android - mapsActivity异步方法获取JSON

Question

我创建了一个基本的 mapsActivity，我想从 JSON 字符串中获取坐标。我用于从服务器获取 JSON 字符串的方法是异步的，因此当我使用调试工具时我的 JSON 字符串显示为空。

我看到 onActivityResult 可以帮助解决我的问题，但是当我键入“@Override”时，它说“方法不覆盖其父类(super class)中的方法”。我应该怎么做才能使用 MapsActivity 中的数据获取我的 JSON 字符串？

MapsActivity.java

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

private GoogleMap mMap;

String json_string; //ici seront stockées les information concernant les établissements

protected static String JSON_STRING;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);
    // 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
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == 1 && resultCode == RESULT_OK){
        json_string = data.getStringExtra("JSON_string");
    }
}

@Override
public void onMapReady(GoogleMap googleMap) {



    Intent myIntent = new Intent(this, getJSON.class);
    startActivityForResult(myIntent, 1);


    /*
    LatLng flams = new LatLng(47.221626, -1.557679);
    mMap.addMarker(new MarkerOptions().position(flams).title("Le flams"));
    mMap.moveCamera(CameraUpdateFactory.newLatLng(flams));*/
}

getJSON.java

public class getJSON extends AppCompatActivity {

String json_string;
protected static String JSON_STRING; //string for both getJSON and mapsActivity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

        new BackgroundTask().execute();

}


public class BackgroundTask extends AsyncTask<Void, Void, String> {


    String json_url = "the URL of my server";

    @Override
    protected String doInBackground(Void... voids) {

        try {
            URL url = new URL(json_url);
            HttpURLConnection httpURLConnection =(HttpURLConnection) url.openConnection();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            StringBuilder stringBuilder = new StringBuilder();

            while ((json_string = bufferedReader.readLine()) != null){
                stringBuilder.append(json_string+"\n");
            }

            bufferedReader.close();
            inputStream.close();
            httpURLConnection.disconnect();
            return stringBuilder.toString().trim(); <= while this shows the data

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

       public BackgroundTask() {
        super();
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(String result) {
        JSON_STRING=result;
        Intent intent = new Intent();
        intent.putExtra("JSON_string", JSON_STRING);
        setResult(RESULT_OK, intent);
        finish();
    }

Answer 1

根据您的代码，当您启动 Activity getJSON 时，从服务器端获取数据需要时间，这就是您无法立即获取 json_string 的值的原因。顺便说一句，请按照我的指导正确制作逻辑。

当一个Activity startActivityForResult 然后会在onActivityResult 方法中得到结果。

在您的代码中，当您启动 Activity getJSON 时，需要将 JSON_STRING 发送回 mapsActivity，如下代码所示:

   Intent intent = new Intent();
   intent.putExtra("JSON_string", JSON_STRING);
   setResult(RESULT_OK, intent);
   finish();

您将在 mapsActivity 中的方法 onActivityResult 中获得结果:

   @Override
   protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
      super.onActivityResult(requestCode, resultCode, data);
      if (requestCode == 1 && resultCode == RESULT_OK){
         json_string = data.getStringExtra("JSON_string");
      }
   }

有什么不明白的可以问我。