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" />   

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);       
}     

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

@Override     
protected void onResume() {      
    super.onResume();      
    mgr.requestLocationUpdates(bundle.getString("provider"), 60000, 1, locationListener);      
}      
     
@Override     
protected void onPause() {      
    super.onPause();      
    mgr.removeUpdates(locationListener);      
}     

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.