Android :: AsyncTask On A Button
Jul 15, 2009
My application parse an xml file dans display data in a list view. On start of application i load data using an AsyncTask. A Progress Dialog is display during the load. This part works fine.A button in the application make it possible to reload the data. I would like to run the AsyncTask but the sytem say i can't alter view in other thread. I have also read an AsyncTask can't be run another time So i would like to know what is the best way to do this and not to have the "application not responding" message.
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Jul 28, 2010
I'm trying to figure out the correct way to create an AsyncTask to retrieve some data from the internet and then to take that data and bundle it up in an Intent and pass it to a new activity(A list display). So in the first activity I just have an EditText and Button. In the event of an OnClick the task should be called and when it is finished the data should be bundled inside an Intent and passed to the next Activity. The problem is when I take the results from onPostExecute and set them to an instance variable of the main activity, that instance variable is still null when the task is complete. Here is the barebones version of the code:
CODE:...........
When I debug the application I see onPostExecute does contain a valid PlacesList full of results, so why is the instance variable places set to null after the task is executed? I am going about "returning data" from an AsyncTask incorrectly?
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Apr 6, 2010
I am working on a simple application (studying purposes) which list all the files from a selected folder. On top of that I would like to have a search feature where the user can search for files (the code for that is already in place). Now, I was thinking about having the search running in the background somehow, whilst the user can still navigate, create folders, copy, sort and do other stuffs normally. When the search finishes the user would get a notification and then could click on it and go to that activity (It ideally should be the same ListView I already use for browsing the files, I would just need to update the Adapter there with the latest processed data after clicking in the notification). What's the best answer for that? Threading or AsyncTask?
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Dec 27, 2009
Can anyone point me to a good example where a AsyncTask queries a local SQLite database and then updates the UI successfully. I have a database which I query using doInBackground... create a new custom SimpleCursorAdapter (overriding onViewBind), return the adapter (SimpleCursorAdapter), then in postExecute() create ListView adapter which is set to the the SimpleCursorAdapter, that was returned, then I set the listview adapter using SetAdapter(adapter);...
For some reason I throw an exception on fillWindow.java:200....
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Aug 9, 2010
I know this is not how an async task should behave but my question is how to "block" the user while executing it.My need is the following: I have my own backup/restore process and I have an async task to run these two actions. The backup is fine, I can warn the user when the backup is done and that's just fine But my problem is about the restore process. When the user click on restore he shouldn't be able to make any change in the application (and anyway don't want to because he would lose all his changes).I understand that having the user blocked while restoring (or maybe with a progress bar) is not a best pratice but I do not see any other possibility in this context.
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Apr 9, 2010
I know how to use AsyncTask in a standard manner to manage operations that are in the background in relation to a UI thread.However,I want to run a task in the background which might run for a very long time under certain circumstances. In these cases, I would like to force the background task to fail if it runs for an excessive amount of time.I know that I can invoke the "get(long timeout, TimeUnit unit)" method of AsyncTask in my UI thread in order to terminate my background task if it runs too long. However, in that case, my UI will block while this "get()" command is waiting.There are probably other drawbacks to directly calling "get()" in this manner, not the least of which being an evil interaction with the "done()" method of AsyncTask's contained FutureTask object, which itself is calling "get()" at least this is what I see when I look at the source code for AsyncTask.
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Jul 5, 2010
I have an activity that needs to do some stuff in the background. When the background is done, I want it to load a new activity.I can successfully kick off the async task and using using ViewSwitcher I can show a nice progress dialog.However, when the user hit 'back' or 'close' from the new task, I want them to see the main screen of this task again. So, I use the showPrevious() after I start the new Activity, but I see the screen switch from the loading window back to the main window BEFORE the new Acitivity is launched.How do I get it to switch after the new activity, or when they come back from the new activity?I tried onRestart() and onResume() but both of them seem to give me a view of -1 that I couldn't do much with.
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Sep 20, 2010
I'm running a network service within an ASyncTask. I want to be able to time the task, and after a certain period of time interrupt it.Is there a simple way to do this? Basically, when the doInBackground() methods starts, I want to say "If it hasn't completed in 30 seconds, do something else".
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Jul 29, 2009
I'm developing a game based on SurfaceView and a game thread for the whole game thing.Now I want to do some HTTP requests triggered on events inside the thread. They should of course be asynchronous, so the game doesn't stop. I found AsyncTask to be a neat way to do this but I'm having trouble implementing this at the moment. Maybe I misunderstood the concept of AsyncTask,I don't know it just drives me nuts as I read docs and blogs and still I don't get it. So sorry if that's a dumb question but I'm mad of thinking about it.
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Mar 13, 2010
while debugging and app that uses AsyncTask to record audio and update UI I noticed that everytime that an AsyncTask object ends running (finishes doInBackground and onPostExecute or on Cancelled it´s thread stays alive (running status).At least for me that should not be the behavior of the class since the doInBackground task may not stay running forever (as an example the android manual says that a status bar should be updated by an asynctask, and it won´t last for the whole app running time).Is there anything I´m missing, as a method to destroy it, or should I just ignore and keep creating threads as I need and the VM will handle them as it needs resources?
