使用 AsyncTask 在后台查找城市名称

Question

我的目标是使用 LocationListener 中的坐标获取用户所在城市的名称，并在后台使用 AsyncTask 将其与 Google 的 Maps API 匹配。

当我从 MainActivity (onCreate) 调用 CityFinder 时，什么都没有发生。我没有看到来自 onPreExecute 的任何日志。

我需要做什么来解决这个问题？

CityFinder 异步任务

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.provider.Settings;
import android.util.Log;
import android.widget.Toast;

import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;

import org.json.JSONException;
import org.json.JSONObject;

import static android.support.v4.app.ActivityCompat.requestPermissions;
import static com.android.volley.toolbox.Volley.*;

public class CityFinder extends AsyncTask<Void, Void, Void> {

    private Activity activity;
    private ProgressDialog progressDialog;
    private String googleMapsGeoURL = "http://maps.googleapis.com/maps/api/geocode/json?latlng=";
    private LocationManager locationManager;
    private LocationListener locationListener;
    protected String cityName;

    public CityFinder(Activity activity, LocationManager locationManager, LocationListener locationListener) {
        this.activity = activity;
        this.locationManager = locationManager;
        this.locationListener = locationListener;
        this.progressDialog = new ProgressDialog(this.activity);
    }

    protected void onPreExecute() {
        Log.v("CityFinder", "onPreExecute");
        progressDialog.setMessage("Getting your city's name...");
        progressDialog.show();
        progressDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
            public void onCancel(DialogInterface arg0) {
                CityFinder.this.cancel(true);
            }
        });
    }

    @Override
    protected Void doInBackground(Void... params) {
        try {
            this.locationManager = (LocationManager) this.activity.getSystemService(this.activity.LOCATION_SERVICE);
            this.locationListener = new LocationListener() {
                @Override
                public void onLocationChanged(Location location) {
                    googleMapsGeoURL += location.getLatitude() + "," + location.getLongitude();
                    Log.v("CityFinder", googleMapsGeoURL);
                    final RequestQueue requestQueue = newRequestQueue(activity);
                    JsonObjectRequest request = new JsonObjectRequest(googleMapsGeoURL, null,
                            new Response.Listener<JSONObject>() {
                                @Override
                                public void onResponse(JSONObject response) {
                                    try {
                                        cityName =
                                                response.getJSONArray("results").getJSONObject(0).getString("formatted_address");
                                    } catch (JSONException jex) {
                                    }
                                }
                            }, new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {
                        }
                    });
                    requestQueue.add(request);
                }

                @Override
                public void onStatusChanged(String s, int i, Bundle bundle) {
                }

                @Override
                public void onProviderEnabled(String s) {
                }

                @Override
                public void onProviderDisabled(String s) {
                    activity.startActivity(new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS));
                }
            };
            locationManager.requestLocationUpdates("gps", 1000, 0, locationListener);
        } catch (SecurityException se) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                requestPermissions(this.activity, new String[]{
                        android.Manifest.permission.ACCESS_FINE_LOCATION, android.Manifest.permission.ACCESS_COARSE_LOCATION,
                        android.Manifest.permission.INTERNET}, 9000);
                return null;
            } else {
            }
            Toast.makeText(activity, se.getLocalizedMessage(), Toast.LENGTH_LONG).show();
        }
        return null;
    }

    protected void onPostExecute(Void v) {
        this.progressDialog.setMessage("Your city name has been found: " + this.cityName);
    }
}

Answer 1

创建AsyncTask 后，您错过了execute 调用。有关示例，请参见此文档： https://developer.android.com/reference/android/os/AsyncTask.html

由于您的doInBackground 调用不使用params，您可以简单地运行它：

new CityFinder(this, this.locationManager, this.locationListener).execute();