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我從Firebase數據庫讀取一些數據，並返回對象爲null。FireBase數據庫空對象
我嘗試了很多方法。當我有（如現在在代碼中）
marker(mMap.addMarker(new MarkerOptions().position(new LatLng(value, value2)).title("Mehehe"));)
onDataChange之外的方法發生錯誤。但是當我把標誌物onDataChange方法和設置都：
DatabaseReference myRef2 = database2.getReference("latitude");
和
DatabaseReference myRef = database.getReference("latitude");
如果有類似getRefrences沒有錯誤，但如果我嘗試
DatabaseReference myRef2 = database2.getReference("latitude");
和
DatabaseReference myRef = database.getReference("longitude");
然後出現類似的錯誤，例如.addMarker在onDataChange方法之外。
public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, LocationListener, View.OnClickListener {
private ImageView imageView;
private GoogleMap mMap;
private GoogleApiClient client;
private DatabaseReference mDatabase;
private String email;
private double latitude;
private double longitude;
Double value;
Double value2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
// 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);
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("[email protected] - username");
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// This method is called once with the initial value and again
// whenever data at this location is updated.
String value = dataSnapshot.getValue(String.class);
Log.d("TAG", "Value is: " + value);
Toast.makeText(getApplicationContext(), value.toString(), Toast.LENGTH_SHORT).show();
}
@Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w("TAG", "Failed to read value.", error.toException());
Toast.makeText(getApplicationContext(), error.toException().toString(), Toast.LENGTH_SHORT).show();
}
});
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
imageView = (ImageView) findViewById(R.id.imageView);
imageView.setOnClickListener(this);
}
@Override
public void onClick(View view) {
if (view == imageView) {
Intent intent = new Intent(getApplicationContext(), ProfileSetUp.class);
startActivity(intent);
}
}
/**
* 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;
if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
mMap.setMyLocationEnabled(true);
LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
String provider = locationManager.getBestProvider(criteria, true);
Location myLocation = locationManager.getLastKnownLocation(LocationManager.PASSIVE_PROVIDER);
// Location myLocation = locationManager.getLastKnownLocation(provider);
mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
// double latitude = myLocation.getLatitude();
// double longitude = myLocation.getLongitude();
latitude = myLocation.getLatitude();
longitude = myLocation.getLongitude();
mDatabase = FirebaseDatabase.getInstance().getReference();
// mDatabase.child("latitude").setValue(latitude);
// mDatabase.child("longitude").setValue(longitude);
LatLng latLng = new LatLng(latitude, longitude);
mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
mMap.animateCamera(CameraUpdateFactory.zoomTo(14));
mMap.addMarker(new MarkerOptions().position(new LatLng(latitude, longitude)).title("You are here!").snippet("Consider yourself located"));
// mMap.addMarker(new MarkerOptions().position(new LatLng(48.7352022, 19.1187914)).title("You are here!").snippet("Consider yourself located"));
FirebaseDatabase database2 = FirebaseDatabase.getInstance();
DatabaseReference myRef2 = database2.getReference("latitude");
myRef2.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// This method is called once with the initial value and again
// whenever data at this location is updated.
value2 = dataSnapshot.getValue(Double.class);
Log.d("TAG", "Value is: " + value2);
// Toast.makeText(getApplicationContext(), value3.toString(), Toast.LENGTH_SHORT).show();
Toast.makeText(getApplicationContext(), value2.toString(), Toast.LENGTH_SHORT).show();
}
@Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w("TAG", "Failed to read value.", error.toException());
// Toast.makeText(getApplicationContext(), error.toException().toString(), Toast.LENGTH_SHORT).show();
}
});
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("longitude");
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// This method is called once with the initial value and again
// whenever data at this location is updated.
value = dataSnapshot.getValue(Double.class);
Log.d("TAG", "Value is: " + value);
// mMap.addMarker(new MarkerOptions().position(new LatLng(value, value2)).title("Mehehe"));
Toast.makeText(getApplicationContext(), value.toString(), Toast.LENGTH_SHORT).show();
Toast.makeText(getApplicationContext(), value2.toString(), Toast.LENGTH_SHORT).show();
}
@Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w("TAG", "Failed to read value.", error.toException());
// Toast.makeText(getApplicationContext(), error.toException().toString(), Toast.LENGTH_SHORT).show();
}
});
mMap.addMarker(new MarkerOptions().position(new LatLng(value, value2)).title("Mehehe"));
}
@Override
public void onLocationChanged(Location location) {
}
}
而且有錯誤信息： -
08-15 10:47:53.591 4280-4280/com.samo.facedatefb E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.samo.facedatefb, PID: 4280
java.lang.NullPointerException: Attempt to invoke virtual method 'double java.lang.Double.doubleValue()' on a null object reference
at com.samo.facedatefb.MapsActivity.onMapReady(MapsActivity.java:268)
at com.google.android.gms.maps.SupportMapFragment$zza$1.zza(Unknown Source)
at com.google.android.gms.maps.internal.zzt$zza.onTransact(Unknown Source)
at android.os.Binder.transact(Binder.java:385)
at xz.a(:com.google.android.gms.DynamiteModulesB:82)
at maps.ad.u$5.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5549)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:964)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:759)
我的火力數據庫片段。
爲什麼使用完全相同的FirebaseDatabase對象的多個實例？ –
當您調用'mMap.addMarker（new MarkerOptions（）。position（new LatLng（value，value2））。title（「Mehehe」））;''value'和'value2'設置爲'null' ？ – Poger