getLastKnownLocation()回到null的解决

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     */@Overrideprotected void onResume() {super.onResume();mgr.requestLocationUpdates(bundle.getString("provider"), 60000, 1, locationListener);}@Overrideprotected 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

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