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 

<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 

来源：http://fzlihui.javaeye.com/blog/713050