Question

我正在尝试在应用中使用位置管理器当我尝试使用位置管理器的对象空指针异常被抛出这里是我的snipet

 public class MainActivity extends Activity {

LocationManager locationManager;
float[] dist;
double rest;
Long res ;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    String serviceString = MainActivity.this.LOCATION_SERVICE;
    locationManager= (LocationManager)getSystemService(serviceString);
    String provider = LocationManager.GPS_PROVIDER;
    final Location loc1=locationManager.getLastKnownLocation(provider);
    String l = Double.toString(loc1.getLatitude());
  //  Log.d("Message: ",l);
    String netprovider=LocationManager.NETWORK_PROVIDER;

    LocationListener my = new LocationListener() {
       // double lat1 = loc1.getLatitude();
        //double  lon1=loc1.getLongitude();

        @Override
        public void onLocationChanged(Location loc1) {
            /*Location.distanceBetween(lat1,lon1,loc1.getLatitude(),loc1.getLongitude(),dist);
                res+=(long)dist[0];*/
                Toast.makeText(MainActivity.this,"Location changed",Toast.LENGTH_LONG).show();
                Log.d("Message: ", "Location changed, " + loc1.getAccuracy() + " , " + loc1.getLatitude() + "," + loc1.getLongitude());

        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {

        }

        @Override
        public void onProviderEnabled(String provider) {

        }

        @Override
        public void onProviderDisabled(String provider) {

        }
    };
    locationManager.requestLocationUpdates(provider, 1000, 1, my);
}

请帮我解决问题。

和logcat

Process: com.example.pragadeeswaran.distancecalculator, PID: 9468
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.pragadeeswaran.distancecalculator/com.example.pragadeeswaran.distancecalculator.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2252)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2301)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
            at android.os.Handler.dispatchMessage(Handler.java:106)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5196)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

getLastKnownLocation()可以返回null，因此您应该检查它：

String l;
if(loc1 != null)
    l = Double.toString(loc1.getLatitude());

Answer 2

尝试替换此行

locationManager= (LocationManager)getSystemService(serviceString);

这一个

locationManager = (LocationManager)this.getSystemService(Context.LOCATION_SERVICE);

调用位置管理器时出现空指针异常

2 个答案: