NullPointerException - Location&LocationManager - double

Question

我从以下代码行得到一个空指针异常:

    double longitude = location.getLongitude();

我有一个问题,弄清楚问题是什么.

    LocationManager locManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
    locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, waypointActivity);

    //LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 
    Location location = locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
    double longitude = location.getLongitude();
    double latitude = location.getLatitude();
    String locLat = String.valueOf(latitude)+","+String.valueOf(longitude);

这是logcat输出:

04-30 10:20:54.988: E/AndroidRuntime(1827): FATAL EXCEPTION: main
04-30 10:20:54.988: E/AndroidRuntime(1827): java.lang.RuntimeException: Unable to instantiate application android.app.Application: java.lang.NullPointerException
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.LoadedApk.makeApplication(LoadedApk.java:504)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4364)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.ActivityThread.access$1300(ActivityThread.java:141)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1294)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.os.Looper.loop(Looper.java:137)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.ActivityThread.main(ActivityThread.java:5041)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at java.lang.reflect.Method.invokeNative(Native Method)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at java.lang.reflect.Method.invoke(Method.java:511)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at dalvik.system.NativeStart.main(Native Method)
04-30 10:20:54.988: E/AndroidRuntime(1827): Caused by: java.lang.NullPointerException
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.LoadedApk.initializeJavaContextClassLoader(LoadedApk.java:379)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.LoadedApk.getClassLoader(LoadedApk.java:322)
04-30 10:20:54.988: E/AndroidRuntime(1827):     at android.app.LoadedApk.makeApplication(LoadedApk.java:496)
04-30 10:20:54.988: E/AndroidRuntime(1827):     ... 11 more
04-30 10:21:04.048: E/Trace(1863): error opening trace file: No such file or directory (2)

我无法理解为什么它认为我的位置变量为空.任何建议,将不胜感激.

Answer 1

该文件规定:

返回一个位置,指示从给定提供程序获取的上次已知位置修复的数据.

这可以在不启动提供程序的情况下完成.请注意,此位置可能已过期,例如,如果设备已关闭并移至其他位置.

如果当前禁用了提供程序,则返回null.

由于GPS位置为空,您可能没有打开GPS或手机没有GPS.

将您的代码更改为

Location location = locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location!=null){
   double longitude = location.getLongitude();
   double latitude = location.getLatitude();
   String locLat = String.valueOf(latitude)+","+String.valueOf(longitude);
}