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android code doesn't work when I added threads

I am writing an android application, I previously had a problem NetworkOnMainThreadException and I solved using threads. I now don't get any error and also I don't get any output.
here is my code: there is no errors in the LogCat
public class Currency_convert extends Activity {
public int to;
public int from;
public String [] val;
public String s;
public Handler handler;
public double am=0.0;
StringBuilder build=null ;
HttpClient client=null;
HttpGet httpGet =null;
HttpResponse response=null;
HttpEntity entity=null;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.currency);
Spinner s1 = (Spinner) findViewById(R.id.spinner11);
Spinner s2 = (Spinner) findViewById(R.id.spinner22);
final EditText e=(EditText) findViewById(R.id.amountt);
// am=Double.parseDouble(e.getText().toString());
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.name, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.select_dialog_singlechoice);
val = getResources().getStringArray(R.array.value);
s1.setAdapter(adapter);
s2.setAdapter(adapter);
s1.setOnItemSelectedListener(new spinOne(1));
s2.setOnItemSelectedListener(new spinOne(2));
Button b = (Button) findViewById(R.id.button11);
b.setOnClickListener(new OnClickListener(){
public void onClick(View v) {
TextView t = (TextView) findViewById(R.id.textView44);
if(from == to) {
Toast.makeText(getApplicationContext(), "Invalid", 4000).show();
}
else {
try {
s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+val[from]+val[to]+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");
//s=getJson("http://www.google.com/ig/calculator?hl=en&q=1USD=?INR");
JSONObject jObj;
jObj = new JSONObject(s);
String exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");
am=Double.parseDouble(e.getText().toString());
double totalR=(Double.parseDouble(exResult))*am;
String r=String.valueOf(totalR);
t.setText(r);
// Log.println(priority, tag, msg)
System.out.println("r =" +r);
Log.i("hello", r);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
});
}
public String getJson(final String url)throws ClientProtocolException, IOException {
// private String getJson(String url)throws ClientProtocolException, IOException e {
build = new StringBuilder();
client = new DefaultHttpClient();
httpGet = new HttpGet(url);
new Thread(new Runnable() {
public void run() {
try {
response = client.execute(httpGet);
entity = response.getEntity();
InputStream content = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(content));
String con;
while ((con = reader.readLine()) != null) {
build.append(con);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
// response = client.execute(httpGet);
// entity = response.getEntity();
// InputStream content = entity.getContent();
// BufferedReader reader = new BufferedReader(new InputStreamReader(content));
// String con;
// while ((con = reader.readLine()) != null) {
// build.append(con);
// }
return build.toString();
//return url;
}
private class SpinOne implements OnItemSelectedListener {
int ide;
SpinOne(int i) {
ide =i;
}
public void onItemSelected(AdapterView<?> parent, View view,
int index, long id) {
if(ide == 1) {
from = index;
}
else if(ide == 2) {
to = index;
}
}
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
}}

The way it is written, getJson() will return immediately without giving time for the thread to run completely, so the returned value will not be what you want. Use an AsyncTask so you can run your thread code in the AsyncTask's doInBackground() method and then pass the result to the onPostExecute() method where you can then perform setText() as you intend.
An alternative is to move the JSON parsing and setText() code into the thread's run() method after the HTTP request is made but since running UI-related code (in this case setText()) in a separate thread is not allowed you can use a Handler to schedule setText() to run in the UI thread.
You can read the basics on AsyncTask and Handler here.

When you spawn a thread, code execution splits into different time frames, so even though global scope is shared, you won't get objects populated in a timely fashion for your UI update task if you don't implement some logic to prevent inconsistencies.
Android provides multiple flow control and inter-thread communication patterns built-in that can help you solve such inconsistencies. One such option involves AsyncTask, in your case you can do the following:
Extended AsyncTask with your UI thread-forbidden tasks inside the doInBackground() method;
Get logic that needs to run on UI thread (such as manipulating Views) inside onPostExecute() handler from the same AsyncTask instance. This handler will only be called after doInBackground returns, so the program knows that the logic to populate the object was triggered.
You can look up a sample of AsyncTask in this answear for a practical approach.
Note: If you want to use parent class members such as findViewByID inside an AsyncTask instance, you will need to manually invoke the parent file scope using the <UIThreadName>.this., e.g. <UIThreadName>.this.findViewByID(id). You can do this freely in onPostExecute which has no restrictions due to running on the UI thread, but you are restricted to not performing UI changes in doInBackground (which doesn't run on the UI thread).

