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

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<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：

/** 
  * 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。