java - 为两个 Activity 访问 Asynctask

Question

我有一个 AsyncTask 用于从 API Google Directions 下载路线。该任务从第一个 Activity 开始，我在其中显示用户到某个点的时间和距离，但我的 map 位于第二个 Activity 中，我需要在其中绘制路线。我的问题是如何在两个任务之间维护唯一的下载任务(如果第一个 Activity 中下载尚未完成)，并在两个 Activity 上访问该任务的数据。

public class DownloadDirections {

String urlDownload;
PolylineOptions lineOptions = null;
Context context;
String mTime;
String mDistance;

public DownloadDirections (Context context, String urlDownload){
    this.urlDownload = urlDownload;
    this.context = context;

    new DownloadDirectionsTask().execute(urlDownload);
}

// Fetches data from url passed
private class DownloadDirectionsTask extends AsyncTask<String, Void, String> {

    // Downloading data in non-ui thread
    @Override
    protected String doInBackground(String... url) {

        // For storing data from web service
        String data = "";

        try {
            // Fetching the data from web service
            data = downloadUrl(url[0]);
        } catch (Exception e) {
            Log.d("Background Task", e.toString());
        }
        return data;
    }

    // Executes in UI thread, after the execution of
    // doInBackground()
    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

        ParserTask parserTask = new ParserTask();

        // Invokes the thread for parsing the JSON data
        parserTask.execute(result);

    }
}


/**
 * A method to download json data from url
 */
private String downloadUrl(String strUrl) throws IOException {
    String data = "";
    InputStream iStream = null;
    HttpURLConnection urlConnection = null;
    try {
        URL url = new URL(strUrl);

        // Creating an http connection to communicate with url
        urlConnection = (HttpURLConnection) url.openConnection();

        // Connecting to url
        urlConnection.connect();

        // Reading data from url
        iStream = urlConnection.getInputStream();

        BufferedReader br = new BufferedReader(new InputStreamReader(iStream));

        StringBuffer sb = new StringBuffer();

        String line = "";
        while ((line = br.readLine()) != null) {
            sb.append(line);
        }

        data = sb.toString();

        br.close();

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        iStream.close();
        urlConnection.disconnect();
    }
    return data;
}

/**
 * A class to parse the Google Places in JSON format
 */
private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String, String>>>> {

    // Parsing the data in non-ui thread
    @Override
    protected List<List<HashMap<String, String>>> doInBackground(String... jsonData) {

        JSONObject jObject;
        List<List<HashMap<String, String>>> routes = null;

        try {
            jObject = new JSONObject(jsonData[0]);
            DirectionsJSONParser parser = new DirectionsJSONParser();

            // Starts parsing data
            routes = parser.parse(jObject);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return routes;
    }

    // Executes in UI thread, after the parsing process
    @Override
    protected void onPostExecute(List<List<HashMap<String, String>>> result) {
        ArrayList<LatLng> points = null;
        MarkerOptions markerOptions = new MarkerOptions();
        String distance = "";
        String duration = "";

        if(result != null) {
            if (result.size() < 1) {
                Toast.makeText(context, "No Points", Toast.LENGTH_SHORT).show();
                return;
            }
        }

        if(result != null) {
            // Traversing through all the routes
            for (int i = 0; i < result.size(); i++) {
                points = new ArrayList<LatLng>();
                lineOptions = new PolylineOptions();

                // Fetching i-th route
                List<HashMap<String, String>> path = result.get(i);

                // Fetching all the points in i-th route
                for (int j = 0; j < path.size(); j++) {
                    HashMap<String, String> point = path.get(j);

                    if (j == 0) {    // Get distance from the list
                        distance = (String) point.get("distance");
                        continue;
                    } else if (j == 1) { // Get duration from the list
                        duration = (String) point.get("duration");
                        continue;
                    }

                    double lat = Double.parseDouble(point.get("lat"));
                    double lng = Double.parseDouble(point.get("lng"));
                    LatLng position = new LatLng(lat, lng);

                    points.add(position);
                }

                // Adding all the points in the route to LineOptions
                lineOptions.addAll(points);
                lineOptions.width(2);
                lineOptions.color(Color.RED);
                mTime = duration;
                mDistance = distance;

            }

        }

    }
}

}

Answer 1

有很多选择。

1. 在第一个 Activity 中下载整个项目，将其作为 Intent 数据传递给第二个 Activity ，并在第二个 Activity 中进行访问。如果需要，您可以将数据存储在内部存储(首选项、数据库或文件，具体取决于大小)中，并进行相应的访问。
2. 您想要多次执行该任务(一次又一次):保留对任务对象的引用，并从第二个 Activity 调用中，对第一个 Activity 进行等待调用。
3. 想要使用服务吗？没问题。调用服务，下载数据，如果数据很大则存储它们。如果数据较小，则通过广播传递。在 Activity 中访问它们。

这是你想要的吗？