I'm trying to handle the situation where the user loses their data connection during an Http request in an AsyncTask. Currently the AsyncTask will never finish executing if this happens and the app just stalls. I can't even check isCancelled() because the Http request just stalls out on one function call, so I can't implement a loop or anything.
I'm using the following in the UI thread but I can't figure out how to check if the task has been cancelled from within the task:
task = new LoginTask();
task.execute(this, mUsername, mPassword);
Handler handler = new Handler();
handler.postDelayed(new Runnable()
{
#Override
public void run()
{
if (task != null && task.getStatus() == AsyncTask.Status.RUNNING)
{
task.cancel(true);
}
}
}, 5000);
Since KSoap 2 is written in Java, an option for you would be to abstract one of the classes and manually set a timeout on the HttpConnection.
Based on our prior discussion, you will probably have to override the method that doesn't set a timeout on the connection and replace it with your own method and a connection that times out. Should be managable thanks to KSoap being open source! Good luck.
In order to stop processing, you would need to do a check on isCancelled() inside doInBackground(). If there are any reasonable places to do so in your doInBackground, you can add an if-statement. Otherwise you should consider setting a timeout on the http connection.
Related
This question already has answers here:
Wait for multiple AsyncTask to complete
(5 answers)
Closed 5 years ago.
I'm calling two AsyncTasks in parallel via this snippet in onCreate:
if ((DictMode.equals("TATOEBA")) || (DictMode.equals("SENTENCE"))) {
dictAsyncTask = new DictAsyncTask(DictionaryLookUp.this, "Tatoeba");
// dictAsyncTask.execute();
dictAsyncTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
if ((DictMode.equals("JUKUU")) || (DictMode.equals("SENTENCE"))) {
dictAsyncTask = new DictAsyncTask(DictionaryLookUp.this, "Jukuu");
// dictAsyncTask.execute();
dictAsyncTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
during onPostExecute I check whether any data gets retrieved and return from the startActivityForResult call via finish:
if (alldictStuff.size() == 0) {
...
Toast.makeText(DictionaryLookUp.this,"NOTHING FOUND ...",Toast.LENGTH_SHORT).show();
if ((DictMode.equals("TATOEBA")) || (DictMode.equals("JUKUU")) || (DictMode.equals("SENTENCE"))) {
Intent intentCard = new Intent(getApplicationContext(), CardView.class);
setResult(Activity.RESULT_OK);
finish();
}
but that's obviously flawed since I'm not checking whether both threads return no results, so what's the best way to check whether both threads are finished and returned nothing ? Do I have to use my own variables to track it or is there something neat/built-in I can utilize ?
This is mainly how you want to manage your business logic.
From your onPostExecute() either send intent or send broadcast message to main thread or maintain async task status list and mark finished for each task from onPostExecute().
You will need to call AsyncTask.get() method for getting result back and make wait until doInBackground execution is not complete. but this will freeze Main UI thread if you not call get method inside a Thread.
To get result back in UI Thread start AsyncTask as :
String str_result= new RunInBackGround().execute().get();
This is my first Android application and I am finding troubles with while loop, I am trying to use a while loop on my Android application but the application freezes.
What I'm trying to do is track the user location (using onlocationChanged) and keep querying on the location until the query returns a result. It's a GIS application so I am going to describe the application behavior:
the application keeps tracking the user position using a listener "onLocationChangedListener" and store it in a variable "myPosition". I am using a boolean"noResults=true". I will use a method "query(myPosition)" in the while loop, this method has a callback that when a result is found, and changes a boolean "noResults" to false. the loop will keep on until "noResults" is false (that means query's callback changed the boolean's value)
, here's what I did:
while(noResults)
{
//myPosition keeps changing
query(myPosition);
//query has a callback that when a result is found it changes noResults to false
}
I resolved the problem using a "Handler" that query the Feature Layer every 5 seconds, this stops the main thread from generating application not responding error:
Handler m_handler=new Handler();
Runnable m_runnable;
m_runnable = new Runnable(){
public void run() {
//query code here
m_handler.postDelayed(m_runnable, 5000);
}
};
m_handler.postDelayed(m_runnable, 0);
running while loop codes on the main thread freezes the UI, and makes all other processes pause making your app unresponsive use
Threads..
also note that the while loop you are running is running on a default Thread termed as the ui thread so in short run while loops on separate threads..
eg..
new Thread(new Runnable() {
#Override
public void run() {
// Your hard while loop here
//get whatever you want and update your ui with ui communication methods.
}
).start();
for ui communicating methods
View.post(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
Toast.makeText(getActivity(), "updated ui", Toast.LENGTH_LONG).show();
}
});
the view could be any views you are updating..
also like #TehCoder said you could use asynctask but asynctask is not meant for long workaflow work there are 3 of them but i can't recall the last one
Maybe you should use an AsyncTask? I'm not quite sure what your problem is tho.
Loop is not a problem in android (or any language).
There are two scenario might be reason for your freezing,
If you run network call in api, android throw error and crashes. You have to do network related calls in Aysnc Task ot threading
Use try throw catch and exception cases to avoid app crashing and better coding skill.
an Android 4+ app should perform a long running operation. This could be copying a million files from A to B for example. To not block the UI this operation runs in the background using an AsyncTask.
