android - 从 firebase 数据库检索数据的问题

Question

我计划使用 putExtra 将数据从 NearbyActivity (MapsActivity) 传递到 DetailsActivity。但是我遇到了问题，当我启动 NearbyActivity 时，它关闭了。当我检查 NearbyActivity 中存在空指针错误时。你能告诉我哪里出了问题吗？

附近 Activity

  package com.example.rizkafs.laundrize;

    import android.content.Context;
    import android.content.Intent;
    import android.content.pm.PackageManager;
    import android.content.res.Resources;
    import android.location.Criteria;
    import android.location.Location;
    import android.location.LocationManager;
    import android.support.annotation.NonNull;
    import android.support.annotation.Nullable;
    import android.support.v4.app.ActivityCompat;
    import android.support.v4.app.FragmentActivity;
    import android.os.Bundle;
    import android.util.Log;

    import com.google.android.gms.common.ConnectionResult;
    import com.google.android.gms.common.api.GoogleApiClient;
    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.BitmapDescriptor;
    import com.google.android.gms.maps.model.BitmapDescriptorFactory;
    import com.google.android.gms.maps.model.CameraPosition;
    import com.google.android.gms.maps.model.LatLng;
    import com.google.android.gms.maps.model.MapStyleOptions;
    import com.google.android.gms.maps.model.Marker;
    import com.google.android.gms.maps.model.MarkerOptions;
    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;


    public class NearbyActivity extends FragmentActivity implements OnMapReadyCallback {

        private static final String TAG = NearbyActivity.class.getSimpleName();
        public HashMap<Marker, DataLaundry> detailMarkerMap;

        String latitude;
        String longitude;
        String namaTempat;
        String alamat;
        String jenis;
        String harga;
        String jamOperasi;
        String noTelp;

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

        @Override
        public void onMapReady(final GoogleMap googleMap) {

            try {
                // Customise the styling of the base map using a JSON object defined
                // in a raw resource file.
                boolean success = googleMap.setMapStyle(
                        MapStyleOptions.loadRawResourceStyle(
                                this, R.raw.style_json));

                if (!success) {
                    Log.e(TAG, "Style parsing failed.");
                }
            } catch (Resources.NotFoundException e) {
                Log.e(TAG, "Can't find style. Error: ", e);
            }

            googleMap.setMyLocationEnabled(true);


            DatabaseReference myRef = FirebaseDatabase.getInstance().getReference();

            myRef.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    for (DataSnapshot child : dataSnapshot.child("places").getChildren()){
                        latitude = child.child("latitude").getValue(String.class);
                        longitude = child.child("longitude").getValue(String.class);
                        namaTempat = child.child("nama").getValue(String.class);
                        alamat = child.child("alamat").getValue(String.class);
                        jenis = child.child("jenis").getValue(String.class);
                        harga = child.child("harga").getValue(String.class);
                        jamOperasi = child.child("jam_operasional").getValue(String.class);
                        noTelp = child.child("no_telp").getValue(String.class);

                        DataLaundry dataLaundry = new DataLaundry(latitude, longitude, namaTempat, alamat, jenis, harga, jamOperasi, noTelp);

                        LatLng latLng = new LatLng(Double.parseDouble(latitude), Double.parseDouble(longitude));
                        Marker marker = googleMap.addMarker(new MarkerOptions()
                                .position(latLng)
                                .title(namaTempat)
                                .icon(BitmapDescriptorFactory.fromResource(R.drawable.marker))
                                .snippet(jenis));

                        detailMarkerMap.put(marker, dataLaundry);
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

            LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
            Criteria criteria = new Criteria();

            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;
            }
            Location location = locationManager.getLastKnownLocation(locationManager.getBestProvider(criteria, false));
            if(location != null) {
                CameraPosition cameraPosition = new CameraPosition.Builder()
                        .target(new LatLng(location.getLatitude(), location.getLongitude()))
                        .zoom(17)
                        .build();
                googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
            }

            googleMap.setOnInfoWindowClickListener(new GoogleMap.OnInfoWindowClickListener() {
                @Override
                public void onInfoWindowClick(Marker marker) {
                    marker.getTitle();

                    DataLaundry dataLaundry = detailMarkerMap.get(marker);

                    Intent i = new Intent(NearbyActivity.this, DetailsActivity.class);
                    i.putExtra("nama", dataLaundry.getNama());
                    i.putExtra("jenis", dataLaundry.getJenis());
                    i.putExtra("alamat", dataLaundry.getAlamat());
                    i.putExtra("harga", dataLaundry.getHarga());
                    i.putExtra("jam_operasi", dataLaundry.getJamOperasi());
                    i.putExtra("no_telp", dataLaundry.getNoTelp());
                    startActivity(i);
                }
            });
        }
    }

DataLaundry.java

 package com.example.rizkafs.laundrize;

    import com.google.android.gms.maps.model.LatLng;

    /**
     * Created by Abi FS on 6/3/2017.
     */

    public class DataLaundry {

        String nama;
        String alamat;
        String jenis;
        String harga;
        String jamOperasi;
        String no_telp;
        String latitude;
        String longitude;

        public DataLaundry() {
        }

        public DataLaundry(String latitude, String longitude, String nama, String alamat, String jenis, String harga, String jamOperasi, String no_telp) {
            this.latitude = latitude;
            this.longitude = longitude;
            this.nama = nama;
            this.alamat = alamat;
            this.jenis = jenis;
            this.harga = harga;
            this.jamOperasi = jamOperasi;
            this.no_telp = no_telp;
        }

        public String getLatitude() {
            return latitude;
        }

        public void setLatitude(String latitude) {
            this.latitude = latitude;
        }

        public String getLongitude() {
            return longitude;
        }

        public void setLongitude(String longitude) {
            this.longitude = longitude;
        }

        public String getNama() {
            return nama;
        }

        public void setNama(String nama) {
            this.nama = nama;
        }

        public String getAlamat() {
            return alamat;
        }

        public void setAlamat(String alamat) {
            this.alamat = alamat;
        }

        public String getJenis() {
            return jenis;
        }

        public void setJenis(String jenis) {
            this.jenis = jenis;
        }

        public String getHarga() {
            return harga;
        }

        public void setHarga(String harga) {
            this.harga = harga;
        }

        public String getJamOperasi() {
            return jamOperasi;
        }

        public void setJamOperasi(String jamOperasi) {
            this.jamOperasi = jamOperasi;
        }

        public String getNoTelp() {
            return no_telp;
        }

        public void setNoTelp(String no_telp) {
            this.no_telp = no_telp;
        }
    }

详细 Activity

   package com.example.rizkafs.laundrize;

        import android.os.Bundle;
        import android.support.design.widget.FloatingActionButton;
        import android.support.design.widget.Snackbar;
        import android.support.v7.app.AppCompatActivity;
        import android.support.v7.widget.Toolbar;
        import android.view.View;
        import android.widget.TextView;

        public class DetailsActivity extends AppCompatActivity {
            TextView alamat, jenis, harga, jamOperasi, noTelp;

            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_details);
                Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
                setSupportActionBar(toolbar);

                FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
                fab.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                                .setAction("Action", null).show();
                    }
                });

                alamat = (TextView) findViewById(R.id.detail_alamat);
                jenis = (TextView) findViewById(R.id.detail_jenis);
                harga = (TextView) findViewById(R.id.detail_harga);
                jamOperasi = (TextView) findViewById(R.id.detail_jam);
                noTelp = (TextView) findViewById(R.id.detail_notelp);

                setTitle(getIntent().getStringExtra("nama"));
                alamat.setText(getIntent().getStringExtra("alamat"));
                jenis.setText(getIntent().getStringExtra("jenis"));
                harga.setText(getIntent().getStringExtra("harga"));
                jamOperasi.setText(getIntent().getStringExtra("jam_operasi"));
                noTelp.setText(getIntent().getStringExtra("no_telp"));
            }
        }

Android Monitor 错误

    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.util.HashMap.put(java.lang.Object, java.lang.Object)' on a null object reference
            at com.example.rizkafs.laundrize.NearbyActivity$1.onDataChange(NearbyActivity.java:108)
            at com.google.firebase.database.Query$1.onDataChange(Unknown Source)
            at com.google.android.gms.internal.zzbpx.zza(Unknown Source)
            at com.google.android.gms.internal.zzbqx.zzZV(Unknown Source)
            at com.google.android.gms.internal.zzbra$1.run(Unknown Source)
            at android.os.Handler.handleCallback(Handler.java:815)
            at android.os.Handler.dispatchMessage(Handler.java:104)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5847)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1010)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)

Answer 1

您必须初始化 HashMap<Marker, DataLaundry>首先，然后您可以向其中添加值。像这样尝试

HashMap<Marker, DataLaundry> detailMarkerMap = new HashMap<>();

然后使用 detailMarkerMap.put(marker, dataLaundry);在onDataChange(DataSnapshot dataSnapshot)里面