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AsyncTask with ArrayList as return type

I am trying to return an ArrayList from an AsyncTask. But in main activity i am not able to get the returned arraylist. I want to know the way to call the asynctask so that i can get the returned arraylist.
This is the AsyncTask -
public class GetBannerDB extends AsyncTask<Void, Void, ArrayList<String>> {
GetBannerDB() {
}
#Override
protected ArrayList<String> doInBackground(Void... params) {
InputStream is = null;
ArrayList<String> bannerList = new ArrayList<String>();
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("data", "data"));
try {
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost("url to fetch data");
httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpClient.execute(httpPost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
serverResult = sb.toString().trim();
try {
String sResult = serverResult.substring(0, 7);
if (sResult.equalsIgnoreCase("success")) {
// Creating user login session
// Use user real data
String[] temp = serverResult.split("\\^");
String banner_image = temp[1];
String banner_redirect = temp[2];
bannerList.add(banner_image);
bannerList.add(banner_redirect);
} else {
}
} catch (NullPointerException ex) {
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return bannerList;
}
#Override
protected void onPostExecute(ArrayList<String> result) {
super.onPostExecute(result);
mBannerTask = null;
}
}
In MainActivity, i am calling the output as --
ArrayList<String> adDetails = new ArrayList<>();
mBannerTask = new GetBannerDB();
adDetails = mBannerTask.execute();
But here i am getting error - Incompatible types.
Where m i going wrong pls guide.
Ashok as per your answer, i have done the following changes --
OnDataListener.java (As interface)
public interface OnDataListener {
void setData(ArrayList<String> result);
}
In MainActivity.java -
public class PushAds implements OnDataListener{
String serverResult = null;
private GetBannerDB mBannerTask = null;
ArrayList<String> adDetails = new ArrayList<>();
public void displayAds()
{
mBannerTask = new GetBannerDB(new OnDataListener {
public void setData(ArrayList<String> result){
adDetails = result;
}
});
mBannerTask.execute();
}
......
}
But its giving error.

public interface OnDataListner{
void setData(ArrayList<String> result);
}
and
public class GetBannerDB extends AsyncTask<Void, Void, ArrayList<String>> {
public OnDataListner dataListner;
GetBannerDB(OnDataListner dataListner) {
this.dataListner = dataListner;
}
#Override
protected void onPostExecute(ArrayList<String> result) {
super.onPostExecute(result);
dataListner.setData(result);
}
}
finally
ArrayList<String> adDetails = new ArrayList<>();
mBannerTask = new GetBannerDB(new OnDataListner{
#Overrid
public void setData(ArrayList<String> result){
adDetails = result;
//do something
}
});
mBannerTask.execute();

Cannot resolve symbol 'execute' ... calling AsyncTask

I am trying to make a GET request on a URL, I created a class extending AsyncTask<Void, Void, Void> and I try to call new MyClass.execute() ... I have done this before and it worked, today it is not working. What am I doing wrong?
Here is my code:
public class SignUpActivity extends AppCompatActivity {
String TAG = SignUpActivity.class.getSimpleName();
String URL;
ArrayList<String> countries = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sign_up);
new MyClass.execute();
}
private class MyClass extends AsyncTask<Void, Void, Void> {
#Override
protected void onPreExecute() {
super.onPreExecute();
//TODO
}
#Override
protected Void doInBackground(Void... params) {
HttpHandler sh = new HttpHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(URL, "GET");
//Handling response in jsonStr code
return null;
}
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
//TODO
}
}

This is a syntax error. It should be
new MyClass().execute();
not as new MyClass.execute();

use this to get data use return to return value:
public class SignUpActivity extends AppCompatActivity {
String TAG = SignUpActivity.class.getSimpleName();
String URL;
ArrayList<String> countries = new ArrayList<>();
String jsonStr="";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sign_up);
String response = new MyClass.execute();
}
private class MyClass extends AsyncTask<Void, Void, String> {
#Override
protected void onPreExecute() {
super.onPreExecute();
//TODP
}
#Override
protected String doInBackground(Void... params) {
HttpHandler sh = new HttpHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(URL, "GET");
//Handling response in jsonStr code
return jsonStr;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
//TODO
jsonStr = result;
}
}
}

public class JsonHandler {
static String response = null;
public final static int GET = 1;
public final static int POST = 2;
public JsonHandler() {
}
public String makeServiceCall(String url,int method) {
return this.makeServiceCall(url, method, null);
}
public String makeServiceCall(String url, int method,
List<NameValuePair> params) {
try {
// http client
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpEntity httpEntity = null;
HttpResponse httpResponse = null;
// Checking http request method type
if (method == POST) {
HttpPost httpPost = new HttpPost(url);
if (params != null) {
httpPost.setEntity(new UrlEncodedFormEntity(params));
}
httpResponse = httpClient.execute(httpPost);
} else if (method == GET) {
if (params != null) {
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
}
HttpGet httpGet = new HttpGet(url);
httpResponse = httpClient.execute(httpGet);
}
httpEntity = httpResponse.getEntity();
response = EntityUtils.toString(httpEntity);
} catch (Exception e) {
}
return response;
}
}
Add above class to your main package and do it as doInBackground
#Override
protected Void doInBackground(String... params) {
// TODO Auto-generated method stub
JsonHandler json = new JsonHandler();
String jsonStr = json.makeServiceCall(params[0], JsonHandler.GET);
// parse your json data here
}

