在AsyncTask中使用setter方法onPostExecute

Question

My onPostExecute method needs to return a result back to onCreate() so it can do stuff with it but I'm struggling to get there.

public class ScheduleList extends Activity {

    public String url = "http://www.bbc.co.uk/bbcnews/programmes/schedules/today.json";

    private DownloadJSON mTask = null;


    public static String fetchedJSON = "";
    public static String getFetchedJSON() {
       return fetchedJSON;
    }
  public static void setFetchedJSON(String fetchedJSON) {
     ScheduleList.fetchedJSON = fetchedJSON;
  }


@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_schedule_list);

    // Show the Up button in the action bar.
    setupActionBar();

    TextView tvNotice = (TextView) findViewById(R.id.schedulePreamble);
    tvNotice.setText("Well, hello there...");

    System.out.println("Hello");
    downloadPage();
    System.out.println(getFetchedJSON());

}


public class DownloadJSON extends AsyncTask<String, Integer, String> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);

    }

    @Override
    protected String doInBackground(String... urls) {
        String response = "";
        for (String url : urls) {
            DefaultHttpClient client = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(url);
            try {
                HttpResponse execute = client.execute(httpGet);
                InputStream content = execute.getEntity().getContent();

                BufferedReader buffer = new BufferedReader(new InputStreamReader(
                        content));
                String s = "";
                while ((s = buffer.readLine()) != null) {
                    response += s;
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return response;
    }

    @Override
    public void onPostExecute(String result) {
        setFetchedJSON(result);
    }


}

private void downloadPage() {
    if (mTask != null && mTask.getStatus() != DownloadJSON.Status.FINISHED) {
        mTask.cancel(true);
    }
    mTask = (DownloadJSON) new DownloadJSON().execute(new String[] { url });
}

}

Every time I run the code, System.out.println(getFetchedJSON()); returns nothing which means my onPostExecute hasn't actually changed the contents of any variable at all, has it?

Answer 1

I have modified my code.This code will get your JSON from Url and convert it into a String and a Json Objecct This will work now

public class MainActivity extends Activity {
InputStream is = null;
JSONObject jObj = null;
String json = "";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button b = (Button) findViewById(R.id.button1);

    b.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            // Making HTTP request
            try {
                StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();

                StrictMode.setThreadPolicy(policy); 
                // defaultHttpClient
                String url = "http://api.androidhive.info/contacts/";
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();           

            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            try {
                BufferedReader reader = new BufferedReader(new InputStreamReader(
                        is, "iso-8859-1"), 8);
                StringBuilder sb = new StringBuilder();
                String line = null;
                while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
                }
                is.close();
                json = sb.toString();
            } catch (Exception e) {
                Log.e("Buffer Error", "Error converting result " + e.toString());
            }

            // try parse the string to a JSON object
            try {
                jObj = new JSONObject(json);
            } catch (JSONException e) {
                Log.e("JSON Parser", "Error parsing data " + e.toString());
            }

            // return JSON String

        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

Add this line in Android Manifest :-

    <uses-permission android:name="android.permission.INTERNET" />

Answer 2

The method downloadPage() launch your task. This task is executed in other thread and immediately after you launch your task you want to print the result but the task is not over yet. Try this code :

public class ScheduleList extends Activity {

 public String url = "http://www.bbc.co.uk/bbcnews/programmes/schedules/today.json"; private DownloadJSON mTask = null; public static String fetchedJSON = ""; public static String getFetchedJSON() { return fetchedJSON; } public static void setFetchedJSON(String fetchedJSON) { ScheduleList.fetchedJSON = fetchedJSON; } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_schedule_list); // Show the Up button in the action bar. setupActionBar(); TextView tvNotice = (TextView) findViewById(R.id.schedulePreamble); tvNotice.setText("Well, hello there..."); System.out.println("Hello"); downloadPage(); } public void printFetchedJSON() { System.out.println(getFetchedJSON()); } public class DownloadJSON extends AsyncTask<String, Integer, String> { @Override protected void onPreExecute() { super.onPreExecute(); } @Override protected void onProgressUpdate(Integer... values) { super.onProgressUpdate(values); } @Override protected String doInBackground(String... urls) { String response = ""; for (String url : urls) { DefaultHttpClient client = new DefaultHttpClient(); HttpGet httpGet = new HttpGet(url); try { HttpResponse execute = client.execute(httpGet); InputStream content = execute.getEntity().getContent(); BufferedReader buffer = new BufferedReader(new InputStreamReader( content)); String s = ""; while ((s = buffer.readLine()) != null) { response += s; } } catch (Exception e) { e.printStackTrace(); } } return response; } @Override public void onPostExecute(String result) { setFetchedJSON(result); printFetchedJSON(); } } private void downloadPage() { if (mTask != null && mTask.getStatus() != DownloadJSON.Status.FINISHED) { mTask.cancel(true); } mTask = (DownloadJSON) new DownloadJSON().execute(new String[] { url }); } 

}