MainActivity Pelancong1

package mdp.ac.id.pelancong;

import android.content.Intent;
import android.drm.DrmManagerClient;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.view.menu.ListMenuItemView;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.GridView;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    FirebaseAuth mAuth;
    DatabaseReference mRoot, mRef;
    private FirebaseAuth.AuthStateListener mAuthListener;
    String TAG = "MainActivity";
    GridView gvLocation;
    TextView tvNoLocation;
    ProgressBar progressBar;

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

        mRoot = FirebaseDatabase.getInstance().getReference();
        mRef = mRoot.child("locations");

        progressBar = (ProgressBar) findViewById(R.id.progressBar);
        gvLocation = (GridView) findViewById(R.id.gvLocation);
        tvNoLocation = (TextView) findViewById(R.id.tvNoLocation);

        mAuth = FirebaseAuth.getInstance();

        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = firebaseAuth.getCurrentUser();
                if (user != null) {
                    // User is signed in
                    Log.d(TAG, "onAuthStateChanged:signed_in:" + user.getUid());
                } else {
                    // User is signed out
                    Log.d(TAG, "onAuthStateChanged:signed_out");
                    startActivity(new Intent(MainActivity.this, SignInActivity.class));
                    finish();
                }
                // ...
            }
        };

        progressBar.setVisibility(View.VISIBLE);
        fetchLocation();
    }

    private void fetchLocation() {

        mRef.addValueEventListener(new ValueEventListener() {
            List<Location> locationData = new ArrayList<>();
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                Iterator<DataSnapshot> locationSnapshot = dataSnapshot.getChildren().iterator();
                do {
                    HashMap<String, String> locationMap = new HashMap<String, String>();
                    Location location = new Location();
                    String locId = locationSnapshot.next().getKey();
                    Log.d(TAG, "locId: " + locId);
                    location = dataSnapshot.child(locId).getValue(Location.class);
                    Log.d(TAG, "Location name: " + location.getLocName());
                    locationData.add(location);
                } while (locationSnapshot.hasNext());
                progressBar.setVisibility(View.GONE);
                setUI(locationData);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

    private void setUI(List<Location> locations) {
        GridAdapter adapter = new GridAdapter(getApplicationContext(), locations);
        gvLocation.setAdapter(adapter);
    }

    @Override
    protected void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(mAuthListener);
    }

    @Override
    protected void onStop() {
        super.onStop();
        if (mAuthListener != null) {
            mAuth.removeAuthStateListener(mAuthListener);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id == R.id.action_sign_out) {
            mAuth.signOut();
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}