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Jul 18, 2010
When I try to compile to following code, I get two errors:
Description Resource Path Location Type
Syntax error on token "void", invalid Expression AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 19 Java Problem
Description Resource Path Location Type
The type AsyncTask is not generic; it cannot be parameterized with arguments AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 25 Java Problem
CODE:............
Obviously AsyncTask IS a generic (http://developer.android.com/reference/android/os/AsyncTask.html#execute so why do i get those errors?
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Jan 7, 2010
In order to get XML data from a server repeatedly, I'm attempting to use AsyncTask and Timer as per Mark Murphy's suggestion. I get the following error:01-07 16:11:26.705: ERROR/AndroidRuntime(729): Caused by: java.lang.Runtime Exception: Can't create handler inside thread that has not called Looper.prepare()I'm using SDK 1.5 with Eclipse on Windows.I've looked in documentation, on StackOverflow and in the Android Developers group, but I'm not clear what's causing the error or how to fix it.I can get the data once - i.e. without Async and Timer - and parse it via SAX without problems.s: I'm quite new to Android.
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Apr 10, 2010
My program was going wonderfully. It is a search engine that connects to our back end database by sending Get requests to our server and displays the results. I've managed to get it to query my server and back end database, return results using JSON, return the first headers and pour them into a ListView widget in the main activity. Then when the user clicks on one of the headers it then sends another query from a sub-activity. It then parse those results and format them neatly into a WebView embedded into the sub-activity.
All this works perfectly. That is until I come to make a second query on the main activity. Listed below is my stack trace of where the error happens. I think I know why this is happening, but obviously not clearly understanding it.
I think it is because I am trying to call AsyncTask again. I remember reading that the AT can only be called once, but I presumed quite wrongly that this meant you can not do concurrent calls. I thought that once an AT had done it's task it was cleared and then could be called again, but this does not seem to be the case. Is it because of AT attempts at more than one call ? If so, would I be better changing that section into a Handler with a Runnable on the main activity?
-----Stack Trace----
CODE:.....................
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Dec 16, 2009
I'm working out my first multi-threaded application using Android with the AsyncTask class. I'm trying to use it to fire off a Geocoder in a second thread, then update the UI with onPostExecute, but I keep running into an issue with the proper Context.
I kind of hobbled my way through using Contexts on the main thread, but I'm not exactly sure what the Context is or how to use it on background threads, and I haven't found any good examples on it.
Here is an excerpt of what I'm trying to do:
CODE:...........
It keeps failing at the sixth line there, because of the improper Context.
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Feb 12, 2010
When using ThreadPoolExecutor can I use AsyncTask as the Runnable in my queue? Or does this defeat the purpose?
CODE:.....................
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Mar 5, 2010
Im using HTC Hero with HTS sense. Im experience that sometimes AsyncTask not will run doInBackground method on execute();
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Mar 26, 2010
I'm confused as to when one would choose AsyncTask over a Handler. Say I have some code I want to run every n seconds which will update the UI. Why would I choose one over the other?
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Oct 12, 2010
Tell about the "asynctask" used in android application. Currently I am working on an application where I have to create a Class in which I have to just get the response of any particular URL given. I this particular class I was told to perform this task by making use of "asynctask".
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Nov 2, 2010
I'm having a problem with the AsyncTask class. It seems like my task stops working after creating 4 or 5 tasks.
Im having 2 activities. MainActivity which only holds a button that starts a second activity called ImageActivity.
ImageActivity is very simple. it got an onCreate that sets the layout, and then it starts a new AsyncTask that loads an image from the internet. This works fine the first few times. But than it suddenly stops working. The onPreExecute method is run every time, but not the doInBackground method. I have tried to simplify the doInBackground with a sleeping loop, and the same thing happens. I cant understand this behavour since the asynctask is both canceled and set to null in the onDestroy method. So every time i start a new ImageActivity, i also create a fresh AsyncTask.
I recreate the ImageActivity and the task by hitting the back button, and than clicking the button on the MainActivity.
UPDATE: Code that starts the ImageActivity (inside a button onClickListener)
CODE:...........
The code above starts this activity
CODE:.............
UPDATE:
I have tested using a combination of traditional Threads and runOnUiThread method, and it seems to work better. Now the thread runs every time.
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Nov 24, 2010
I've been using my Activity class to access my DB which made my program freeze sometimes.
So I decided to use AsyncTask instead to handle the DB.
My problem is I don't know how to instantiate my SQLite DB "TheDB" from AsyncTask's class
CODE:.............
This worked fine on the Activity class, but it I dont know how to use it here
TheDB's constructor is TheDB(Context context) but this class is not a "context" so how can i use my DB here?