I solved it, I just added t.join after the thread declaration :)

App needs to get JSON and display it. How to do it using async thread?

As mentioned I get the above error which I know is because my application is doing networking in UI thread. I went through a lot of stackoverflow questions which advise to use AsyncTask for this purpose. From what I understand asynctask is asynchronous and will run independently in the background. But I need to fetch the data from http and display on the main thread. So basically my UI thread should be blocked till I have the JSON fetched so that I can display it.
My questions are
1) Since I need to run http networking in another thread how do I do it?
2) Do I use an async thread?
3) How do I block my UI thread for the async thread to fetch the result?
4) How do I pass the result from async thread back to UI thread?
This is the current JSON parser class that I use.
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
public JSONArray getJSONfromURL(String url) {
// initialize
InputStream is = null;
String result = "";
JSONArray jArray = null;
// http post
try {
HttpClient httpclient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
HttpResponse response = httpclient.execute(httpGet);
HttpEntity entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
return null;
}
// convert response to string
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();
result = sb.toString();
Log.e("log_tag", "JSON data" + result);
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
return null;
}
// try parse the string to a JSON object
try {
jArray = new JSONArray(result);
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
return null;
}
return jArray;
}
}
And this is my MainActivity where I call JSONparser to fetch some data that I need to display
JSONArray json = jParser.getJSONfromURL(temp);
if (json == null) {
return -1;
}
for (int i = 0; i < json.length(); i++) {
try {
JSONObject c = json.getJSONObject(i);
// Getting Array of Contacts
// Storing each json item in variable
asr_iq = c.getString("lMAsr");
sunrise_iq = c.getString("lMSunrise");
fajr_iq = c.getString("lMFajr");
isha_iq = c.getString("lMIsha");
dhuhr_iq = c.getString("lMDhuhr");
maghrib_iq = c.getString("lMMaghrib");
} catch (JSONException e) {
e.printStackTrace();
}
}

Load your asynctask on the UI thread.
If you cannot do any network related operation on the UI Thread Honeycomb and later. You will get a NetworkOnMainThread Exception.
new MyTask(url).execute();// can pass parameter to class constructor
// can also pass url to doInBackground.
Async task
class MyTask extends AsyncTask<Void,Void,Void>
{
String url;
public MyTask(String url)
{
this.url =url
}
#Override
protected Void doInBackground(Void... params) {
// all your network related operation
// invoked on the background thread
// all code from getJSONfromURL(param)
// do not update ui here
return null;
}
#Override
protected void onPostExecute(Void result) { // invoked on the ui thread
// TODO Auto-generated method stub
super.onPostExecute(result);
// dismiss progress dialog
// update ui here
}
#Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
// display progress dialog
}
#Override
protected void onProgressUpdate(Void... values) {
// TODO Auto-generated method stub
super.onProgressUpdate(values);
}
}
Detailed information # http://developer.android.com/reference/android/os/AsyncTask.html
Edit:
Use a Handler. Return result in doInBaCkground().
Example in onPostExecute()
Message msg=new Message();
msg.obj=result.getProperty(0).toString();
mHandler.sendMessage(msg);
In your activity onCreate()
Handler mHandler = new Handler() {
#Override public void handleMessage(Message msg) {
//ArrayList s=(ArrayList)msg.obj;
SoapObject s =(SoapObject) msg.obj;
tv.setText("Result = "+s.toString());
}
};
You can also use runonuithread to update ui from doInBackGround()
runOnUiThread(new Runnable() //run on ui thread
{
public void run()
{
_tv.setText("update from doinbackground");
}
});

