如何通过改造来填充数组列表

Question

我有一个返回一些数据的服务，例如，我已经可以获取此数据并并置在文本视图或日志/祝酒中，但是我想将其包含在ArrayList中以供Google地图读取，但是我尝试了，正在显示错误。 下面的代码和错误

主要活动。

@Override
public void onMapReady(GoogleMap googleMap) {

        mMap = googleMap;
        // create class object
        gps = new GPSTracker(MainActivity.this);

       this.getOccurrence();

        // check if GPS enabled
        if(gps.canGetLocation()){

            double latitude = gps.getLatitude();
            double longitude = gps.getLongitude();


            LatLng local = new LatLng(latitude, longitude);
            mMap.addMarker(new MarkerOptions().position(local));
            mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(local, 16));

            // Create a heat map tile provider, passing it the lat long of the police stations.
            mProvider = new HeatmapTileProvider.Builder()
                    .data(list) // Error happens here
                    .build();
            // Add a tile overlay to the map, using the heat map tile provider.
            mOverlay = mMap.addTileOverlay(new TileOverlayOptions().tileProvider(mProvider));

        }else{
            gps.showSettingsAlert();
        }


    private void getOccurrence() {
        try {
            list = readItems();
        } catch (JSONException e) {
            Toast.makeText(this, "Error", Toast.LENGTH_LONG).show();
        }

    }


    private List<LatLng> readItems() throws JSONException {
    ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);
    final Call<List<MyPojo>> call = apiService.getResut();
    call.enqueue(new Callback<List<MyPojo>>() {
        @Override
        public void onResponse(Call<List<MyPojo>> call, Response<List<MyPojo>> response) {

            try {
                List<MyPojo> LatLngData = response.body();
                Log.v(TAG, "LOGS" + LatLngData.size());
                ArrayList<LatLng> list = new ArrayList<LatLng>();
                for (int i = 0; i < LatLngData.size(); i++) {
                    double lat = LatLngData.get(i).getLat();
                    double lng = LatLngData.get(i).getLng();
                    list.add(new LatLng(lat, lng));
                }

            } catch (Exception e) {
                Log.d("onResponse", "There is an error");
                e.printStackTrace();
            }
        }
        @Override
        public void onFailure(Call<List<MyPojo>> call, Throwable t) {

        }
    });
    Log.v(TAG, "" + list);
    return list;
}

MyPojo（型号）

import com.google.gson.annotations.SerializedName;

public class MyPojo {

    @SerializedName("lat")
    private Double lat;

    @SerializedName("lng")
    private Double lng;

    public MyPojo(Double lat, Double lng) {
        this.lat = lat;
        this.lng = lng;
    }


    public Double getLat() {
        return lat;
    }

    public void setLat(Double lat) {
        this.lat = lat;
    }

    public Double getLng() {
        return lng;
    }

    public void setLng(Double lng) {
        this.lng = lng;
    }
}

ApiInterface

public interface ApiInterface {

    @Headers("Accept: application/json")
    @GET("/locations")
    Call<List<MyPojo>> getResult();

}

错误

1

2-08 14:13:53.348 3823-3823/
  br.com.example E/AndroidRuntime: FATAL EXCEPTION: main
                                                                      Process: br.com.example, PID: 3823
                                                                      java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.util.Collection.iterator()' on a null object reference
                                                                          at br.com.example.googlemaps.heatmaps.HeatmapTileProvider.wrapData(HeatmapTileProvider.java:346)
                                                                          at br.com.example.googlemaps.heatmaps.HeatmapTileProvider.access$000(HeatmapTileProvider.java:39)
                                                                          at br.com.example.googlemaps.heatmaps.HeatmapTileProvider$Builder.data(HeatmapTileProvider.java:188)
                                                                          at br.com.example.activity.MainActivity.onMapReady(MainActivity.java:140)
                                                                          at com.google.android.gms.maps.SupportMapFragment$zza$1.zza(Unknown Source)
                                                                          at com.google.android.gms.maps.internal.zzo$zza.onTransact(Unknown Source)
                                                                          at android.os.Binder.transact(Binder.java:499)
                                                                          at yd.a(:com.google.android.gms.DynamiteModulesB:82)
                                                                          at maps.ad.t$5.run(Unknown Source)
                                                                          at android.os.Handler.handleCallback(Handler.java:751)
                                                                          at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                          at android.os.Looper.loop(Looper.java:154)
                                                                          at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                                          at java.lang.reflect.Method.invoke(Native Method)
                                                                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

Answer 1

ApiInterface

public interface ApiInterface {

    @Headers("Accept: application/json")
    @GET("/locations")
    Call<ArrayList<MyPojo>> getResult();

}

希望您已经为gson转换器添加了这样的改造

addConverterFactory(GsonConverterFactory.create())

初始化你的数组列表

ArrayList<MyPojo> latLngData = new ArrayList<MyPojo>()

像下面那样改变你的方法

private ArrayList<LatLng> readItems() throws JSONException {
    ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);
    final Call<ArrayList<MyPojo>> call = apiService.getResut();
    call.enqueue(new Callback<ArrayList<MyPojo>>() {
        @Override
        public void onResponse(Call<ArrayList<MyPojo>> call, Response<ArrayList<MyPojo>> response) {

            try {
                latLngData.addAll(response.body()) ;
                Log.v(TAG, "LOGS" + LatLngData.size());
                ArrayList<LatLng> list = new ArrayList<LatLng>();
                for (int i = 0; i < latLngData.size(); i++) {
                    double lat = latLngData.get(i).getLat();
                    double lng = latLngData.get(i).getLng();
                    list.add(new LatLng(lat, lng));
                }

            } catch (Exception e) {
                Log.d("onResponse", "There is an error");
                e.printStackTrace();
            }
        }
        @Override
        public void onFailure(Call<ArrayList<MyPojo>> call, Throwable t) {

        }
    });
    Log.v(TAG, "" + list);
    return list;
}

而在这种方法

  private void getOccurrence() {
        try {
            list = readItems();
        } catch (JSONException e) {
            Toast.makeText(this, "Error", Toast.LENGTH_LONG).show();
        }

    }

确保list已声明并初始化为ArrayList

让我知道这是否适合您。

Answer 2

initialized ArrayList 

        private List<LatLng> readItems() throws JSONException {
    List<LatLng> list=new List<>();
        ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);
        final Call<List<MyPojo>> call = apiService.getResut();
        call.enqueue(new Callback<List<MyPojo>>() {
            @Override
            public void onResponse(Call<List<MyPojo>> call, Response<List<MyPojo>> response) {

                try {
                    List<MyPojo> LatLngData = response.body();
                    Log.v(TAG, "LOGS" + LatLngData.size());
                    ArrayList<LatLng> list = new ArrayList<LatLng>();
                    for (int i = 0; i < LatLngData.size(); i++) {
                        double lat = LatLngData.get(i).getLat();
                        double lng = LatLngData.get(i).getLng();
                        list.add(new LatLng(lat, lng));
                    }

                } catch (Exception e) {
                    Log.d("onResponse", "There is an error");
                    e.printStackTrace();
                }
            }
            @Override
            public void onFailure(Call<List<MyPojo>> call, Throwable t) {

            }
        });
        Log.v(TAG, "" + list);
        return list;
    }