在其他方法中獲取AsyncTask的結果

Question

我想獲得一個servlet作爲文本的響應，來解析此文本並提取在Google地圖上顯示標記的座標。我的問題是，我不知道如何從onMapReady方法中的onPostExecute方法調用結果。就像我在代碼中調用一樣，輸入字符串顯然是空的。

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback { 

private GoogleMap map; 
private static final String LOG_TAG = "ExampleApp"; 
TextView tvIsConnected; 
TextView tvResult; 
TextView textView2; 
private static final String SERVICE_URL = "http://192.168.178.42:8080/TutorialApp/User/GetAll"; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_maps); 
    tvIsConnected = (TextView) findViewById(R.id.tvIsConnected); 
    tvResult = (TextView) findViewById(R.id.tvResult); 
    textView2 = (TextView) findViewById(R.id.textView2); 
    // 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); 
    if (checkNetworkConnection()) 
     // perform HTTP GET request 
     new HTTPAsyncTask().execute("http://192.168.178.42:8080/TutorialApp/User/GetAll"); 
} 


public boolean checkNetworkConnection() { 
    ConnectivityManager connMgr = (ConnectivityManager) 
      getSystemService(Context.CONNECTIVITY_SERVICE); 

    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo(); 
    boolean isConnected = false; 
    if (networkInfo != null && (isConnected = networkInfo.isConnected())) { 
     // show "Connected" & type of network "WIFI or MOBILE" 
     tvIsConnected.setText("Connected " + networkInfo.getTypeName()); 
     // change background color to red 
     tvIsConnected.setBackgroundColor(0xFF7CCC26); 


    } else { 
     // show "Not Connected" 
     tvIsConnected.setText("Not Connected"); 
     // change background color to green 
     tvIsConnected.setBackgroundColor(0xFFFF0000); 
    } 

    return isConnected; 
} 

private static String convertInputStreamToString(InputStream inputStream) throws IOException { 
    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream)); 
    String line = ""; 
    String result = ""; 
    while ((line = bufferedReader.readLine()) != null) 
     result += line + "\n"; 

    inputStream.close(); 
    return result; 

} 
private String HttpGet(String myUrl) throws IOException { 
    InputStream inputStream = null; 
    String result = ""; 

    URL url = new URL(myUrl); 

    // create HttpURLConnection 
    HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 

    // make GET request to the given URL 
    conn.connect(); 

    // receive response as inputStream 
    inputStream = conn.getInputStream(); 

    // convert inputstream to string 
    if (inputStream != null) 
     result = convertInputStreamToString(inputStream); 
    else 
     result = "Did not work!"; 

    return result; 
} 

private class HTTPAsyncTask extends AsyncTask<String, Void, String> { 
    @Override 
    protected String doInBackground(String... urls) { 

     // params comes from the execute() call: params[0] is the url. 
     try { 
      return HttpGet(urls[0]); 
     } catch (IOException e) { 
      return "Unable to retrieve web page. URL may be invalid."; 
     } 
    } 
    //onPostExecute displays the results of the AsyncTask. 
    @Override 
    protected void onPostExecute(String result) { 
     tvResult.setText(result); 
    } 

} 
@Override 
public void onMapReady(GoogleMap googleMap) { 

    String input = tvResult.getText().toString(); 

    String[] lines = input.split("\n"); 
    List<Pair<Double, Double>> list = new ArrayList<>(); 
    String ss="i"; 
    for(int i =1; i < lines.length-1; i++) { 
     int firstcomma = lines[i].indexOf(","); 
     int secondcomma = lines[i].indexOf(",", firstcomma + 1); 
     int thirdcomma = lines[i].indexOf(",", secondcomma + 1); 
     Double lat = Double.parseDouble(lines[i].substring(secondcomma + 1, thirdcomma)); 
     Double longitude = Double.parseDouble(lines[i].substring(thirdcomma + 1, lines.length)); 
     list.add(new Pair(lat,longitude)); 
    } 
    for(int j=1; j<list.size();j++) { 

     map = googleMap; 
     // Add a marker in Sydney and move the camera 
     //LatLng sydney = new LatLng(-34, 151); 
     LatLng sydney = new LatLng(list.get(j).first, list.get(j).second); 
     map.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney")); 
     map.moveCamera(CameraUpdateFactory.newLatLng(sydney)); 
    } 
} 

}

Answer 1

的原因，你不能調用onPostExecute()在onMapReady()的結果，是因爲他們都在後臺運行。您唯一能做的就是致電getMapAsync()從您的onPostExecute()，這將確保您的onPostExecute()已完成;或者將onMapReady()的功能移入onPostExecute()。你基本上有2 asyncTasks運行，所以你需要鏈接它們（這是一種哈克）或將邏輯從onMapReady()移動到onPostExecute()。