java - 如何从其他类(即 Activity 类)内的(AsyncTask)获取列表值？

Question

当我想从 AsyncTask 类中的全局变量获取值时遇到问题。我想从另一个类调用它..

这是我的 AsyncTask 类代码:

public class PlacesDisplayTask extends AsyncTask<Object, Integer, List<HashMap<String, String>>> {

    List<NearbyPlaceModel> data_place = new ArrayList<>();
    JSONObject googlePlacesJson;
    GoogleMap googleMap;

    @Override
    protected List<HashMap<String, String>> doInBackground(Object... inputObj) {

        List<HashMap<String, String>> googlePlacesList = null;
        Places placeJsonParser = new Places();

        try {
            googleMap = (GoogleMap) inputObj[0];
            googlePlacesJson = new JSONObject((String) inputObj[1]);
            googlePlacesList = placeJsonParser.parse(googlePlacesJson);
        } catch (Exception e) {
            Log.d("Exception", e.toString());
        }
        return googlePlacesList;
    }

    @Override
    protected void onPostExecute(List<HashMap<String, String>> list) {
        googleMap.clear();
        data_place.clear();
        for (int i = 0; i < list.size(); i++) {
            if(i < 10 ) {
                HashMap<String, String> googlePlace = list.get(i);
                double lat = Double.parseDouble(googlePlace.get("lat"));
                double lng = Double.parseDouble(googlePlace.get("lng"));
                String placeName = googlePlace.get("place_name");
                String vicinity = googlePlace.get("vicinity");
                LatLng latLng = new LatLng(lat, lng);
                markerOptions.icon(BitmapDescriptorFactory.fromBitmap(Configure.getBitmapFromURL(googlePlace.get("icon"))));
                markerOptions.title(placeName + " : " + vicinity);
                googleMap.addMarker(markerOptions);

                NearbyPlaceModel items = new NearbyPlaceModel();
                items.setVicinity(vicinity);
                items.setPlace_name(placeName);
                items.setLat(String.valueOf(lat));
                items.setLang(String.valueOf(lng));
                data_place.add(items);
            }
        }
    }

}

我想设置全局变量data_place = new ArrayList<>();来自另一个类(class)，这是我的 Activity ，就像这样..

ListView nearby_place = (ListView) findViewById(R.id.itemListView);
    ListAdapter customAdapter = new ListAdapter(this, R.layout.nearby_place_listview, data_place);
    nearby_place.setAdapter(customAdapter);

或者我的代码有问题吗..？

Answer 1

您可以通过接口(interface)获取结果。

1. 创建具有所需回调方法的接口(interface)。
2. 在您的 Activity 中实现它，
3. 您将通过回调方法获得结果

这里我根据您的代码给您一个示例。 你的 MainActivity 类应该是这样的 -

 public class MainActivity extends AppCompatActivity implements PlaceInterface{

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

         // your code...

         // calling the AsyncTask and send reference of the interface on it
         new PlacesDisplayTask(this).execute();  // something like this

     }


     @Override
     public void myPlaceList(ArrayList<NearbyPlaceModel>   nearbyPlaceModelArrayList) {
         ListView nearby_place = (ListView)  findViewById(R.id.itemListView);
         ListAdapter customAdapter = new ListAdapter(this, R.layout.nearby_place_listview, nearbyPlaceModelArrayList);
         nearby_place.setAdapter(customAdapter);
     }
}

你的 PlacesDisplayTask 类应该是这样的-

 public class PlacesDisplayTask extends AsyncTask<Object, Integer, List<HashMap<String, String>>> {

     ArrayList<NearbyPlaceModel> data_place = new ArrayList<>();   // change
     JSONObject googlePlacesJson;
     GoogleMap googleMap;
     PlaceInterface placeInterface;    // change

     public PlacesDisplayTask(PlaceInterface placeInterface){   // change
         this.placeInterface = placeInterface;
     }

     @Override
     protected List<HashMap<String, String>> doInBackground(Object... inputObj) {

         List<HashMap<String, String>> googlePlacesList = null;
         Places placeJsonParser = new Places();

         try {
             googleMap = (GoogleMap) inputObj[0];
             googlePlacesJson = new JSONObject((String) inputObj[1]);
             googlePlacesList = placeJsonParser.parse(googlePlacesJson);
         } catch (Exception e) {
             Log.d("Exception", e.toString());
         }
         return googlePlacesList;
     }

     @Override
     protected void onPostExecute(List<HashMap<String, String>> list) {
         googleMap.clear();
         data_place.clear();
         for (int i = 0; i < list.size(); i++) {
             if(i < 10 ) {
                 HashMap<String, String> googlePlace = list.get(i);
                 double lat = Double.parseDouble(googlePlace.get("lat"));
                 double lng = Double.parseDouble(googlePlace.get("lng"));
                 String placeName = googlePlace.get("place_name");
                 String vicinity = googlePlace.get("vicinity");
                 LatLng latLng = new LatLng(lat, lng);
             markerOptions.icon(BitmapDescriptorFactory.fromBitmap(Configure.getBitmapFromURL(googlePlace.get("icon"))));
                 markerOptions.title(placeName + " : " + vicinity);
                 googleMap.addMarker(markerOptions);

                 NearbyPlaceModel items = new NearbyPlaceModel();
                 items.setVicinity(vicinity);
                 items.setPlace_name(placeName);
                 items.setLat(String.valueOf(lat));
                 items.setLang(String.valueOf(lng));
                 data_place.add(items);

                 placeInterface.myPlaceList(data_place);  // change
             }
         }
     }

 }

这就是界面-

 public interface PlaceInterface {
     void myPlaceList(ArrayList<NearbyPlaceModel> nearbyPlaceModelArrayList);
 }

希望这对您有帮助。 :)