GPS服务丢失,切换至网络定位",
                     Toast.LENGTH_SHORT).show();
              locationManager
                     .requestLocationUpdates(
                            LocationManager.NETWORK_PROVIDER, 0, 0,
                            networkListener);
           }
       }
    }

其中isBetterLocation是用来判断哪个location更好的。这个方法来自android官网的，通过location获取的时间，精度等信息进行判断。

private static final int TWO_MINUTES = 1000 * 60 * 2;
/** 
     * Determines whether one Location reading is better than the current 
     * Location fix 
     *  
     * @param location 
     *            The new Location that you want to evaluate 
     * @param currentBestLocation 
     *            The current Location fix, to which you want to compare the new 
     *            one 
     */  
    protected boolean isBetterLocation(Location location,  
            Location currentBestLocation) {  
        if (currentBestLocation == null) {  
            // A new location is always better than no location  
            return true;  
        }  
  
        // Check whether the new location fix is newer or older  
        long timeDelta = location.getTime() - currentBestLocation.getTime();  
        boolean isSignificantlyNewer = timeDelta > TWO_MINUTES;  
        boolean isSignificantlyOlder = timeDelta < -TWO_MINUTES;  
        boolean isNewer = timeDelta > 0;  
  
        // If it's been more than two minutes since the current location, use  
        // the new location  
        // because the user has likely moved  
        if (isSignificantlyNewer) {  
            return true;  
            // If the new location is more than two minutes older, it must be  
            // worse  
        } else if (isSignificantlyOlder) {  
            return false;  
        }  
  
        // Check whether the new location fix is more or less accurate  
        int accuracyDelta = (int) (location.getAccuracy() - currentBestLocation  
                .getAccuracy());  
        boolean isLessAccurate = accuracyDelta > 0;  
        boolean isMoreAccurate = accuracyDelta < 0;  
        boolean isSignificantlyLessAccurate = accuracyDelta > 200;  
  
        // Check if the old and new location are from the same provider  
        boolean isFromSameProvider = isSameProvider(location.getProvider(),  
                currentBestLocation.getProvider());  
  
        // Determine location quality using a combination of timeliness and  
        // accuracy  
        if (isMoreAccurate) {  
            return true;  
        } else if (isNewer && !isLessAccurate) {  
            return true;  
        } else if (isNewer && !isSignificantlyLessAccurate  
                && isFromSameProvider) {  
            return true;  
        }  
        return false;  
    }  
  
    /** Checks whether two providers are the same */  
    private boolean isSameProvider(String provider1, String provider2) {  
        if (provider1 == null) {  
            return provider2 == null;  
        }  
        return provider1.equals(provider2);  
    }  

因为之前上传的demo，大家觉得意义不大，所以就不再提供了。
下图的‘微秒’单位错了，应该是毫秒




andriod 自动切换网络和gps定位
获取到位置服务以后，同时请求网络和gps定位更新，然后就会同时上报网络和gps的Location 信息。在没有gps信号的时候，会自动获取网络定位的位置信息，如果有gps信号，则优先获取gps提供的位置信息.isBetterLocation 根据 时间、准确性、定位方式等判断是否更新当前位置信息，该方法来源于开发指南的Obtaining User Location 下。

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;

import android.content.Context;
import android.location.Address;
import android.location.Geocoder;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import cn.tangdada.tangbang.R;

public class SecondFragment extends BaseFragment
{

    private TextView tv;

    LocationManager lm = null;

    Location myLocation = null;

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd  HH:mm:ss.SSSZ");

    public SecondFragment()
    {
        super();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        super.onCreateView(inflater, container, savedInstanceState);
        View view = inflater.inflate(R.layout.fragment_second, null);
        tv = (TextView) view.findViewById(R.id.tv);

        lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);

        return view;
    }

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
    }

    @Override
    public void onDestroy()
    {
        // TODO Auto-generated method stub
        super.onDestroy();
    }

    @Override
    public void onPause()
    {
        // TODO Auto-generated method stub
        super.onPause();
        lm.removeUpdates(listener);
    }

    @Override
    public void onResume()
    {
        // TODO Auto-generated method stub
        super.onResume();
        lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, listener);
        lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, listener);
    }

