Android 位置應用程序在添加 Firebase 后崩潰

Question

我嘗試使用 Android 工作室在 Google map 上創建位置標記，並從 Firebase 實時數據庫獲取位置。 在我將 Firebase 實時數據庫添加到我的應用程序后，它一直在崩潰。 請幫忙。 這是 MapsActivity.JAVA 代碼

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {


String latitude,longitude,value;
int n,n1;
float x,y;
FirebaseDatabase firebaseDatabase;
DatabaseReference databaseReference;

private GoogleMap mMap;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);

    firebaseDatabase = FirebaseDatabase.getInstance();
    databaseReference = firebaseDatabase.getReference("device");

    databaseReference.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            value = dataSnapshot.getValue().toString();

            n = value.indexOf("attitude=0");

            latitude = value.substring(n+10,n+17);
            longitude  =  value.substring(n+28,n1+34);

            x = Float.parseFloat(latitude);
            y = Float.parseFloat(longitude);


        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

       }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);
};

/**
 * Manipulates the map once available.
 * This callback is triggered when the map is ready to be used.
 * This is where we can add markers or lines, add listeners or move the camera. In this case,
 * we just add a marker near Sydney, Australia.
 * If Google Play services is not installed on the device, the user will be prompted to install
 * it inside the SupportMapFragment. This method will only be triggered once the user has
 * installed Google Play services and returned to the app.
 */
@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
   // x = (float) 13.9365;
   // y = (float) 100.4991;

    x = Float.parseFloat(latitude);
     y = Float.parseFloat(longitude);

    // Add a marker in Sydney and move the camera
    LatLng sydney = new LatLng(x, y);
    mMap.addMarker(new MarkerOptions().position(sydney).title("Device1"));
    mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));



}}

這似乎是個問題

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.smart, PID: 13831
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.trim()' on a null object reference
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1838)
    at sun.misc.FloatingDecimal.parseFloat(FloatingDecimal.java:122)
    at java.lang.Float.parseFloat(Float.java:451)
    at com.example.smartbin.MapsActivity.onMapReady(MapsActivity.java:98)
    at com.google.android.gms.maps.zzak.zza(Unknown Source:2)
    at com.google.android.gms.maps.internal.zzaq.dispatchTransaction(Unknown Source:12)
    at com.google.android.gms.internal.maps.zzb.onTransact(Unknown Source:12)
    at android.os.Binder.transact(Binder.java:667)
    at cx.b(:com.google.android.gms.dynamite_mapsdynamite@201817068@20.18.17 (100700-0):2)
    at com.google.maps.api.android.lib6.impl.be.run(:com.google.android.gms.dynamite_mapsdynamite@201817068@20.18.17 (100700-0):2)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

路徑是唯一鍵我不知道如何創建路徑，所以我嘗試 substring 並將其變成浮點數。 謝謝

Answer 1

似乎x = Float.parseFloat(latitude)崩潰了，因為緯度是 null。 你在這條線上初始化緯度的值latitude = value.substring(n+10,n+17); , 這只會在有子添加到 FirebaseDatabase 時運行，所以當onMapReady被調用時，沒有子添加到數據庫，所以緯度是 null。