Using Core Java,
Have your getJson execution logic in a Runnable/Callable(Java concurrency class), submit it via executors so that its an Asynch call.
Then with in your Runnable/Callable once json is retrived call the class which will have logic to display the json, this clas can be designed as a listener and you may publish an even after getting json response

NetworkOnMainThread exception android. fetching server response

I am getting the exception android.os.NetworkOnMainThreadException when I tried to use the following codes:
public class CheckServer extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
Runnable runn = null;
HttpTask.execute(runn);
}
private class HttpTask extends AsyncTask<String, String, String>
{
#Override
protected String doInBackground(String... params) {
// TODO Auto-generated method stub
HttpURLConnection urlConnection = null;
URL theURL = null;
try {
theURL = new URL("http://192.168.2.8/parkme/Client/clientquery.php?ticket=66t");
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
urlConnection = (HttpURLConnection) theURL.openConnection();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
String response = null;
try {
response = readInputStream(urlConnection.getInputStream());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return response;
}
private String readInputStream(InputStream is) {
// TODO Auto-generated method stub
String line = "";
StringBuilder total = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
try {
while ((line = rd.readLine()) != null) {
total.append(line);
}
} catch (Exception e) {
e.printStackTrace();
}
return total.toString();
}
#Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), result, Toast.LENGTH_LONG).show();
}
}}
If possible can someone tell me how to use it inside an Async Task and get the output? I tried but can't seem to get anywhere.

NetworkOnMainThread Exception occurs because you are running a network related operation on the main UI Thread.This is only thrown for applications targeting the Honeycomb SDK or higher
You should be using asynctask.
http://developer.android.com/reference/android/os/AsyncTask.html
In onCreate()
new TheTask().execute();
You can also pass parameters like url to the constructor of AsyncTask and use the same in doInBackground()
class TheTask extends AsyncTask<Void,Void,Void>
{
protected void onPreExecute()
{ super.onPreExecute();
//display progressdialog.
}
protected void doInBackground(Void ...params)//return result here
{
//http request. do not update ui here
return null;
}
protected void onPostExecute(Void result)//result of doInBackground is passed a parameter
{
super.onPostExecute(result);
//dismiss progressdialog.
//update ui using the result returned form doInbackground()
}
}
When an asynchronous task is executed, the task goes through 4 steps:
onPreExecute(), invoked on the UI thread before the task is executed. This step is normally used to setup the task, for instance by showing a progress bar in the user interface.
doInBackground(Params...), invoked on the background thread immediately after onPreExecute() finishes executing. This step is used to perform background computation that can take a long time. The parameters of the asynchronous task are passed to this step. The result of the computation must be returned by this step and will be passed back to the last step. This step can also use publishProgress(Progress...) to publish one or more units of progress. These values are published on the UI thread, in the onProgressUpdate(Progress...) step.
onProgressUpdate(Progress...), invoked on the UI thread after a call to publishProgress(Progress...). The timing of the execution is undefined. This method is used to display any form of progress in the user interface while the background computation is still executing. For instance, it can be used to animate a progress bar or show logs in a text field.
onPostExecute(Result), invoked on the UI thread after the background computation finishes. The result of the background computation is passed to this step as a parameter.

Ok, lets do it step by step ...
1) create private class extending AsyncTask
private class HttpUrlConnectionTask extends AsyncTask {
2) Override the doInBackground() method, this will do the heavy load
#Override
protected Object doInBackground(Object... params) {
// your HttpUrlConnection code goes here
return response;
3) Once the job is done and returns, the onPostExecute() method will be called. The result parameter contains the return value of doInBackground() - so response.
#Override
protected void onPostExecute(Object result) {
Within this method you can update your UI.
4) Finally lets have a look onto the HttpUrlConnection code
HttpURLConnection urlConnection = null;
URL theURL = new URL(url);
urlConnection = (HttpURLConnection) theURL.openConnection();
String response = readInputStream(urlConnection.getInputStream());
return response;
Hope this helps. Happy coding!

#Raghunandan comes with a really good explanation of how AsyncTask works
Here you go:
public static class InitializeTask extends MyAsyncTask<String, String, String> {
private Activity activity;
private ProgressDialog dialog;
public InitializeTask(Activity activity) {
this.activity = activity;
}
#Override
protected void onPostExecute(String result) {
Toast.makeText(activity, result, Toast.LENGTH_SHORT).show();
}
#Override
protected String doInBackground(String... params) {
HttpClient httpclient = new DefaultHttpClient();
HttpGet httpget = new HttpGet("http://192.168.2.8/localhost/parkme/Client/clientquery.php?ticket=");
try {
HttpResponse response = httpclient.execute(httpget);
if(response != null) {
String line = "";
InputStream inputstream = response.getEntity().getContent();
return convertStreamToString(inputstream);
} else {
return "Unable to complete your request";
}
} catch (ClientProtocolException e) {
return "Caught ClientProtocolException";
} catch (IOException e) {
return "Caught IOException";
}
}
private String convertStreamToString(InputStream is) {
String line = "";
StringBuilder total = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
try {
while ((line = rd.readLine()) != null) {
total.append(line);
}
} catch (Exception e) {
return "Stream Exception";
}
return total.toString();
}
}
A little side note, it is generally considered bad code to catch just Exception, since this will catch anything, and you are not accounting for what it is.
To use the AsyncTask in the Activity do this:
InitializeTask task = new InitializeTask(this)
task.execute()

Exactly as it says, network activity isn't allowed on the thread the activity ran in. Moving your code to an Asynctask is the way to do it properly. Though if you're just trying to get your concept working still you can do this...
//lazy workaround with newer than gingerbread
//normally UI thread can't get Internet.
if(Build.VERSION.SDK_INT >= 9){
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
}
And then the UI thread actually can. I wouldn't release anything like this however, I haven't even tried infact. It's just my lazy debugging move I use a lot.

Getting a hold of doInBackground(String... params)

In some way I do understand the Handler, but I'm not sure what to do with the params and how to let the code wait until the job is done in the background. I want the UI to be normally working and in the background I want to do an exchange rate calculation.
I have the following:
I call new getOnlineExchangeRate().execute(""); //Get Exchange Rate in BG
After that I want to have a result=amount*exchangerate, but the code is not waiting for the result.
Can somebody tell me how the calculation waits till we have an exchangerate. Do I have to send some params and how would that look?
.
.
.
.
.
public double getYahooExchangeRate(String ER){
double exchangerate=0;
try {
s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+ER+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");
//s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+val[from]+val[to]+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");
JSONObject jObj;
jObj = new JSONObject(s);
String exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");
exchangerate=Double.parseDouble(exResult);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
ALS.Toast(myContext.getString(R.string.conversionerror), false);
}
catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
ALS.Toast(myContext.getString(R.string.conversionerror), false);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
ALS.Toast(myContext.getString(R.string.conversionerror), false);
}
return exchangerate;
}
public String getJson(String url)throws ClientProtocolException, IOException {
StringBuilder build = new StringBuilder();
HttpClient client = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
HttpResponse response = client.execute(httpGet);
HttpEntity entity = response.getEntity();
InputStream content = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(content));
String con;
while ((con = reader.readLine()) != null) {
build.append(con);
}
return build.toString();
}
public class getOnlineExchangeRate extends AsyncTask<String, Void, String> {
#Override
protected void onPostExecute(String result) {
// execution of result of Long time consuming operation
ALS.Toast(myContext.getString(R.string.exchangeratesupdated), true);
}
#Override
protected String doInBackground(String... params) {
// TODO Auto-generated method stub
// perform long running operation operation
getYahooExchangeRate(USDEUR);
return null;
}

I think your problem is in this line:
#Override
protected String doInBackground(String... params) {
getYahooExchangeRate(USDEUR);
return null;
You want to return the result of getYahooExchangeRate and not null :)
So change this and the return-value should be a double. So change this to:
#Override
protected Double doInBackground(String... params){
return getYahooExchangeRate(USDEUR);
}
You also have to change your class header:
public class getOnlineExchangeRate extends AsyncTask<String, Void, Double> {
AsyncTask<Params, Progress, Result>
The generic part tells the AsyncTask which Informationstypes are handled.
The first is the type for the params of doInBackground(Params... )
The second is the type of the progress-Information
The last explains which type is returned by doInBackground(), so it changes the method-header from
protected Result doInBackground(Params... params){ };
to
protected double doInBackground(Params... params){};
To bring back the Result i would use and Observer oder Callback-Pattern.
Edit: changed double to Double, because primitives cannot be used for Generics.

the code is not waiting for the result. Can somebody tell me how the calculation waits till we have an exchangerate. Do I have to send some params and how would that look?
You could use AsyncTask#get() to force the code to wait, but this blocks the main thread until the AsyncTask completes which defies the purpose of using an asynchronous task.
It is best to design your Activity to proceed without the exchange rate, just like my mail app loads allowing me to compose messages and read old messages while the new messages are being fetched. When the asynchronous data loads then you can update your UI with the new information. (I believe this is what you are trying to do.)
To add on to user1885518 code, you should use your AsyncTask as a subclass in your Activity like this:
public class MainActivity extends Activity {
private class getOnlineExchangeRate extends AsyncTask<Void, Void, Double> {
#Override
protected Double doInBackground(Void... params) {
return getYahooExchangeRate(params[0]);
}
#Override
protected void onPostExecute(Double rate) {
// Do something with rate
}
}
...
}
Once you know which exchange rate you want, call:
new getOnlineExchangeRate().execute(USDEUR); //Get Exchange Rate in BG
Now when you have gotten the rate from online, the code calls onPostExecute() with your desired rate. Inside on onPostExceute() you can call whatever method you want in your ACtivity to calculate result=amount*exchangerate and display result wherever it is appropriate.

Android Asynctask: wait for entire computation without blocking UI thread

I have almost finished my project, only one thing remain to improve.
My app is a music quiz, that retrieves all the informations about author, song title, previewUrl ecc. from the Itunes Store using the apposite Search API.
When a user choose a genre to play with, I must say to the user to wait for 4-5 seconds because of the computation that fills the List containing all the informations.
I call the Asynctask that retrieve these informations like this:
JsonCanzoni recuperoCanzoni = new JsonCanzoni(arrayGenere,Canzone.this);
try {
recuperoCanzoni.execute().get();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
The class (extends Asynctask) that do these operation is the following:
class JsonCanzoni extends AsyncTask<Void, Void, Void>
{
List<String> canzoni = new ArrayList<String>(5);
ProgressDialog pDialog;
int[] arrayGenere;
Context context;
public JsonCanzoni(int[] arrayGenere,Context context)
{
this.arrayGenere = arrayGenere;
this.context = context;
}
#Override
protected void onPostExecute(Void result)
{
super.onPostExecute(result);
pDialog.dismiss();
}
#Override
protected void onPreExecute()
{
super.onPreExecute();
pDialog = new ProgressDialog(context);
pDialog.setMessage("Preparazione round...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected Void doInBackground(Void... params)
{
try
{
int randomLookupId = 0;
JSONObject obj;
JSONArray jsonArray;
for(int i = 0; i < 10; i++)
{
canzoni = new ArrayList<String>();
Log.d("GENERE", arrayGenere.toString());
obj = getJSONObject(scegliClassifica(arrayGenere));
jsonArray = obj.getJSONArray("resultIds");
Log.d("dimensione JsonArray", String.valueOf(jsonArray.length()));
try
{
randomLookupId = new Random().nextInt(jsonArray.length()-1);
}
catch(IllegalArgumentException errore)
{
new AlertDialog.Builder(context)
.setTitle("Connessione non attiva!")
.setMessage("Connessione di rete debole, uscita dal programma!");
}
Log.d("randomLookupID", String.valueOf(randomLookupId));
JSONObject finalObj = getJSONObject("http://itunes.apple.com/lookup?id="+jsonArray.getString(randomLookupId));
Log.d("URL","http://itunes.apple.com/lookup?id="+jsonArray.getString(randomLookupId));
while(finalObj.getJSONArray("results").length() == 0)
{
Log.d("Array VUOTO!!","Non è possibile!!!!");
randomLookupId = new Random().nextInt(jsonArray.length()-1);
Log.d("randomID rigenerato", String.valueOf(randomLookupId));
finalObj = getJSONObject("http://itunes.apple.com/lookup?id="+jsonArray.getString(randomLookupId));
Log.d("URL Rigenerato","http://itunes.apple.com/lookup?id="+jsonArray.getString(randomLookupId));
}
JSONArray finalJsonArray = finalObj.getJSONArray("results");
JSONObject returnObj = finalJsonArray.getJSONObject(0);
Log.d("returnObj.length",String.valueOf(returnObj.length()));
canzoni.add(returnObj.getString("previewUrl"));
canzoni.add(returnObj.getString("artistName"));
canzoni.add(returnObj.getString("trackName"));
canzoni.add(returnObj.getString("artistViewUrl"));
canzoni.add(returnObj.getString("artworkUrl100"));
// GTTapp app=(GTTapp) ((Activity)context).getApplication();
// app.dieciCanzoni;
Canzone.dieciCanzoni.add(i, new ArrayList<String>(canzoni));
}
}
catch (JSONException ignored)
{
ignored.getCause();
}
catch (MalformedURLException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
private String scegliClassifica(int[] arrayGenere)
{
int randomArrayPosition = new Random().nextInt(arrayGenere.length);
return "http://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/charts?cc=us&g="+arrayGenere[randomArrayPosition]+"&name=Songs&limit=200";
}
JSONObject getJSONObject(String url) throws IOException, MalformedURLException, JSONException
{
HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
InputStream in = conn.getInputStream();
try
{
StringBuilder sb = new StringBuilder();
BufferedReader r = new BufferedReader(new InputStreamReader(new DoneHandlerInputStream(in)));
for (String line = r.readLine(); line != null; line = r.readLine())
{
sb.append(line);
}
return new JSONObject(sb.toString());
}
finally
{
in.close();
}
}
}
THE PROBLEM: Using the .get() method make the app waiting for the entire computation of the AsyncTask, but it block the UI thread too!! So the user will remain with a black screen for 5 secs or more, and that's not a good thing!
If I don't use the .get() method, I receive an IndexOutOfBounds Exception, because I begin to play the music stream but the list is has not been filled yet.
Can you suggest me a workarund for this situation?
Thank you!

remove .get() it will block the UI till completion of the task.
Start any task like (playing video) which is dependent on AsycTask in
#Override
protected void onPostExecute(Void result)
{
super.onPostExecute(result);
pDialog.dismiss();
//You can start music stream here
}

The get() call is blocking. From the docs:
Waits if necessary for the computation to complete, and then retrieves its result.
What you should do is wait asynchronously the computation to finish before you start to play the music.
If you do not want to expose the asynctask outside your class, you can set a callback into your JSonCanzoni class to be called into the onPostExecute method of the asynctask.
Something like
public interface CanzoniDownloadedInterface {
public void onCanzoniDownloaded();
}
public JsonCanzoni(int[] arrayGenere, CanzoniDownloadedInterface callback, Context context){
this.arrayGenere = arrayGenere;
this.context = context;
this.callback = callback;
}
and in your onPostExecute():
#Override
protected void onPostExecute(Void result)
{
super.onPostExecute(result);
this.callback.onCanzoniDownloaded();
pDialog.dismiss();
}
If you let your activity implement the interface, you can pass it to your class.
The onCanzoniDownloaded() implementation is where you need to start playing.

Finally I solved my problem, some advices were good and helped me a lot!
I simply moved the startActivity instruction to onPostExecute of JsonCanzoni AsyncTask, and changed some code to adapt to the new version and it's all right! ;)