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Apr 11, 2010
I don't understand why I'm getting this error. I'm using AsyncTask to run some processes in the background. I have:
protected void onPreExecute()
{
connectionProgressDialog = new ProgressDialog(SetPreference.this);
connectionProgressDialog.setCancelable(true);
connectionProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
connectionProgressDialog.setMessage("Connecting to site...");
connectionProgressDialog.show();
downloadSpinnerProgressDialog = new ProgressDialog(SetPreference.this);
downloadSpinnerProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
downloadSpinnerProgressDialog.setMessage("Downloading wallpaper...");....
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Sep 10, 2010
Implementing a service to handle connection changes and downloads. The service handles a queue of AsyncTasks, each representing a "download task". This way, we can cancel/pause tasks when connection drops, and also restore them when connection is reestablished. Since the threads AsyncTasks are run are not deterministic, how many ATs should I execute() at the same time?
I've read that I shouldn't reuse tasks. How can I achieve this pause->resume functionality then? Should I tell the thread to sleep? Should I make a no-op while if connection is down? I was trusting the cancel(true) method, which I've read is not reliable either.
My main DownloadTask is a subclass of AsyncTask that returns a new AsyncTask to be called when the connection is restored.
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Jul 21, 2009
I execute this async task in my application, I don't understand why my progress dialog and all application freeze. Insert in doInBackground put one hundred or so entity in database.
In other case (but it's fisrt time with sqlite).
I use AsyncTask and I have no problem.
CODE:.................
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Jan 21, 2010
According to my research, which includes reputable sources (Mark Murphy et al), the most preferred way of polling a remote source and presenting said data to the user is by creating a service and using AsyncTask within that service to do the polling. I have done that.But, when I read the docs there seem to be several "Threading Rules" that conflict with this way of doing things: "The task instance must be created on the UI thread." and "execute(Params...) must be invoked on the UI thread." As stated, I have created the task instance on the Service thread (not the UI thread). Am I missing something? Also, when the AsyncTask finished, I sent out a Broadcast on onPostExecute, which is then picked up by the Activity, telling it to retrieve the final value again from the service (since I couldn't obviously update the UI from the service). I couldn't figure out any other way to return the result of the AsyncTask. Is this the correct practice?
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Oct 27, 2009
I ran into some trouble trying to use a Looper inside an AsyncTask (its doInBackground method). Everything works fine until new Tasks are being created by AsyncTask.sThreadFactory, but once I reach the AsyncTask.CORE_POOL_SIZE limit and AsyncTask begins to recycle the threads, sending messages to my looper (created inside doInBackground) results in a MessageQueue RuntimeException: "sending message to a Handler on a dead thread".
The code I tried was:
CODE:....................
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Jul 21, 2010
Android documentation says that AsyncTask postExecute() is called on the UI thread. I was under the impression that postExecute() was called from the Thread where execute() was called : I have been using an AsyncTask in a background Service with its own thread, and postExecute() was called in the service thread, not the main thread. However, I recently had an issue with the postExecute() not being called at all, while an exception was thrown : " sending a message to a Handler on a dead thread". How is it exactly :
- shall AsyncTask be used ONLY from the main thread ?
- if not, in which thread postExecute() is supposed to be called : always the UI thread, or the execute() calling thread ?
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Sep 10, 2010
Is there a standard pattern for handling a running AsyncTask with screen rotation? My AsyncTask runs for about 10 seconds. I could call AsyncTask.cancel in the Activity's onDestroy method and restart the task in onCreate but that would waste cycles, bandwidth, and user time. I'm guessing there is a better way.
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Dec 19, 2009
I'm running a pretty weird setup:
AsyncTask1.class -> AsyncTask2.class ->AsyncTask3 (inner class of AsyncTask2) ->NDK call (this one takes a long time).
Since the NDK takes so long, I want to give users the option to kill the NDK call so that they can actually use the app. Basically, I keep references of all the asynctask instances and I do:
aSyncTask1.getAsyncTask2().getAsyncTask3().cancel(true);
The true means mayInterruptIfRunning
But, lo and behold, the NDK process is still running. I don't care how its done, but I need that NDK process to die when I ask it to. I'm thinking about kill-9 it through a popen call..
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Aug 18, 2010
I am facing an issue with AsynsTask in my Application. I really do not understand the reason of it happening.
The issue is "The application works perfectly usually, now when any of the activity is displayed on the screen and I keep my device idle for a longer period of time. Then when I make the keyguard on the view of the last active activity is displayed to me. But as soon as I click on any component below mentioned exception is thrown. If the device is not kept for a longer period of time then there is no problem as such. The application makes http connection in onResume of most of the activities. I did this since every time the user comes to particular view then he should get the updates lists of posts from the webservice"
CODE:................
Let me know the reason behind this error and any solution to this?
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Aug 18, 2009
AsyncTask blocks exceptions? Please see the below code. My "getOffersStatus" function catches certain exceptions and show them in a AlertDialog. But instead of getting my custom exceptions message I get default error dialog "The application ... has stopped unexpectdly. Please try again".
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