Android打开GPS导航并获取位置信息返回null解决方案
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) { Log.i("onLocationChanged", "come in"); if (location != null) { Log.w("Location","Current altitude = "+ location.getAltitude()); Log.w("Location","Current latitude = "+ location.getLatitude()); } }
经过测试,经过一段时间后可以获取Location(获取时间与minTime、minDistance相关)。还需注意的一个问题是在设置了监听器后,删除监听器之前不能用上面的方法关闭gps,否则会报错。因此关闭gps的方法是
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> <uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION"></uses-permission> <uses-permission android:name="android.permission.UPDATE_DEVICE_STATS"></uses-permission>
import android.app.Activity; import android.content.Context; import android.location.Criteria; import android.location.Location; import android.location.LocationListener; import android.location.LocationManager; import android.os.Bundle; import android.util.Log; public class audio extends Activity { /** Called when the activity is first created. */ LocationManager locationManager; LocationListener llistener; String provider; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Criteria criteria = new Criteria(); criteria.setAccuracy(Criteria.ACCURACY_FINE); criteria.setAltitudeRequired(false); criteria.setBearingRequired(false); criteria.setCostAllowed(true); criteria.setPowerRequirement(Criteria.POWER_LOW); String serviceName = Context.LOCATION_SERVICE; locationManager = (LocationManager) getSystemService(serviceName); locationManager.setTestProviderEnabled("gps", true); provider = locationManager.getBestProvider(criteria, true); Log.d("provider", provider); llistener = new LocationListener() { @Override public void onLocationChanged(Location location) { // TODO Auto-generated method stub Log.i("onLocationChanged", "come in"); if (location != null) { Log.w("Location", "Current altitude = " + location.getAltitude()); Log.w("Location", "Current latitude = " + location.getLatitude()); } locationManager.removeUpdates(this); locationManager.setTestProviderEnabled(provider, false); } @Override public void onProviderDisabled(String provider) { // TODO Auto-generated method stub Log.i("onProviderDisabled", "come in"); } @Override public void onProviderEnabled(String provider) { // TODO Auto-generated method stub Log.i("onProviderEnabled", "come in"); } @Override public void onStatusChanged(String provider, int status, Bundle extras) { // TODO Auto-generated method stub Log.i("onStatusChanged", "come in"); } }; locationManager.requestLocationUpdates(provider, 1000, (float) 1000.0, llistener); } protected void onDestroy() { locationManager.removeUpdates(llistener); locationManager.setTestProviderEnabled(provider, false); super.onDestroy(); }
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