Android GPS getLastKnownLocation()返回null的解决

在使用LocationManager.getLastKnownLocation("gps")获取gps定位的过程中老是报空指针异常

在网上百度查了不少资料发现这个问题多出现在2.0以上版本
解决方法多是:
1.在AndroidManifest.xml中添加
Xml代码

1. <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
2. <uses-permission android:name="android.permission.INTERNET" />
3. <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

2.在emulator control中手动设置经纬度

但是我的程序这些都写了依旧报空指针

后来在外国论坛上终于找到一些启发
一个哥们这样写代码
Java代码

1. LocationManager mgr = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
2. Location location = mgr.getLastKnownLocation(bundle.getString("provider"));
3. while(location == null)
4. {
5. mgr.requestLocationUpdates("gps", 60000, 1, locationListener);
6. }

LocationManager mgr = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Location location = mgr.getLastKnownLocation(bundle.getString("provider"));
while(location  == null)
{
  mgr.requestLocationUpdates("gps", 60000, 1, locationListener);
}

我试了一下还真有效,他的解释是用debug发现getLastKnownLocation()方法不是一次就能定位的，必须多次才能成功。

但是显然这样用循环一直等待很没效率,所以我重写了MapActivity的方法
Java代码

1. /**
2. * 这里一定要对LocationManager进行重新设置监听
3. * mgr获取provider的过程不是一次就能成功的
4. * mgr.getLastKnownLocation很可能返回null
5. * 如果只在initProvider()中注册一次监听则基本很难成功
6. */
7. @Override
8. protected void onResume() {
9. super.onResume();
10. mgr.requestLocationUpdates(bundle.getString("provider"), 60000, 1, locationListener);
11. }
13. @Override
14. protected void onPause() {
15. super.onPause();
16. mgr.removeUpdates(locationListener);
17. }

   /**
     * 这里一定要对LocationManager进行重新设置监听
     * mgr获取provider的过程不是一次就能成功的
     * mgr.getLastKnownLocation很可能返回null
     * 如果只在initProvider()中注册一次监听则基本很难成功
     */
	@Override
	protected void onResume() {
		super.onResume();
		mgr.requestLocationUpdates(bundle.getString("provider"), 60000, 1, locationListener);
	}

	@Override
	protected void onPause() {
		super.onPause();
		mgr.removeUpdates(locationListener);
	}

一样也成功了。。

在外国技术论坛上找了个解释，个人感觉很贴切:

The call to request update for a location is not blocking, hence it wont wait there. Also the provider in emulator may not have been started.

A possible check could be to see if the settings in it disable gps provider ? then send geo fix.

However, I would use Location Listener, it would be ideal in your case since you need a geo fix to proceed further.Location Listener is Used for receiving notifications from the LocationManager when the location has changed. You can unregister the listener after first geofix.

Note: It can take some time on device to get current location, and even on device this can return null.


具体可见 http://stackoverflow.com/questions/1608632/android-locationmanager-getlastknownlocation-returns-null