I have an Activity (RecipiesActivity) that is opened by clicking on the "Next" button of the Main Activitiy of my application.
In the RecipiesActivity onCreate, I want to call a webservice in an AsyncTask. For now, since I have not implemented the webservice yet, I am just calling a webservice provided by bitly (but this is irrelevant to my problem).
The problem is that although the webservice gets called and no exception is thrown, a result is return from the doInBackground, but my onPostExecute is not called. I have done some research and I have found the possible reasons as listed below - but none seem to be my case:
onPostExecute parameters do not match the AsyncTask parameters - in my case they match
A bug in android that does not allow the AsyncTask to be executed in the UI thread. It is supposadely overcomes by using Class.forName("android.os.AsyncTask") - I tried this and did not make any difference
AsyncTask is not started from the UI thread - in my case I believe it is
doInBackground does not return - in my case it does, I have stepped through it with the debugger
#Override is not used before onPostExecute - in my case I am using #Override
The code is below:
public class RecipiesActivity extends Activity {
private TextView tv;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_recipies);
tv = (TextView) findViewById(R.id.Response);
//Start the WS call in an AsyncTask
new CallWS().doInBackground("https://api-ssl.bitly.com/v3/shorten?login=maskedLogin&apiKey=maskedKey&longUrl=http%3A%2F%2Fgoogle.com%2F");
}
private class CallWS extends AsyncTask<String, Integer, String>
{
#Override
protected String doInBackground(String... params) {
String result = null;
HttpClient httpClient = new DefaultHttpClient();
HttpContext localContext = new BasicHttpContext();
HttpGet get_request = new HttpGet(params[0]);
try
{
HttpResponse httpResponse = httpClient.execute(get_request, localContext);
//int responseCode = httpResponse.getStatusLine().getStatusCode();
HttpEntity entity = httpResponse.getEntity();
if (entity != null)
{
InputStream istream = entity.getContent();
BufferedReader br = new BufferedReader(new InputStreamReader(istream));
try
{
result = br.readLine();
}
catch (Exception e)
{
//TODO Handle the IOException that the readline may throw
}
finally
{
istream.close();
}
}
}catch (Exception e)
{
//TODO Handle the IOException and the ClientProtocolException that the
// httpClient.execute can throw
}
finally
{
httpClient.getConnectionManager().shutdown();
}
return result;
}
#Override
protected void onPostExecute(String result)
{
if (result == null)
{
tv.setText("The result is NULL");
}
else
{
tv.setText(result);
}
}
}
}
Your help is appreceiated,
thanks
Instead of doInBackground(), simply call the execute() method of the AsyncTask. Calling doInBackground() does what it says on the tin: calls doInBackground() (in the same thread) and returns. It won't call onPostExecute() for you. execute() will start a background thread, call doInBackground() on the background thread, then post the result of doInBackground() to onPostExecute() on the UI thread.
Try changing this line
new CallWS().doInBackground("https://api-ssl.bitly.com/v3/shorten?login=maskedLogin&apiKey=maskedKey&longUrl=http%3A%2F%2Fgoogle.com%2F");
to
new CallWS().execute("https://api-ssl.bitly.com/v3/shorten?login=maskedLogin&apiKey=maskedKey&longUrl=http%3A%2F%2Fgoogle.com%2F");
Make sure your onPostExecute function has #Override
Related
i want to get the value returns by asynctask after it's been completed. this is my code :
class asyncGet extends AsyncTask<Void, String, String> {
Boolean goterror = false;
#Override
protected String doInBackground(Void... params) {
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet(url);
HttpResponse response;
try {
request.setHeader("Cache-Control", "no-cache");
request.setHeader("Cache-Control", "no-store");
response = client.execute(request);
response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
response.setHeader("Pragma", "no-cache");
InputStream in = response.getEntity().getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
StringBuilder str = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
str.append(line);
}
in.close();
return str.toString();
} catch (Exception e) {
goterror = true;
}
return null;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
if (pDialog != null && pDialog.isShowing())
pDialog.dismiss();
if (result != null && goterror == false) {
}
}
The async is in another class , I want to show the result when it's done .
How can I return the result from the async ?
thanks
if you want to keep it asynchronous then it is already implemented in your code,
use onPostExecute method, "result" contains the returned data.
Or if you want it to return data synchronously then use the extended asynctask like below:
try {
String result = new asyncGet().execute().get();
} catch (InterruptedException e) {
e.printStackTrace(); //handle it the way you like
} catch (ExecutionException e) {
e.printStackTrace();//handle it the way you like
}
You can create an interface, as follows:
public interface OnStringListener {
void onStringCompleted(String s);
void onStringError(String error);
}
and you will have to create the constructor of your AsyncTask with OnStringListener as parameter:
class asyncGet extends AsyncTask<Void, String, String> {
Boolean goterror = false;
private final OnStringListener mListener;
public asyncGet(OnStringListener listener) {
mListener = listener;
}
//The rest of your code
And in your onPostExecute method you can return the String sending it by the method onStringCompleted:
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
if (pDialog != null && pDialog.isShowing())
pDialog.dismiss();
if (result != null && goterror == false) {
}
if (mListener != null) {
mListener.onStringCompleted(result);
}
}
Of course, your methods onStringCompleted and onStringError have to be created in the Activity that you want to get the result of your AsyncTask. From there, you will be able to use your result in your other class.
I expect it will be helpful to you!
AsyncTask enables proper and easy use of the UI thread. This class allows to perform background operations and publish results on the UI thread without having to manipulate threads and/or handlers.
AsyncTask must be subclassed to be used. The subclass will override at least one method (doInBackground(Params...)), and most often will override a second one (onPostExecute(Result).)
So the philosophy is you override doInBackground and when the doInBackground finishes its task it passes the result to onPostExecute which result is available in your main thread.
Read the Full usage here
and if you still want synchronous execution call get() as explained by #meghraj27
You can implement an interface to an Activity or class where you want the result of the AsynTask and trigger that interface from the AsynTask.
You can refer this post
How to handle return value from AsyncTask
I'm trying to see how works an Asynctask class in android. In particular i want reveal in real time the status of the class for see when it is running and when it has finished. For do this, i have created a class that extend the main activity and another class that is the asynctaks class.
This is my main class:
public class PhotoManagement extends Activity{
private String numberOfSelectedPhotos;
private Bitmap currentImage;
private String initConfiguration = "http://www.something.com";
private String response;
private ArrayList<String> formatPhotoList = new ArrayList<String>(); //create a list that will contains the available format of the photos downloaded from the server
private ArrayList<String> pricePhotoList = new ArrayList<String>(); //create a list that will contains the available price for each format of the photos
DownloadWebPageTask webPage = new DownloadWebPageTask();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
protected void onResume(){
super.onResume();
webPage.execute(initConfiguration);
if(webPage.getStatus() == AsyncTask.Status.PENDING){
Log.i("STATUS","PENDING");
}
if(webPage.getStatus() == AsyncTask.Status.RUNNING){
Log.i("","RUNNING");
}
if(webPage.getStatus() == AsyncTask.Status.FINISHED){
Log.i("","FINISHED");
}
}
}
As you can see i want only see the passages of the status with a simple log.
And here there is the asynctask class.
private class DownloadWebPageTask extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... urls) {
for (String url : urls) {
DefaultHttpClient client = new DefaultHttpClient(); //create a new http client
HttpGet httpGet = new HttpGet(url); //create a new http request passing a valid url
try {
HttpResponse execute = client.execute(httpGet); //try to execute the http get request
InputStream content = execute.getEntity().getContent(); //prepare the input stream to read the bytes of the request
BufferedReader buffer = new BufferedReader(
new InputStreamReader(content));
String s = "";
while ((s = buffer.readLine()) != null) {
response += s; //until is present a line to read, the response variable store the value of the lines
}
} catch (Exception e) {
Log.i("MyApp", "Download Exception : " + e.toString()); //Print the error if something goes wrong
}
}
return response; //return the response
}
#Override
protected void onPostExecute(String result) {
result = doInBackground(initConfiguration); //take the result from the DownloadWebPageTask class
result = result.replace("null", "");
Log.i("RESULT",""+result);
//find the price and format value from the result using XmlPullParser
try {
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
factory.setNamespaceAware(true);
XmlPullParser xpp = factory.newPullParser();
xpp.setInput( new StringReader ( result ) );
int attributeNumber = xpp.getAttributeCount();
int eventType = xpp.getEventType();
String currentTag = null;
while(eventType != XmlPullParser.END_DOCUMENT){
if(eventType == XmlPullParser.START_TAG) {
currentTag = xpp.getName();
if (currentTag.equals("product")){
xpp.getAttributeValue(null, "name");
formatPhotoList.add(xpp.getAttributeValue(null, "name"));
Log.i("FORMAT PHOTO",""+xpp.getAttributeValue(null, "name"));
}
}
eventType = xpp.next();
}
} catch (XmlPullParserException e) {
e.printStackTrace();
Log.i("","ERROR XML PULL PARSER");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
Log.i("","ERROR IOEXCEPTION");
}
}
}
}
As you can see i have implemented also the method onPostExecute that should be called when the asynctask method has finished to execute the instructions right?
So at this point i don't understand why my log RUNNING and my log FINISHED never appear on the log cat.
What i'm doing wrong?
I'm tried to follow this topic Android, AsyncTask, check status? but in my case it isn't working.
Thanks
Problem :
You are creating object like
DownloadWebPageTask webPage = new DownloadWebPageTask();
But you are calling asynctask on different object,
new DownloadWebPageTask().execute(initConfiguration);
Solution :
It should be like
webPage.execute(initConfiguration);
#Override
protected void onResume(){
super.onResume();
new DownloadWebPageTask().execute(initConfiguration);
here do like this
#Override
protected void onResume(){
super.onResume();
webPage.execute(initConfiguration);
You didn't implement webPage.execute(), add it
Most probably the task hasn't finished or even started yet. As you probably know the AsyncTask is doing it's (background) work on a different thread, so your onResume is running in parallel with it. You can either use the task's get() method to wait for it to finish and get the result of the doInBackground() method and then query for it's status or notify your activity from the task's onPostExecute() method to let it know (and log) that it has finished. I don't recommend you the first option because it will actually block the UI thread and will make your usage of AsyncTask pointless.
i wrote those threads:
How to manage multiple Async Tasks efficiently in Android
Running multiple AsyncTasks at the same time -- not possible?
but didnt find answer for my question, maybe someone can help..
I have android app which makes Login POST and getting json response,
if the Json is OK i need to POST another data to get another response.
i have extends Async Class which doing the post to the URL:
public class AsyncHttpPost extends AsyncTask<String, String, String> {
private HashMap<String, String> mData = null;
public AsyncHttpPost(HashMap<String, String> data) {
mData = data;
}
#Override
protected String doInBackground(String... params) {
byte[] result = null;
String str = "";
HttpClient client = new DefaultHttpClient();
HttpPost post = new HttpPost(params[0]);// in this case, params[0] is URL
try {
ArrayList<NameValuePair> nameValuePair = new ArrayList<NameValuePair>();
Iterator<String> it = mData.keySet().iterator();
while (it.hasNext()) {
String key = it.next();
nameValuePair.add(new BasicNameValuePair(key, mData.get(key)));
}
post.setEntity(new UrlEncodedFormEntity(nameValuePair, "UTF-8"));
HttpResponse response = client.execute(post);
StatusLine statusLine = response.getStatusLine();
if(statusLine.getStatusCode() == HttpURLConnection.HTTP_OK){
result = EntityUtils.toByteArray(response.getEntity());
str = new String(result, "UTF-8");
}
}
catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
catch (Exception e) {
return null;
}
return str;
}
#Override
protected void onPostExecute(String result) {
try {
JSONArray Loginjson = new JSONArray(result);
strStt = Loginjson.getJSONObject(0).getJSONObject("fields").getString("status");
if (strStt.equals("ERR")) {
ErrorMsg("Authentication failed");
} else if (strStt.equals("OK")) {
ErrorMsg("Login OK!!!");
ClientPage();
} else {
ErrorMsg("Connection Error");
}
} catch (JSONException e) {
ErrorMsg("Connection Error");
}
}
}
Now - i need to get another POST if the status is Error. do i need to make another Async class? with the same all procedures ? the issue is only the onPostExecute part is different.. actually the "doInBackground" will be always the same..
any idea how can i easily do multiple posts in the same activity?
Firstly, since your doInBackground() code will always stay the same, I recommend you move it into a general utility class.
Beyond that, you can go one of two ways:
Create a new AsyncTask for each type of request that can call your utility class, and have its own onPostExecute()
Create one AsyncTask that has a flag in it, which can be checked in the onPostExecute() method to see what code needs to be executed there. You will have to pass the flag in in the constructor or as a parameter in execute.
You can use a parameter at AsyncHttpPost constructor/execute or global variable to indicate if it is first or second POST (by other words - a flag). Then just create and execute another instance of AsyncHttpPost in onPostExecute (only if parameter/variable is set as "first POST").
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.
I have to download huge amount of data from server. It is taking minimum 10 seconds to download. Here is my code to download using asyntask class. And I want to cancel the downloading operation unconditionally if the user clicks on home button while downloading operation is going on. The problem is... I'am executing cancel() method but it is not cancelling the downloading operation. I'am seeing that operation is running in background in logcat view even i came out of application. I just want to stop the execution of doInBackground() method. Please guide/help me.
on click of download button :
dwnldTask = new DownloadTask ();
dwnldTask.execute(SERVER_URL);
And here is Asynctask class :
class DownloadTask extends AsyncTask<String, Void, Object>{
private Object response = null;
#Override
protected void onPreExecute() {
super.onPreExecute();
displaying progress dialog on UI
}
#Override
protected Object doInBackground(String... params) {
try{
DataConnection dc = new DataConnection();
this.response = dc.connectToServer(params[0]);
if(isCancelled()){
return null;
}
}catch (Exception e) {
if(isCancelled()){
return null;
}
e.printStackTrace();
showToastMSG(e.getMessage());
}
return this.response ;
}
#Override
protected void onPostExecute(Object response) {
super.onPostExecute(response);
if(response != null ){
successfully downloaded... go to next activity
}
cancel progress dialog here
}
}
Inside onPause()..
#Override
protected void onPause() {
super.onPause();
if(dwnldTask != null && dwnldTask.getStatus() == AsyncTask.Status.RUNNING){
dwnldTask.cancel(true);
}
cancel the progress dialog if it is showing
}
Here is the method located in another class named DataConnection...
public Object connectToServer(String url) throws Exception{
HttpGet request = new HttpGet(url);
request.addHeader("accept","application/json");
HttpResponse response = httpClient.execute(request);
HttpEntity httpEntity = response.getEntity();
InputStream responseInputStream = httpEntity.getContent();
return myUtilObject.convertInputStreamToString(responseInputStream);
}
I agree with Ran - you didn't write the code of:
myUtilObject.convertInputStreamToString
but im guessing you loop there over the inputstream with a buffer you predefined its size (maybe with BufferedReader?) - in this loop you should check the stop condition of your async thread - isCancelled() is a good example.
The loop should stop if the thread is canceled, i.e.:
String line = "";
StringBuilder total = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is), 1024);
while ((line = rd.readLine()) != null && !isCancelled())
{
total.append(line);
}
You are checking the isCancelled() method after you perform the download, so there's no reason it would get cancelled in the middle.
Usually you do something like this:
while (!isCancelled()) {
// Download next buffer..
}
In this case, the loop will stop once a cancel request has been made.