即使在代码中手动设置位置后，标记也不会显示在地图上

Question

我正在尝试从 Firebase 数据库中检索双精度值（经度和纬度）并将其显示在地图上。问题是标记没有显示在地图上，我认为这是一个数据库错误，但即使我在代码本身中添加纬度和经度，标记也没有显示（如下所示）。请帮助我，谢谢！

我尝试了从数据库中检索数据的不同方法以及添加标记的不同方法。

MapsActivity.java

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.FragmentActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;


public class MapsActivity extends FragmentActivity implements OnMapReadyCallback{

    private GoogleMap mMap;
    private FirebaseAuth mAuth;
    //String value_latitude = "0";
   // String value_longitue = "0";
    double longi = 0;
    double lati = 0;
   // String message = "BUS1";
    Button Refreshh;
    Double latitude = 0.0;
    Double longitdue = 0.0;
    String vali = "BUS1";
    String message = "BUS1";
    Button Backkk;

    private FirebaseDatabase mDatabase = FirebaseDatabase.getInstance();
    private DatabaseReference mDatabaseReference = mDatabase.getReference();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        //Intent intent = getIntent();
        message = getIntent().getExtras().getString("arg");
        vali = message;

        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        //vali = message;

        //Log.d("vali", vali);


    }



    /**
     *
     * 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;
        mMap.clear();


        mDatabaseReference.child("Locations").child(vali).addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, String prevChildKey) {
                LatLng newLocation = new LatLng(
                        dataSnapshot.child("latitude").getValue(Long.class),
                        dataSnapshot.child("longitude").getValue(Long.class)
                );
                  LatLng sydney = new LatLng(13.0640934, 80.2501135);
                mMap.addMarker(new MarkerOptions().position(sydney)
                        .title("Marker in Sydney"));
              mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, String prevChildKey) {}

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {}

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, String prevChildKey) {}

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {}
        });
    }

我的 Logcat：

2019-08-15 23:03:09.134 4869-5490/? E/...lback.CallbackFuture: Timed out waiting for result!
2019-08-15 23:03:09.135 4869-5490/? E/AmazonKindle.com.amazon.kindle.services.authentication.MAPTokenCache: [WebRequestManager-webserviceRequest2-thread-1]: Retrieving of token: com.amazon.dcp.sso.token.cookie.xmainAndXabcCookies failed
    java.util.concurrent.TimeoutException: Timed out waiting for result!
        at com.amazon.identity.auth.device.callback.CallbackFuture.get(CallbackFuture.java:170)
        at com.amazon.identity.auth.device.callback.CallbackFuture.get(CallbackFuture.java:26)
        at com.amazon.kindle.services.authentication.MAPTokenCache.retrieveToken(MAPTokenCache.java:378)
        at com.amazon.kindle.services.authentication.MAPTokenCache.fetchTokenManagementToken(MAPTokenCache.java:338)
        at com.amazon.kindle.services.authentication.MAPTokenCache.fetchValue(MAPTokenCache.java:263)
        at com.amazon.kindle.services.authentication.MAPTokenCache.getValue(MAPTokenCache.java:156)
        at com.amazon.kindle.services.authentication.AccountHoldersKt.getToken(AccountHolders.kt:119)
        at com.amazon.kindle.services.authentication.KindleAuthenticationManager.getToken(KindleAuthenticationManager.kt:185)
        at com.amazon.kindle.krx.application.DeviceInformation.getXmainXacbCookieForDevicePfm(DeviceInformation.java:137)
        at com.amazon.kcp.library.customerbenefits.CustomerBenefitsWebRequest.getHeaders(CustomerBenefitsWebRequest.java:102)
        at com.amazon.kindle.webservices.BaseWebRequestExecutor.connect(BaseWebRequestExecutor.java:536)
        at com.amazon.kindle.webservices.BaseWebRequestExecutor.openConnection(BaseWebRequestExecutor.java:200)
        at com.amazon.kindle.webservices.BaseWebRequestExecutor.execute(BaseWebRequestExecutor.java:121)
        at com.amazon.kindle.webservices.WebRequestManager$WebRequestTask.executeRequest(WebRequestManager.java:125)
        at com.amazon.kindle.webservices.WebRequestManager$WebRequestTask.run(WebRequestManager.java:98)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:764)

Answer 1

您在 ChildEventListener 中添加标记，onChildAdded() 仅在每个现有子项以及新子项添加到您正在收听的引用中时调用。 因此，如果您的引用没有任何子项，则不会调用它。

检查您的 FirebaseReference，您可能访问了错误的孩子。 或者您可能使用了错误的侦听器，如果您将代码移出侦听器，您会看到它确实显示了标记。 如果要获取子引用的值，则必须添加 ValueEventListener：

ref.addValueEventListener(new ValueEventListener() {
  @Override
  public void onDataChange(DataSnapshot dataSnapshot) {
    Post post = dataSnapshot.getValue(Post.class);
    System.out.println(post);
  }

  @Override
  public void onCancelled(DatabaseError databaseError) {
    System.out.println("The read failed: " + databaseError.getCode());
  }
});