最近在做一个 Android 项目,需要用到GPS获取位置信息,从 API 查了一下,发现获取位置信息仅需极其简单的一句即可: getLastKnownLocation(LocationManager.GPS_PROVIDER), 于是高兴地不得了。可是一写进代码里,返回值(Location 类型)居然一直为null..郁闷的不得了。在网上查了好久,发现好多人都和我一样纠结于这个问题上,有人说是因为GPS没打开,也有人说是相关权限没加 上..可是我的明明已经在设置里打开,权限自然也加上了。在api上纠结了半天,终于找出原因了,原来要打开GPS其实在于这句: setTestProviderEnabled("gps",true); 而跟手机上的设置没多大关系(起码在我的手机上测是这样的)。手机上的设置关闭了,这一句照样能打开;而即使手机设置打开了,没这一句也是白搭。与这句对应的是 setTestProviderEnabled("gps",false); 用来关闭GPS. GPS打开后可以用上面的方法获取Location了吗?还是不可以!确切地说是有时候可以,因为这个函数获取的是上次已经获得的位置信息,设想如果此程序第一次跑,先前并没有获取过位置信息,当然返回值为null了。经仔细查看api,在 requestLocationUpdates (String provider, long minTime, float minDistance, LocationListener listener) 里发现了这样一句话:It may take a while to receive the most recent location. If an immediate location is required, applications may use the getLastKnownLocation(String) method. 因此为了获取位置信息,应该用此方法为manager设置监听器,在监听器中onLocationChanged(Location location)里获取。 测试代码如下: public void onLocationChanged(Location location) manager.removeUpdates (listener);//listener 即为监听器实例 manager.setTestProviderEnabled("gps",false);
以下是测试代码,所需权限有: <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"></uses-permission> 1 import android.app.Activity;
2 import android.content.Context; 3 import android.location.Criteria; 4 import android.location.Location; 5 import android.location.LocationListener; 6 import android.location.LocationManager; 7 import android.os.Bundle; 8 import android.util.Log; 9 10 public class audio extends Activity 11 { 12 13 /** Called when the activity is first created. */ 14 LocationManager locationManager; 15 LocationListener llistener; 16 String provider; 17 18 public void onCreate(Bundle savedInstanceState) 19 { 20 super.onCreate(savedInstanceState); 21 setContentView(R.layout.main); 22 23 Criteria criteria = new Criteria(); 24 criteria.setAccuracy(Criteria.ACCURACY_FINE); 25 criteria.setAltitudeRequired(false); 26 criteria.setBearingRequired(false); 27 criteria.setCostAllowed(true); 28 criteria.setPowerRequirement(Criteria.POWER_LOW); 29 String serviceName = Context.LOCATION_SERVICE; 30 locationManager = (LocationManager) getSystemService(serviceName); 31 locationManager.setTestProviderEnabled("gps", true); 32 provider = locationManager.getBestProvider(criteria, true); 33 Log.d("provider", provider); 34 35 llistener = new LocationListener() { 36 @Override 37 public void onLocationChanged(Location location) 38 { 39 // TODO Auto-generated method stub 40 Log.i("onLocationChanged", "come in"); 41 if (location != null) 42 { 43 Log.w("Location", "Current altitude = " 44 + location.getAltitude()); 45 Log.w("Location", "Current latitude = " 46 + location.getLatitude()); 47 } 48 locationManager.removeUpdates(this); 49 locationManager.setTestProviderEnabled(provider, false); 50 } 51 52 @Override 53 public void onProviderDisabled(String provider) 54 { 55 // TODO Auto-generated method stub 56 Log.i("onProviderDisabled", "come in"); 57 58 } 59 60 @Override 61 public void onProviderEnabled(String provider) 62 { 63 // TODO Auto-generated method stub 64 Log.i("onProviderEnabled", "come in"); 65 } 66 67 @Override 68 public void onStatusChanged(String provider, int status, 69 Bundle extras) 70 { 71 // TODO Auto-generated method stub 72 Log.i("onStatusChanged", "come in"); 73 74 } 75 76 }; 77 locationManager.requestLocationUpdates(provider, 1000, (float) 1000.0, llistener); 78 } 79 80 protected void onDestroy() 81 { 82 locationManager.removeUpdates(llistener); 83 locationManager.setTestProviderEnabled(provider, false); 84 super.onDestroy(); 85 }
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来自: techres > 《Android应用》