Assume that the operation needs some user feedback in the middle of the process to continue its work, e.g. "File XY already exists. Override, Irgnore or Rename?"
What is the best way to get this feedback from the user? Since the operation is running in a background thread one could not just present an AlertDialog (or something similar) since UI interaction is only possible in the main thread...
So for I came across these solution:
Ask for feeback before background threads starts, e.g. ask how to handle conflicts before starting to copy/move the files in the
background.
Do not handle conflicts but note them to ask the user
how to handle them after the operation is complete in a new
operation.
End the background operation on the first conflict, ask the user for feedback and continue a new background operation
I do not like any of these solutions. In the first case the user is asked for feedback even if there will be no conflict at all. The second solutions is not possible if the steps have to be processed in a specific order. The third solution would result in code that is very difficult to read/understand/maintain.
A good solution would be:
Stop the background thread
Marshal to the UI thread and get feedback from the user
Resume background thread and use feedback to continue the operation
Using GCD in Objectiv-C/iOS or async/await in C# this is not a big problem. But how can this be done in Android using AsyncTask?
Meanwhile I thought, that I found an answer here: Simply run myActivity.runOnUiThread(...) within doInBackground(...) and wait for it. Sounds good, but it does not work. The AsyncTask/background thread does NOT wait for the Runnable to finish:
private void copyFiles() {
CopyTask copyTask = new CopyTask (this);
copyTask.execute();
}
private class CopyTask extends CustomAsyncTask<Void, Void, Void> {
private doCopy;
#Override
protected Boolean doInBackground(Void... params) {
// Custom code, e.g. copy files from A to B and check for conflict
for (File file : allFiles) {
doCopy = true;
if (isConflict(file)) {
// Stop current thread and ask for user feedback on UI Thread
Runnable uiRunnable = new Runnable() {
public void run() {
// Pos 1. --> Execute custom code, e.g. use AlertDialog to ask user if file should be replaced...
doCopy = false;
synchronized (this) {
this.notify();
}
}
});
synchronized(uiRunnable) {
// Execute code on UI thread
activity.runOnUiThread(uiRunnable);
// Wait until runnable finished
try {
uiRunnable.wait();
}
catch (InterruptedException e ) {
e.printStackTrace();
}
}
}
// Pos 2. --> Continue work
if (doCopy)
copyFromAToB(File);
}
return null;
}
}
I would expect, that when a conflict is detected the Runnable is executed and and Pos 1 (code inside Runnable to resolve conflict) is executed BEVOR Pos 2 is reached. This is not the case. The Runnable is executed correctly but the AsyncTask does not wait for it to finish. The execution of doInBackground is continued without any interruption. It seems that doInBackground and the Runnable are executed in parallel (not suprising since they are executed on different threads) but why does doInBackground not wait?
Let's say in various points in my application, I create and fire off a new runnable like so:
new Thread(new Runnable() {
public void run() {
while(true) {
//do lots of stuff
//draw lots of stuff on screen, have a good ol time
//total loop processing time abt 1250-1500ms
//check for conditions to stop the loop, break;
} } }
Now, is there any way to terminate that thread midway through execution other than break; inside my while loop? I'd like to be able to kill it specifically and immediately from the parent thread, like, as in the event that the user just requested to load a different map. It feels clunky to insert an if (stopFlag) break; (set in parent thread) after every 5 or so lines of code.
I peeked at Runnable's and Thread's methods and I just can't see it. Someone know an awesome trick?
You may use AsyncTask and call cancel to cancel the thread.
Instead of while (true) you may check for a condition or a flag that would be changed properly when the Thread/Runnable should be stopped. This seems to be the suggested strategy since Thread.stop() has been deprecated.
You could use AsyncTask as suggested, which probably works best in this case. I believe you can also use the interrupt() method, which is preferred if good if you're not in Android, but still suffers from having to explicitly check if it is interrupted:
Thread t = new Thread(new Runnable() {
public void run() {
while (true) {
// do some stuff
if (isInterrupted()) {
break;
}
}
});
t.start();
// Whoa! Need to stop that work!
t.interrupt();
Im using a web service, so I want to use an async thread for the HTTP authentication request and another thread later to make additional service requests while my main thread runs.
Would like to see a good example of how to do this and how to show busy messages somehow in main app. How does the main app know when the thread finished? And what if my thread encounters exceptions, how do I deal with that?
HTTP requests are sent later, use the same cookies setup up by the first auth request, so will the later requests pick up the same cookies and just work?
Even better look here for the async part: Is there an accepted best-practice on making asynchronous HTTP requests in Android?
Look at here How to execute web request in its own thread?
AndroidAsync library I wrote to handle this automatically, it will run in the background and reinvoke onto the UI thread:
https://github.com/koush/AndroidAsync
// url is the URL to download. The callback will be invoked on the UI thread
// once the download is complete.
AsyncHttpClient.getDefaultInstance().get(url, new AsyncHttpClient.StringCallback() {
// Callback is invoked with any exceptions/errors, and the result, if available.
#Override
public void onCompleted(Exception e, String result) {
if (e != null) {
e.printStackTrace();
return;
}
System.out.println("I got a string: " + result);
}
});