如何显示 firebase 数据库中的所有标记？

Question

how do I display all markers from the firebase database?

I have come into the database the data in this form:

but only what is highlighted in the drawing is displayed: I write the code like this:

@Override
public void onMapReady(GoogleMap googleMap) {
    if (!isOnline() && !isNetworkAvailable()) {
    } else {
        Map1 = googleMap;
        Map1.setMapType(GoogleMap.MAP_TYPE_NORMAL);

        Map1.setMapStyle(mapStyleOptions);
        Map1.setOnMyLocationButtonClickListener(this);
        Map1.setOnMyLocationClickListener(this);
        if (Map1 == null) {
            Map1.setMyLocationEnabled(true);
        }
        startCurrentLocationUpdates();

        mHandler.postDelayed(new Runnable(){
            public void run(){
                DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
                DatabaseReference uidRef = rootRef.child("Markers");
                Map.clear();
                ValueEventListener valueEventListener = new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        for(DataSnapshot ds: dataSnapshot.getChildren()) {

                            String latitude = ds.child("latitude").getValue().toString();
                            String longitude = ds.child("longitude").getValue().toString();
                            String bus = ds.child("bus_station").getValue().toString();
                            Log.d("TAG", latitude + ", " + longitude);
                            LatLng location = new LatLng(Double.parseDouble(latitude), Double.parseDouble(longitude));

                                Map.addMarker(new MarkerOptions().icon(BitmapDescriptorFactory.fromResource(R.drawable.img_4662878)).position(location).title(bus));
                            }}}}

                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) {
                        Log.d("TAG", databaseError.getMessage()); //Don't ignore errors!
                    }
                };
                uidRef.addListenerForSingleValueEvent(valueEventListener);


                mHandler.postDelayed(this, delay);
            }
        }, delay);
    }}

tell me how to display all markers from the database correctly?

error:

2020-04-22 23:10:12.031 18972-18972/by.sviter.stop E/AndroidRuntime: FATAL EXCEPTION: main
Process: by.sviter.stop, PID: 18972
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.parseDouble(FloatingDecimal.java:110)
    at java.lang.Double.parseDouble(Double.java:538)
    at by.sviter.stoprevizor.tabs.maps.MapsFragment$3$1.onDataChange(MapsFragment.java:337)
    at com.google.firebase.database.Query$1.onDataChange(com.google.firebase:firebase-database@@19.2.1:179)
    at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.1:75)
    at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.1:63)
    at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.1:55)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6718)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:495)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Answer 1

Assuming that dn4O... mgG2 is the uid of the authenticated user, to get the values of the latitude and longitude properties, please use the following lines of code:

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("Markers").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        String latitude = dataSnapshot.child("latitude").getValue(String.class);
        String longitude = dataSnapshot.child("longitude").getValue(String.class);
        Log.d("TAG", latitude + ", " + longitude);
        LatLng location = new LatLng(Double.parseDouble(latitude), Double.parseDouble(longitude));

        //Do what you need to do with the location
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d("TAG", databaseError.getMessage()); //Don't ignore errors!
    }
};
uidRef.addListenerForSingleValueEvent(valueEventListener);

The result in the logat will be:

53.9148950..., 27.4380507...

Edit:

According to your comment:

how to show all the tags?

Please use the following lines of code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference markersRef = rootRef.child("Markers");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String latitude = ds.child("latitude").getValue(String.class);
            String longitude = ds.child("longitude").getValue(String.class);
            Log.d("TAG", latitude + ", " + longitude);
            LatLng location = new LatLng(Double.parseDouble(latitude), Double.parseDouble(longitude));

            //Add the location to a list of locations
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d("TAG", databaseError.getMessage()); //Don't ignore errors!
    }
};
markersRef.addListenerForSingleValueEvent(valueEventListener);

The result in the logcat will be:

// ...
// ...
53.9148950..., 27.4380507...

Answer 2

After the scope of DataSnapshot for loop has ended you can manipulate the contents of the DataModel object using the getters and setters which you should have implemented.

If this does not work. Check if you mMarkers1 object is pointing to the correct class, or change the addListenerForSingleValueEvent to addValueEventListener.

Answer 3

You should you use addValueEventListner instead of addListenerForSingleValueEvent

You must run a for loop to get all data like...

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference(); rootRef.child("Markers").addValueEventListner(new ValueEventListner{

@Override public void onDataChange(DataSnapshot dataSnapshot) { for(DataSnapshot snap: dataSnapshot.getChildern()){ cast into your model class } }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }

});