    LocationListener listener = new LocationListener()
    {

        @Override
        public void onLocationChanged(Location location)
        {
            // 实际上报时间
            // String time = sdf.format(new Date(location.getTime()));
            // timeText.setText("实际上报时间：" + time);

            if (isBetterLocation(location, myLocation))
            {
                // 获取纬度
                double lat = location.getLatitude();
                // 获取经度
                double lon = location.getLongitude();
                // 位置提供者
                String provider = location.getProvider();
                // 位置的准确性
                float accuracy = location.getAccuracy();
                // 高度信息
                double altitude = location.getAltitude();
                // 方向角
                float bearing = location.getBearing();
                // 速度 米/秒
                float speed = location.getSpeed();

                String locationTime = sdf.format(new Date(location.getTime()));
                String currentTime = null;

                if (myLocation != null)
                {
                    currentTime = sdf.format(new Date(myLocation.getTime()));
                    myLocation = location;

                }
                else
                {
                    myLocation = location;
                }

                // 获取当前详细地址
                StringBuffer sb = new StringBuffer();
                if (myLocation != null)
                {
                    Geocoder gc = new Geocoder(context);
                    List<Address> addresses = null;
                    try
                    {
                        addresses = gc.getFromLocation(myLocation.getLatitude(), myLocation.getLongitude(), 1);
                    }
                    catch (IOException e)
                    {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }

                    if (addresses != null && addresses.size() > 0)
                    {
                        Address address = addresses.get(0);
                        sb.append(address.getCountryName() + address.getLocality());
                        sb.append(address.getSubThoroughfare());

                    }
                }

                tv.setText("经度：" + lon + "\n纬度：" + lat + "\n服务商：" + provider + "\n准确性：" + accuracy + "\n高度：" + altitude + "\n方向角：" + bearing
                        + "\n速度：" + speed + "\n上次上报时间：" + currentTime + "\n最新上报时间：" + locationTime + "\n您所在的城市：" + sb.toString());

            }

        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras)
        {
            Log.i("tag", "onStatusChanged: " + provider);

        }

        @Override
        public void onProviderEnabled(String provider)
        {
            Log.i("tag", "onProviderEnabled: " + provider);
        }

        @Override
        public void onProviderDisabled(String provider)
        {
            Log.i("tag", "onProviderDisabled: " + provider);
        }

    };

    private static final int TWO_MINUTES = 1000 * 1 * 2;

    /**
     * Determines whether one Location reading is better than the current Location fix
     * 
     * @param location The new Location that you want to evaluate
     * @param currentBestLocation The current Location fix, to which you want to compare the new one
     */
    protected boolean isBetterLocation(Location location, Location currentBestLocation)
    {
        if (currentBestLocation == null)
        {
            // A new location is always better than no location
            return true;
        }

        // Check whether the new location fix is newer or older
        long timeDelta = location.getTime() - currentBestLocation.getTime();
        boolean isSignificantlyNewer = timeDelta > TWO_MINUTES;
        boolean isSignificantlyOlder = timeDelta < -TWO_MINUTES;
        boolean isNewer = timeDelta > 0;

        // If it's been more than two minutes since the current location, use
        // the new location
        // because the user has likely moved
        if (isSignificantlyNewer)
        {
            return true;
            // If the new location is more than two minutes older, it must be
            // worse
        }
        else if (isSignificantlyOlder)
        {
            return false;
        }

        // Check whether the new location fix is more or less accurate
        int accuracyDelta = (int) (location.getAccuracy() - currentBestLocation.getAccuracy());
        boolean isLessAccurate = accuracyDelta > 0;
        boolean isMoreAccurate = accuracyDelta < 0;
        boolean isSignificantlyLessAccurate = accuracyDelta > 200;

        // Check if the old and new location are from the same provider
        boolean isFromSameProvider = isSameProvider(location.getProvider(), currentBestLocation.getProvider());

        // Determine location quality using a combination of timeliness and
        // accuracy
        if (isMoreAccurate)
        {
            return true;
        }
        else if (isNewer && !isLessAccurate)
        {
            return true;
        }
        else if (isNewer && !isSignificantlyLessAccurate && isFromSameProvider)
        {
            return true;
        }
        return false;
    }

    /** Checks whether two providers are the same */
    private boolean isSameProvider(String provider1, String provider2)
    {
        if (provider1 == null)
        {
            return provider2 == null;
        }
        return provider1.equals(provider2);
    }

}