Java Interface Callback on Android

I am currently trying to make an android app that basically downloads strings from a url. But I want to make it object oriented. My mainActivity gets string from webService which downloads string when button is clicked. But I am not good at interfaces and callbacks. What should I do to make this code run?
public class MainActivity extends Activity implements WebServiceInterface{
private TextView textView;
private Button readWebPage;
private WebService service;
private WebServiceInterface webServiceInterface;
private String response;
/**
* Called when the activity is first created.
*/
#Override
public void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.TextView01);
readWebPage = (Button) findViewById(R.id.readWebpage);
service = new WebService();
readWebPage.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
service.execute(new String[]{"http://google.com/"});
onSuccess(response);
}
});
}
#Override
public void onSuccess(String response) {
textView.setText(Html.fromHtml(response));
}
#Override
public void onFail(Exception ex) {
textView.setText(ex.getLocalizedMessage());
}
}
public class WebService extends AsyncTask<String, Void, String> {
private WebServiceInterface webServiceInterface;
#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;
}
webServiceInterface.onSuccess(response);
} catch (Exception e) {
e.printStackTrace();
webServiceInterface.onFail(e);
}
}
return response;
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
}
}
public interface WebServiceInterface {
void onSuccess(String response);
void onFail(Exception ex);
}

you need to create one public method for set webServiceInterface in WebService class like
public setWebServiceInterface (WebServiceInterface listener)
{
this.webServiceInterface =listener;
}
in MainActivity activity call this method and pass argument this
service.setWebServiceInterface (this);
in WebService class in onPostExecute Method call
webServiceInterface.onSuccess(s);

Add WebService (WebServiceInterface webServiceInterface) in your AsyncTask as a constructor.
service = new WebService(new WebServiceInterface (){
void onSuccess(String response){
//do your stuff
}
void onFail(Exception ex){
//do your stuff
}
});
and in your asynctask
public class WebService extends AsyncTask<String, Void, String> {
public WebService (WebServiceInterface webServiceInterface){
this.webinterface= webServiceInterface;
}
private WebServiceInterface webinterface;
#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;
}
webinterface.onSuccess(response);
} catch (Exception e) {
e.printStackTrace();
webinterface.onFail(e);
}
}
return response;
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
}
}

I have found the problem, it is because of runOnUiThread is missing.

Bringing back the app to front from a service

Pretty new in Android.
The problem here is simple.
My app needs to be waken up in some interval of time.
The problem is that I can`t call it properly.
There in the comment // HERE IS THE PROBLEM the code is breaking giving me error that cant find context and to declare it.
public class BackgroundService extends Service {
Integer background_connect = null;
String SERVER_IP;
String APP_ID;
private Context context;
#Override
public IBinder onBind(Intent arg0) {
return null;
}
#Override
public void onCreate() {
super.onCreate();
DB_Queries db = new DB_Queries(getApplicationContext());
Cursor c = db.getSettings();
StringBuilder app_id = new StringBuilder();
StringBuilder server_ip = new StringBuilder();
if (c.moveToFirst()) {
do {
server_ip.append(c.getString(c.getColumnIndex("server_ip")));
app_id.append(c.getString(c.getColumnIndex("app_id")));
} while (c.moveToNext());
}
db.close();
SERVER_IP = server_ip.toString();
APP_ID = app_id.toString();
}
#Override
public void onDestroy() {
super.onDestroy();
}
#Override
public int onStartCommand(Intent intent, int flags, int startId) {
requestServerDelay delay = new requestServerDelay();
delay.execute("http://" + SERVER_IP + "/index.php/app/requestAppRecall");
return super.onStartCommand(intent, flags, startId);
}
private class requestServerDelay extends AsyncTask<String, Void, Void> {
#Override
protected Void doInBackground(String... params) {
HttpClient client = new DefaultHttpClient();
HttpPost post = new HttpPost(params[0]);
post.addHeader("Content-type", "application/x-www-form-urlencoded");
List<NameValuePair> pair = new ArrayList<NameValuePair>();
pair.add(new BasicNameValuePair("app_id", APP_ID));
try {
post.setEntity(new UrlEncodedFormEntity(pair));
HttpResponse response = client.execute(post);
InputStream is = response.getEntity().getContent();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
StringBuilder str = new StringBuilder();
String chunk = null;
while ((chunk = br.readLine()) != null) {
str.append(chunk);
}
background_connect = Integer.parseInt(str.toString());
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(Void result) {
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
public void run() {
//HERE IS THE PROBLEM
Intent intent = new Intent(getApplication().getApplicationContext(), getApplication().getApplicationContext().getClass());
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
intent.addFlags(Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED);
intent.addFlags(Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
getApplication().getApplicationContext().startActivity(intent);
}
}, background_connect * 60 * 1000);
}
}
}

If the requestServerDelay task is in the service, you can use getApplicationContext().startActivity(...) to start an activity.
No need for getApplication() before.
Alternatively You can keep a Context member in the Service class (mContext) and use it.

AsyncTask from Activity Class

I am using this class to download txt file
class RetreiveFeedTask extends AsyncTask<String, Void,String> {
#Override
protected ArrayList<Item> doInBackground(String... params) {
try{
URL url = new URL("myurl");
InputStream is = url.openStream();
BufferedReader in = new BufferedReader(new InputStreamReader(is));
String str;
while ((str = in.readLine()) != null){
}
in.close();
return str;
}
catch (MalformedURLException e){}
catch (IOException e){}
return null;
}
protected void onPostExecute(Strin str) {
}
this is how i call this class from my activity:
new RetreiveFeedTask().execute();
And i want to know if there is a way to pass out this result to the activity that make the call.

You can create a listener which you'll pass in the constructor of your AsyncTask. In your onPostExecute you just call this listener.
Something like that:
public interface OnTaskCompleteListener {
void onTaskComplete(String result);
}
protected void onPostExecute(String str) {
onTaskCompleteListener.onTaskComplete(str);
}