Question

我正在使这个类获取用户的当前位置并将其与数据库中的经度和纬度进行比较，它给出了空指针异常，有人可以帮助我吗？我只想与纬度进行比较，我希望得到50范围内的所有物体。

public class locationFinder extends ListActivity implements LocationListener {

    EgyptDataSource datasource;
    Location locObject;
    String loc;
    double lat;
    double longi;
    List<Integer> indexes;
    List<Hotel> newHotels = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

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

        Intent i = getIntent();
        String category = i.getStringExtra("category");

        if(category.equals("hotels"))
        {
            List<Hotel> Latvalues = datasource.getAllHotelsLat();

            float[] distance = new float[Latvalues.size()];
            for (int j = 0; j < Latvalues.size(); j++) {
            Location.distanceBetween(lat, longi, Latvalues.get(j).toDoubleLat(), 0.0, distance);
            if(distance[0] <50)
            {
                indexes.add(j);
            }
        }
        List<Hotel> allHotels = datasource.getAllHotels();
        for (int q = 0; q < allHotels.size(); q++) {
            for (int w = 0; w < indexes.size(); w++) {
                if(q == indexes.get(w))
                {
                    newHotels.add(allHotels.get(q));
                }
            }
        }

        if (newHotels.isEmpty())
        {
            Toast.makeText(this, "No results found!", Toast.LENGTH_LONG).show();
            Intent i1 = new Intent(locationFinder.this, hotelSearch.class);
            startActivity(i1);
        }

        ArrayAdapter<Hotel> adapter = new ArrayAdapter<Hotel>(this, android.R.layout.simple_list_item_1, newHotels);
        setListAdapter(adapter);

        }
    }

    public void onLocationChanged(Location location) {
        lat = location.getLatitude();
        longi = location.getLongitude();        
    }

    public void onProviderDisabled(String provider) {       
}

public void onProviderEnabled(String provider) {        
}

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

}

这是LogCat

06-22 18:29:04.261: E/AndroidRuntime(30183): FATAL EXCEPTION: main
06-22 18:29:04.261: E/AndroidRuntime(30183): java.lang.RuntimeException: Unable to start activity ComponentInfo{egypt.interfaceAct/egypt.interfaceAct.locationFinder}: java.lang.NullPointerException
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2781)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2797)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.app.ActivityThread.access$2300(ActivityThread.java:135)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2132)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.os.Handler.dispatchMessage(Handler.java:99)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.os.Looper.loop(Looper.java:143)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.app.ActivityThread.main(ActivityThread.java:4914)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at java.lang.reflect.Method.invokeNative(Native Method)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at java.lang.reflect.Method.invoke(Method.java:521)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at dalvik.system.NativeStart.main(Native Method)
06-22 18:29:04.261: E/AndroidRuntime(30183): Caused by: java.lang.NullPointerException
06-22 18:29:04.261: E/AndroidRuntime(30183):    at egypt.interfaceAct.locationFinder.onCreate(locationFinder.java:47)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1065)
06-22 18:29:04.261: E/AndroidRuntime(30183):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2745)
06-22 18:29:04.261: E/AndroidRuntime(30183):    ... 11 more

Answer 1

您尚未初始化newHotels变量。在onCreate方法的开头添加以下行：

newHotels = new ArrayList<Hotel>();

Answer 2

在使用之前，您可能还需要检查类别：

String category = i.getStringExtra("category");

if(category.equals("hotels"))

注意类别可能为null，因此您最好执行以下操作：

if(category != null && category.equals("hotels"))

Answer 3

您可以通过查找包含您已知＆＃34;知道的类的行来在LogCat中找到您的错误。例如，在你的LogCat中有一行＆＃34;在egypt.interfaceAct.locationFinder.onCreate（locationFinder.java:47）＆＃34;

来自LogCat中的所有类，这是最知名的类，因此您可以在第47行检查类locationFinder并找到第47行的错误。

我假设你的List newHotels仍为null。所以只需用

初始化newsHotels

newHotels = new ArrayList<Hotel>();

在onCreate中添加此代码

经度和纬度NullPointerException

3 个答案: