I am running remote audio-file-fetching and audio file playback operations in a background thread using AsyncTask. A Cancellable progress bar is shown for the time the fetch operation runs.
I want to cancel/abort the AsyncTask run when the user cancels (decides against) the operation. What is the ideal way to handle such a case?
Just discovered that AlertDialogs's boolean cancel(...); I've been using everywhere actually does nothing. Great.
So...
public class MyTask extends AsyncTask<Void, Void, Void> {
private volatile boolean running = true;
private final ProgressDialog progressDialog;
public MyTask(Context ctx) {
progressDialog = gimmeOne(ctx);
progressDialog.setCancelable(true);
progressDialog.setOnCancelListener(new OnCancelListener() {
#Override
public void onCancel(DialogInterface dialog) {
// actually could set running = false; right here, but I'll
// stick to contract.
cancel(true);
}
});
}
#Override
protected void onPreExecute() {
progressDialog.show();
}
#Override
protected void onCancelled() {
running = false;
}
#Override
protected Void doInBackground(Void... params) {
while (running) {
// does the hard work
}
return null;
}
// ...
}
If you're doing computations:
You have to check isCancelled() periodically.
If you're doing a HTTP request:
Save the instance of your HttpGet or HttpPost somewhere (eg. a public field).
After calling cancel, call request.abort(). This will cause IOException be thrown inside your doInBackground.
In my case, I had a connector class which I used in various AsyncTasks. To keep it simple, I added a new abortAllRequests method to that class and called this method directly after calling cancel.
The thing is that AsyncTask.cancel() call only calls the onCancel function in your task. This is where you want to handle the cancel request.
Here is a small task I use to trigger an update method
private class UpdateTask extends AsyncTask<Void, Void, Void> {
private boolean running = true;
#Override
protected void onCancelled() {
running = false;
}
#Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
onUpdate();
}
#Override
protected Void doInBackground(Void... params) {
while(running) {
publishProgress();
}
return null;
}
}
Simple: don't use an AsyncTask. AsyncTask is designed for short operations that end quickly (tens of seconds) and therefore do not need to be canceled. "Audio file playback" does not qualify. You don't even need a background thread for ordinary audio file playback.
The only way to do it is by checking the value of the isCancelled() method and stopping playback when it returns true.
This is how I write my AsyncTask
the key point is add Thread.sleep(1);
#Override protected Integer doInBackground(String... params) {
Log.d(TAG, PRE + "url:" + params[0]);
Log.d(TAG, PRE + "file name:" + params[1]);
downloadPath = params[1];
int returnCode = SUCCESS;
FileOutputStream fos = null;
try {
URL url = new URL(params[0]);
File file = new File(params[1]);
fos = new FileOutputStream(file);
long startTime = System.currentTimeMillis();
URLConnection ucon = url.openConnection();
InputStream is = ucon.getInputStream();
BufferedInputStream bis = new BufferedInputStream(is);
byte[] data = new byte[10240];
int nFinishSize = 0;
while( bis.read(data, 0, 10240) != -1){
fos.write(data, 0, 10240);
nFinishSize += 10240;
**Thread.sleep( 1 ); // this make cancel method work**
this.publishProgress(nFinishSize);
}
data = null;
Log.d(TAG, "download ready in"
+ ((System.currentTimeMillis() - startTime) / 1000)
+ " sec");
} catch (IOException e) {
Log.d(TAG, PRE + "Error: " + e);
returnCode = FAIL;
} catch (Exception e){
e.printStackTrace();
} finally{
try {
if(fos != null)
fos.close();
} catch (IOException e) {
Log.d(TAG, PRE + "Error: " + e);
e.printStackTrace();
}
}
return returnCode;
}
Our global AsyncTask class variable
LongOperation LongOperationOdeme = new LongOperation();
And KEYCODE_BACK action which interrupt AsyncTask
#Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
LongOperationOdeme.cancel(true);
}
return super.onKeyDown(keyCode, event);
}
It works for me.
I don't like to force interrupt my async tasks with cancel(true) unnecessarily because they may have resources to be freed, such as closing sockets or file streams, writing data to the local database etc. On the other hand, I have faced situations in which the async task refuses to finish itself part of the time, for example sometimes when the main activity is being closed and I request the async task to finish from inside the activity's onPause() method. So it's not a matter of simply calling running = false. I have to go for a mixed solution: both call running = false, then giving the async task a few milliseconds to finish, and then call either cancel(false) or cancel(true).
if (backgroundTask != null) {
backgroundTask.requestTermination();
try {
Thread.sleep((int)(0.5 * 1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
if (backgroundTask.getStatus() != AsyncTask.Status.FINISHED) {
backgroundTask.cancel(false);
}
backgroundTask = null;
}
As a side result, after doInBackground() finishes, sometimes the onCancelled() method is called, and sometimes onPostExecute(). But at least the async task termination is guaranteed.
With reference to Yanchenko's answer on 29 April '10:
Using a 'while(running)' approach is neat when your code under 'doInBackground' has to be executed multiple times during every execution of the AsyncTask. If your code under 'doInBackground' has to be executed only once per execution of the AsyncTask, wrapping all your code under 'doInBackground' in a 'while(running)' loop will not stop the background code (background thread) from running when the AsyncTask itself is cancelled, because the 'while(running)' condition will only be evaluated once all the code inside the while loop has been executed at least once. You should thus either
(a.) break up your code under 'doInBackground' into multiple 'while(running)' blocks or
(b.) perform numerous 'isCancelled' checks throughout your 'doInBackground' code, as explained under "Cancelling a task" at https://developer.android.com/reference/android/os/AsyncTask.html.
For option (a.) one can thus modify Yanchenko's answer as follows:
public class MyTask extends AsyncTask<Void, Void, Void> {
private volatile boolean running = true;
//...
#Override
protected void onCancelled() {
running = false;
}
#Override
protected Void doInBackground(Void... params) {
// does the hard work
while (running) {
// part 1 of the hard work
}
while (running) {
// part 2 of the hard work
}
// ...
while (running) {
// part x of the hard work
}
return null;
}
// ...
For option (b.) your code in 'doInBackground' will look something like this:
public class MyTask extends AsyncTask<Void, Void, Void> {
//...
#Override
protected Void doInBackground(Void... params) {
// part 1 of the hard work
// ...
if (isCancelled()) {return null;}
// part 2 of the hard work
// ...
if (isCancelled()) {return null;}
// ...
// part x of the hard work
// ...
if (isCancelled()) {return null;}
}
// ...
Related
I am making an app which sends update to web server when a songs starts playing...I do the the web server update through asynctask however some times some information gets skipped and some infos are sent repeatedly. In some case asyntask remain in running state making it not executing after that. Main thread works good.
I declared the instance like this in MainActivity
private static AsyncTask<Void, Void, Void> mTask = null;
code for Asynctask is
private class SendingData extends AsyncTask<Void,Void,Void>{
#Override
protected void onPreExecute(){
//some task
}
protected void onPostExecute(Void params){
Log.d("Tesing","After Post");
super.onPostExecute(params);
}
#Override
protected Void doInBackground(Void... arg0) {
sendPost();
return null;
}
}
My call to asynctask when a new song changes in main thread. This is a repetitive call
if(mTask.getStatus() == AsyncTask.Status.FINISHED){
// My AsyncTask is done and onPostExecute was called
Log.d("AsyncTask Status","Finished");
mTask = new SendingData();
mTask.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
}else if(mTask.getStatus() == AsyncTask.Status.PENDING){
Log.d("AsyncTask Status","Pending");
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
mTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
You declared your AsyncTask as static variable. This means that your references will get mixed up, i.e. when you start a new AsyncTask, you will overwrite the previous reference with a new one.
My app sends data to the server. It generally works fine until the user is in a bad signal area. If the user is in a good signal area the the following code works fine and the data is sent.
String[] params = new String[]{compID, tagId, tagClientId, carerID,
formattedTagScanTime, formattedNowTime, statusForWbService, getDeviceName(), tagLatitude, tagLongitude};
AsyncPostData apd = new AsyncPostData();
apd.execute(params);
.
private class AsyncPostData extends AsyncTask<String, Void, String> {
ProgressDialog progressDialog;
String dateTimeScanned;
#Override
protected void onPreExecute()
{
// progressDialog= ProgressDialog.show(NfcscannerActivity.this,
// "Connecting to Server"," Posting data...", true);
int buildVersionSdk = Build.VERSION.SDK_INT;
int buildVersionCodes = Build.VERSION_CODES.GINGERBREAD;
Log.e(TAG, "buildVersionSdk = " + buildVersionSdk
+ "buildVersionCodes = " + buildVersionCodes);
int themeVersion;
if (Build.VERSION.SDK_INT > Build.VERSION_CODES.GINGERBREAD) {
themeVersion = 2;
}else{
themeVersion = 1;
}
progressDialog = new ProgressDialog(NfcscannerActivity.this, themeVersion);
progressDialog.setTitle("Connecting to Server");
progressDialog.setMessage(" Sending data to server...");
progressDialog.setIndeterminate(true);
try{
progressDialog.show();
}catch(Exception e){
//ignore
}
};
#Override
protected String doInBackground(String... params) {
Log.e(TAG, "carerid in doinbackground = " + params[3] + " dateTimeScanned in AsyncPost for the duplecate TX = " + params[4]);
dateTimeScanned = params[4];
return nfcscannerapplication.loginWebservice.postData(params[0], params[1], params[2], params[3], params[4],
params[5], params[6], params[7] + getVersionName(), params[8], params[9]);
}
#Override
protected void onPostExecute(String result)
{
super.onPostExecute(result);
try{
progressDialog.dismiss();
}catch(Exception e){
//ignore
}
if( result != null && result.trim().equalsIgnoreCase("OK") ){
Log.e(TAG, "about to update DB with servertime");
DateTime sentToServerAt = new DateTime();
nfcscannerapplication.loginValidate.updateTransactionWithServerTime(sentToServerAt,null);
nfcscannerapplication.loginValidate.insertIntoDuplicateTransactions(dateTimeScanned);
tagId = null;
tagType = null;
tagClientId = null;
//called to refresh the unsent transactions textview
onResume();
}else if(result != null && result.trim().equalsIgnoreCase("Error: TX duplicated")){
Log.e(TAG, "response from server is Duplicate Transaction ");
//NB. the following time may not correspond exactly with the time on the server
//because this TX has already been processed but the 'OK' never reached the phone,
//so we are just going to update the phone's DB with the DupTX time so the phone doesn't keep
//sending it.
DateTime sentToServerTimeWhenDupTX = new DateTime();
nfcscannerapplication.loginValidate.updateTransactionWithServerTime(sentToServerTimeWhenDupTX,null);
tagId = null;
tagType = null;
tagClientId = null;
}else{
Toast.makeText(NfcscannerActivity.this,
"No phone signal or server problem",
Toast.LENGTH_LONG).show();
}
}
}//end of AsyncPostData
.
The app in bad signal areas tends to show the progress bar for a few minutes before showing a black screen for a while rendering the app unusable.
I thought a way around this would be to do the following.
String[] params = new String[]{compID, tagId, tagClientId, carerID,
formattedTagScanTime, formattedNowTime, statusForWbService, getDeviceName(), tagLatitude, tagLongitude};
AsyncPostData apd = new AsyncPostData();
try {
apd.execute(params).get(10, TimeUnit.SECONDS);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (TimeoutException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
This will cause the AsyncTask to cancel after 10 seconds, but as it is executing there is a black screen until the data is sent followed by the progressbar for a few millisecs.
Is there a way to show the progressbar whilst executing an AsyncTask.get()?
thanks in advance. matt.
Also are there any ideas why the black screen comes when the user is in bad signal area and therefor no response from the server. This senario seems to cause the app alot of problems where it's behavior is unusual afterwards like sending extra transactions at a later date.
[edit1]
public class SignalService extends Service{
NfcScannerApplication nfcScannerApplication;
TelephonyManager SignalManager;
PhoneStateListener signalListener;
private static final int LISTEN_NONE = 0;
private static final String TAG = SignalService.class.getSimpleName();
#Override
public void onCreate() {
super.onCreate();
// TODO Auto-generated method stub
Log.e(TAG, "SignalService created");
nfcScannerApplication = (NfcScannerApplication) getApplication();
signalListener = new PhoneStateListener() {
public void onSignalStrengthChanged(int asu) {
//Log.e("onSignalStrengthChanged: " , "Signal strength = "+ asu);
nfcScannerApplication.setSignalStrength(asu);
}
};
}
#Override
public void onDestroy() {
super.onDestroy();
// TODO Auto-generated method stub
Log.e(TAG, "SignalService destroyed");
SignalManager.listen(signalListener, LISTEN_NONE);
}
#Override
public void onStart(Intent intent, int startId) {
super.onStart(intent, startId);
// TODO Auto-generated method stub
Log.e(TAG, "SignalService in onStart");
SignalManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
SignalManager.listen(signalListener, PhoneStateListener.LISTEN_SIGNAL_STRENGTH);
}
#Override
public IBinder onBind(Intent intent) {
// TODO Auto-generated method stub
return null;
}
}
You do not need a timer at all to do what you're attempting (for some reason I thought you were trying to loop the AsyncTask based on your comments above which resulted in mine.). If I understand correctly you're issue is with the loss of service. You have an AsyncTask that you start which may or may not finish depending on certain conditions. Your approach was to use get and cancle the task after a fixed time in the event that it did not finish executing before then - the assumption being if the task didn't finish within the 10 second cut off, service was lost.
A better way to approach this problem is to use a boolean flag that indcates whether network connectivity is available and then stop the task from executing if service is lost. Here is an example I took from this post (I apologize for the formatting I'm on a crappy computer with - of all things - IE8 - so I can't see what the code looks like).
public class MyTask extends AsyncTask<Void, Void, Void> {
private volatile boolean running = true;
private final ProgressDialog progressDialog;
public MyTask(Context ctx) {
progressDialog = gimmeOne(ctx);
progressDialog.setCancelable(true);
progressDialog.setOnCancelListener(new OnCancelListener() {
#Override
public void onCancel(DialogInterface dialog) {
// actually could set running = false; right here, but I'll
// stick to contract.
cancel(true);
}
});
}
#Override
protected void onPreExecute() {
progressDialog.show();
}
#Override
protected void onCancelled() {
running = false;
}
#Override
protected Void doInBackground(Void... params) {
while (running) {
// does the hard work
}
return null;
}
// ...
}
This example uses a progress dialog that allows the user to cancle the task by pressing a button. You're not going to do that but rather you're going to check for network connectivty and set the running boolean based on whether your task is connected to the internet. If connection is lost - running will bet set to false which will trip the while loop and stop the task.
As for the work after the task complete. You should NEVER use get. Either (1) put everything that needs to be done after the doInBackgroundCompletes in onPostExecute (assuming its not too much) or (2) if you need to get the data back to the starting activity use an interface. You can add an interface by either adding as an argument to your tasks constructor or using a seperate method that sets the interface up. For example
public void setInterface(OnTaskComplete listener){
this.listener = listener;
}
Where OnTaskComplete listener is declared as an instance variable in your AsyncTask. Note the approach I am describing requires using a seperate AsyncTask class. Your's is private right now which means you need to change your project a little.
UPDATE
To check connectivity I would use something like this.
public boolean isNetworkOnline() {
boolean status=false;
try{
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getNetworkInfo(0);
if (netInfo != null && netInfo.getState()==NetworkInfo.State.CONNECTED) {
status= true;
}else {
netInfo = cm.getNetworkInfo(1);
if(netInfo!=null && netInfo.getState()==NetworkInfo.State.CONNECTED)
status= true;
}
}catch(Exception e){
e.printStackTrace();
return false;
}
return status;
}
You can check to see if there is an actual network connection over which your app can connect to ther server. This method doesn't have to be public and can be part of you're AsyncTask class. Personally, I use something similar to this in a network manager class that I use to check various network statistics (one of which is can I connect to the internet).
You would check connectivity before you started executing the loop in your doInBackground method and then you could periodicly update throughout the course of that method. If netowkr is available the task will continue. If not it will stop.
Calling the AsyncTask built in cancle method is not sufficient becuase it only prevent onPostExecute from running. It does not actually stop the code from execting.
In my application, a client is connected to server. It waits until the connection to the server occurs. During that time the application is not responding. How can i solve this problem. Tried code snippet shows below
public Connection(){
client.SetParent(this);
this.context = g.getContext();
bConnected = false;
mNetworkRunner = new Runnable() {
public void run() {
try {
Log.e("", "mNetworkRunner...");
if( SendKeepAlive()){
Main.conStatus(1);
Log.e("", "SendKeepAlive...");
}
else {
Main.conStatus(0);
Log.e("", "No connection...");
g.log("Connection to server is lost... Trying to Connect...");
while(true){
Log.e("", "In while loop...");
if(!Connect()){
g.log("Trying...");
Log.e("", "In Connect no connect...");
Thread.sleep(2000);
}
else {
g.log("Connected");
break;
}
}
Main.conStatus(1);
}
mNetworkHandler.postDelayed(this, 30000);
}
catch (Exception e) {
e.printStackTrace();
}
}
};
}
//
private void CheckNetworkConnection(){
if( mNetworkHandler == null ){
mNetworkHandler = new Handler();
mNetworkHandler.post(mNetworkRunner);
Log.e("", "CheckNetworkConnection...");
}
}
You are doing a lot of time consuming work in UI Thread, which create problem. In this situation you should use AsyncTask.
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.
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) {
//do your time consuming task here
}
protected void onProgressUpdate(Integer... progress) {
//setProgressPercent(progress[0]);
}
protected void onPostExecute(Long result) {
//showDialog("Downloaded " + result + " bytes");
}
}
Once created, a task is executed very simply:
new DownloadFilesTask().execute(url1, url2, url3);
mNetworkHandler = new Handler() will make Runnable execute on UI Thread, you need HandlerThread
private void CheckNetworkConnection(){
if( mNetworkHandler == null ){
HandlerThread handlerThread = new HandlerThread("thread");
handlerThread.start();
mNetworkHandler = new Handler(handlerThread.getLooper());
mNetworkHandler.post(mNetworkRunner);
Log.e("", "CheckNetworkConnection...");
}
}
I've seen several other post about canceling an AsynTask, but I don't think any of them resolves the issues. Imagine this scenario:
public class TestTask extends AsyncTask<Void, Void, Object> {
#Override
protected void onCancelled(Object result) {
running = false;
Log.i("Test", "onCancelled");
}
#Override
protected Object doInBackground(Void... params) {
try {
Log.i("Test", "cancelling");
cancel(true);
Thread.sleep(5000);
Log.i("Test", "Past sleep");
} catch (InterruptedException e) {
Log.i("Test", "InterruptedException", e);
}
return null;
}
}
Imagine I'd like to cancel this long 20 second request in the middle of a download, for example if the server is responding slow to a json request. So the Thread.sleep(5000) could be a HttpGet request that I'd like to cancel. However the cancel method is marked as final so I can't override it and call get.abort(). The onCancel hook happens after the doInBackground and back on the UI thread. Checking for isCancel won't do me any good once the HttpGet request has started.
The way I solve this is to make an abort() method on my AsynTask and just call that.
public void abort() {
get.abort();
cancel(true);
}
but this seems to go against the Android grain a bit. Is there a better way to cancel the request?
In the docs for HttpGet, there is no mention of thread safety, so calling abort() the way you described will probably lead to undesired results (at best). What you could do is pass an HttpGet object in the constructor for your AsyncTask, or via a setter (as long you do this before you call AsyncTask.execute()).
You would have to check periodically inside of doInBackground() if the task has been cancelled:
#Override
protected Object doInBackground(Void... params) {
// start GET request
try {
Log.i("Test", "cancelling");
cancel(true);
Thread.sleep(5000);
Log.i("Test", "Past sleep");
if ( this.isCancelled() ) {
// abort GET request and/or stop doing other work
return null;
}
else {
// do what ever work you need to
}
} catch (InterruptedException e) {
Log.i("Test", "InterruptedException", e);
}
return null;
}
Source.
You can always call AsyncTask.cancel(true) whenever you feel the task should be stopped (AsyncTask.cancel())
I am not sure if this is applicable or not, but you could create another thread using an executor service that executes the download-task and keep checking for isCancelled() inside doInBackground() or until the future object returns, whichever happens first:
#Override
protected Object doInBackground(Void... params)
{
Callable<Void> downlaodTask = new Callable<Void>()
{
#Override
public Void call() throws Exception
{
// download task here
return null;
}
};
ExecutorService executor = Executors.newSingleThreadExecutor();
Future<Void> future = executor.submit(downlaodTask);
while(true) // check every second
{
try
{
future.get(1, TimeUnit.SECONDS); // wait until the download task finishes with 1 second as a timeout
break;
}
catch(TimeoutException e)
{
if(isCancelled())
{
executor.shutdownNow(); // or abort() or both
break;
}
}
}
return null;
}
I have been trying to download videos from a url, I have implemented my downloading method in the doInBackground() of asynctask, but the doInBackground method is taking a lot of time to get called(5-10 mins), I am using another asyntask to download image in the activity from which I am directed to download video activity and its working fine. My onPreExecute method is being called on time, but after that doInBackground takes almost 5-7 minutes to start. I will be really grateful for any help provided.
Here is mycode
btnDownloadLQ.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0)
{
try
{
new DownloadVideoTask().execute(videoURL);
}
catch(Exception e)
{
Log.e("Vidit_TAG","I got an error",e);
}
}
});
private class DownloadVideoTask extends AsyncTask<String, String, String>
{
#SuppressWarnings("deprecation")
#Override
protected void onPreExecute() {
super.onPreExecute();
showDialog(DIALOG_DOWNLOAD_PROGRESS);
}
protected String doInBackground(String... urls)
{
int i=0;
try
{
URL url = new URL (urls[0]);
InputStream input = url.openStream();
try {
//The sdcard directory e.g. '/sdcard' can be used directly, or
//more safely abstracted with getExternalStorageDirectory()
String root = Environment.getExternalStorageDirectory().toString();
File storagePath = new File(root + "/vidit");
storagePath.mkdirs();
OutputStream output = new FileOutputStream (new File(storagePath,title+".mp4"));
try
{
byte[] buffer = new byte[1024];
int bytesRead = 0;
while ((bytesRead = input.read(buffer, 0, buffer.length)) >= 0)
{
output.write(buffer, 0, bytesRead);
}
}
catch(Exception e)
{
Log.e("Vidit_TAG","I got an error",e);
}
finally
{
output.close();
}
}
catch(Exception e)
{
Log.e("Vidit_TAG","I got an error",e);
}
finally
{
input.close();
//tvTitle.setText("Completed");
}
}
catch(Exception e)
{
Log.e("Vidit_TAG","I got an error",e);
}
return null;
}
#SuppressWarnings("deprecation")
#Override
protected void onPostExecute(String unused)
{
dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
alertbox(title);
}
}
make sure no other asyncTasks are running , by cancelling them if needed.
on most android versions , asyncTask runs on a single background thread , and should only run small tasks .
in case the task might take too long (or there are multiple tasks) , consider cancelling them or use an alternative approach (like using executeOnExecutor as described on the API ) .
Late Answer but surely helps
If you are using min API level >=11 try this
//new YourAsyncTask().execute(); -- replace this with following line
new YourAsyncTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR); //use this
I'm facing the same issue in spite of it didnot happen every time.
You could use the tradtional Thread for an alternative and handle the UI changes yourself