在Android中管理多个异步任务

Question

大家好，我只是开始在线培训应用程序的第二部分，并尝试调整异步任务以从电影数据库获得电影评论。 为此，有一个完全不同的异步任务似乎应该有一个更好的方法。 这是当前仅获取电影数据的异步任务实现。

问题是我如何在此添加另一个异步任务，以便也可以从此URL / movie / {id} / videos中检索电影评论。

public FetchMovieData(Context context, GridView grid, boolean sortType, ITaskCompleteListener listener) {
    mContext = context;
    this.mMoviesGrid = grid;
    this.mSortByMostPopular = sortType;
    this.mTaskCompleteListener = listener;
}

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

    // These two need to be declared outside the try/catch
    // so that they can be closed in the finally block.
    HttpURLConnection urlConnection = null;
    BufferedReader reader = null;

    try {
        URL url;
        if(mSortByMostPopular)
            url = new URL(mContext.getString(R.string.picasso_url_popular_movies));
        else
            url = new URL(mContext.getString(R.string.picasso_url_highest_rated));

        // Create the request to OpenWeatherMap, and open the connection
        urlConnection = (HttpURLConnection) url.openConnection();
        urlConnection.setRequestMethod("GET");
        urlConnection.connect();

        // Read the input stream into a String
        InputStream inputStream = urlConnection.getInputStream();
        StringBuffer buffer = new StringBuffer();
        if (inputStream == null) {
            // Nothing to do.
            mMovieJsonStr = null;
        }
        reader = new BufferedReader(new InputStreamReader(inputStream));

        String line;
        while ((line = reader.readLine()) != null) {
            // Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
            // But it does make debugging a *lot* easier if you print out the completed
            // buffer for debugging.
            buffer.append(line + "\n");
        }

        if (buffer.length() == 0) {
            // Stream was empty.  No point in parsing.
            mMovieJsonStr = null;
        }
        mMovieJsonStr = buffer.toString();
    } catch (IOException e) {
        Log.e("PlaceholderFragment", "Error ", e);
        // If the code didn't successfully get the weather data, there's no point in attempting
        // to parse it.
        mMovieJsonStr = null;
    } finally {
        if (urlConnection != null) {
            urlConnection.disconnect();
        }
        if (reader != null) {
            try {
                reader.close();
            } catch (final IOException e) {
                Log.e("PlaceholderFragment", "Error closing stream", e);
            }
        }
    }

    return null;
}

@Override
protected void onPostExecute(Void aVoid) {
    super.onPostExecute(aVoid);
    if(mMovieJsonStr != null)
        Constants.mMovies = MovieDataParser.getMovieData(mMovieJsonStr);

    mTaskCompleteListener.onTaskCompleted(); //Task completed alert UI that we have our data
}

因此，有人建议使用Retrofit而不是执行多个异步任务。 这似乎是个好主意，但我在理解其工作方式时遇到了很多麻烦。 目前，我有一个WebService类的接口，并试图使用它来检索电影和影片，​​然后添加评论，然后预告片。 问题是，如果我将基本URL设置为“ http://api.themoviedb.org ”，我得到的URL必须在logcat中以“ /”开头。

当前代码：

public class WebService {
  public List<Movie> getMovies() {

    RestAdapter retrofit = new RestAdapter.Builder()
            .setEndpoint("http://api.themoviedb.org")
            .build();

    MovieDBService service = retrofit.create(MovieDBService.class);

    return service.listMovies("movies");
   }
 }

public interface MovieDBService {
                     @GET("/3/discover/{switchterm}sort_by=popularity.desc&api_key=d273a1a1fb9390dab9  7ac0032b12366a")

  List listMovies(@Path("switchterm") String switchterm);
}

//In code getting movies
WebService service = new WebService();
List movies = service.getMovies();

Answer 1

我认为您有很多方法可以执行此操作。您可以遵循这种方法：在第一个调用完成时向另一个AsyncTask添加第二个调用，并将带有视频ID的字符串列表传递给它：

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

    protected Boolean doInBackground() {
       try {
           String movieJSONString = getJSONMovies();
           String[] ids = parseIdsFromJSON(movieJSONString);
           if(ids.lenth != 0) {
               FetchMovieReviews moviesReviewsAsyncTask = new FetchMovieReviews();
               moviesReviewsAsyncTask.execute(ids);
           } else {
               return false;
           }

           return true;
        } catch (Exception e) {
           return false;
        }
    }

    protected String getJSONMovies() {
       //with the code you post, return the json string
    }

    protected String[] parseIdsFromJSON(String JSON) {
        //parse the json and get the ids and return
        //return {"1","2","3"}
    }
}

public class FetchMovieReviews extends AsyncTask<String[], Void, Void> {

    protected Void doInBackground(String[]... params) {
       for(String id : params[0]) {
           //call the web service and pass the id
       }

       return null;
    }
}

您可以将所有功能（用于管理对Web服务的调用）放在MoviesRESTCalls类中，并将管理json放在MoviesJSONParser类或类似的东西中，并且代码将更加清晰。

Answer 2

因此，我最终使用的是针对Web服务的Retrofit库。 感谢大家的帮助，让我知道您的想法。

public Context mContext;
private MovieJSON mMovieData;
private ReviewJSON mMovieReviews;
private VideoJSON mMovieVideos;
public boolean mSortByMostPopular;
ITaskCompleteListener mTaskCompleteListener;

public FetchMovieData(Context context, boolean sortType, ITaskCompleteListener listener) {
    mContext = context;
    this.mSortByMostPopular = sortType;
    this.mTaskCompleteListener = listener;
}

public void getMovies() {
    new FetchMovies().execute();
}

public void getReviews() {
    new FetchReviews().execute();
}

public void getVideos() {
    new FetchTrailers().execute();
}

private class FetchMovies extends AsyncTask<String, Void, Void > {

    @Override
    protected Void doInBackground(String... params) {
        WebService service = new WebService();
        //TODO Re-Implement sorting
        mMovieData = service.getMovies();
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        if(mMovieData != null)
            Constants.mMovies = MovieDataParser.getMovieData(mMovieData);

        mTaskCompleteListener.onTaskCompleted(); //Task completed alert UI that we have our data
    }
}

private class FetchReviews extends AsyncTask<String, Void, Void > {

    @Override
    protected Void doInBackground(String... params) {
        WebService service = new WebService();
        mMovieReviews = service.getReviews();
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        if(mMovieReviews != null)
            Constants.mReviews = MovieDataParser.getReviewData(mMovieReviews);

        mTaskCompleteListener.onTaskCompleted(); //Task completed alert UI that we have our data
    }
}

private class FetchTrailers extends AsyncTask<String, Void, Void > {

    @Override
    protected Void doInBackground(String... params) {
        WebService service = new WebService();
        mMovieVideos = service.getVideos();
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        if(mMovieVideos != null)
            Constants.mTrailers = MovieDataParser.getVideoData(mMovieVideos);

        mTaskCompleteListener.onTaskCompleted(); //Task completed alert UI that we have our data
    }
}

//网络服务

公共类WebService {

RestAdapter mRetrofit;

MovieDBService mService;

public WebService() {
    mRetrofit = new RestAdapter.Builder()
            .setEndpoint("http://api.themoviedb.org")
            .build();
    mService = mRetrofit.create(MovieDBService.class);
}

public MovieJSON getMovies() {
    return mService.listMovies("");
}

public ReviewJSON getReviews() {
    return mService.listReviews("76341");
}

public VideoJSON getVideos() {
    return mService.listVideos("76341");
}

}