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和添加标记的不同方法。
地图活动.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) {}
});
}
我的日志猫：
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)
您正在 ChildEventListener 中添加标记，onChildAdded()仅针对每个现有子项以及将新子项添加到您正在侦听的引用时调用。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，您将看到它确实显示了标记。 如果您尝试获取子引用的值，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());
}
});