getLastKnownLocation 返回null

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

 <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" />

 <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

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

 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

   /**
     * 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);
 }

   /**
     * 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. 

转自：http://blog.csdn.net/L_serein/article/details/6127300