最近在做一個(gè) Android 項目，需要用到GPS獲取位置信息，從 API 查了一下，發(fā)現獲取位置信息僅需極其簡(jiǎn)單的一句即可：
getLastKnownLocation(LocationManager.GPS_PROVIDER),
于是高興地不得了?？墒且粚?xiě)進(jìn)代碼里，返回值（Location類(lèi)型）居然一直為null..郁悶的不得了。在網(wǎng)上查了好久，發(fā)現好多人都和我一樣糾結于這個(gè)問(wèn)題上，有人說(shuō)是因為GPS沒(méi)打開(kāi)，也有人說(shuō)是相關(guān)權限沒(méi)加上..可是我的明明已經(jīng)在設置里打開(kāi)，權限自然也加上了。在api上糾結了半天，終于找出原因了，原來(lái)要打開(kāi)GPS其實(shí)在于這句：
setTestProviderEnabled("gps",true);
而跟手機上的設置沒(méi)多大關(guān)系（起碼在我的手機上測是這樣的）。手機上的設置關(guān)閉了，這一句照樣能打開(kāi)；而即使手機設置打開(kāi)了，沒(méi)這一句也是白搭。與這句對應的是
setTestProviderEnabled("gps",false);
用來(lái)關(guān)閉GPS.
GPS打開(kāi)后可以用上面的方法獲取Location了嗎？還是不可以！確切地說(shuō)是有時(shí)候可以，因為這個(gè)函數獲取的是上次已經(jīng)獲得的位置信息，設想如果此程序第一次跑，先前并沒(méi)有獲取過(guò)位置信息，當然返回值為null了。經(jīng)仔細查看api，在
requestLocationUpdates (String provider, long minTime, float minDistance, LocationListener listener)
里發(fā)現了這樣一句話(huà)：It may take a while to receive the most recent location. Ifan immediate location is required, applications may use thegetLastKnownLocation(String) method.因此為了獲取位置信息，應該用此方法為manager設置監聽(tīng)器，在監聽(tīng)器中onLocationChanged(Locationlocation)里獲取。
測試代碼如下：
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());
}
}
經(jīng)過(guò)測試，經(jīng)過(guò)一段時(shí)間后可以獲取Location（獲取時(shí)間與minTime、minDistance相關(guān)）。還需注意的一個(gè)問(wèn)題是在設置了監聽(tīng)器后，刪除監聽(tīng)器之前不能用上面的方法關(guān)閉gps，否則會(huì )報錯。因此關(guān)閉gps的方法是
manager.removeUpdates (listener);//listener 即為監聽(tīng)器實(shí)例
manager.setTestProviderEnabled("gps",false);
以下是測試代碼，所需權限有：
<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>
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 }
