Android :: Executing 2 Async Tasks
Dec 21, 2009
In the documentation, I read that it is not possible for executing 2 Async Tasks. If execute is called again, it should throw an exception.
The following is given under the heading of "Threading Rules", and i quote:
"The task can be executed only once (an exception will be thrown if a second execution is attempted.)"
I wish to understand the meaning of this statement.
Does this mean, that if i try and execute the same task twice (concurrently) when the first execution of the task was still going on...an exception will be thrown ? Will i need to wait for the completion of the first task, before i spawn a second task ?
A possible use case:
The user wishes to download a set of files. He clicks on the download button by providing the URL. When the first download is still going on, he wishes to download another file and provides another URL. Both these user actions are serviced by a DownloadTask, that extends the AysncTask.
If i wish to change this default behavior, is there a configuration option?
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Jun 4, 2010
How do you create unit tests for an Android activity that starts async tasks in onCreate? I would like to test the result of these tasks.
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Feb 23, 2010
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?
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Nov 22, 2010
I just have a concern about AsycnTask. If i have one activity which starts a async task. Now that activity goes in background and new activity gets opened & visible to us.
So the async task opened by previous activity stops or it still keeps going in background or it pauses or stops ?
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Aug 11, 2009
I'm making a App to send SMS trough VOIP providers from betamax.To send I just need to execute the URL
https://www.12voip.com/myaccount/sendsms.php?username=w​&password=x&from=y&to=z&text=some%20text
My app already creates the URL, but i cant understand how to execute.i think i have to make an HTTP request....but after a few hours after answers i still didn't understood.Can anyone help me execute that url with android?
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Aug 6, 2009
I want to change the start point of my machine, that is,when start on Android, it can run my app instead of "home" firstly,if it possible?
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Jul 14, 2009
I am developing a program that needs async socket. I am new to Android and Java. As I can see in the document, to write network program, I got Socket and SocketChannel, but it seems they are all sync socket, it means, I need an extra thread to call blocking read, write... and etc. Here comes the problem, my program is a chat room, the communicate is not linear, I have no idea when the server will send a message to me, if I read in that thread to wait message from server, but the user want to send message to server, the reading function blocked forever, if there is no incoming data, then the pending outgoing message will not be sent. That's why I need async socket. So my question is: How to write async socket under Android environment?
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Jul 28, 2010
I've got the URL of a .png image, that needs to be downloaded and set as a source of an ImageView. I'm a beginner so far, so there are a few things I don't understand:
1) Where do I store the file?
2) How do I set it to the ImageView in java code?
3) How to correctly override the AsyncTask methods?
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Sep 1, 2010
I am getting data from the server using AsyncTask. I need to update the data periodically.
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Oct 5, 2010
There is a strange out of memory error issue. I create a class to parse live streaming, and the class needs buffers to keep these raw data. Here are code snippets...
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Jun 16, 2009
Dose anyone know how to unable HOME KEY when program is executing?
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Mar 3, 2009
I have to execute the shell command
setprop net.dns1 xxx.xxx.xxx.xxx
from an android activity but i can't find a working way to do it. How can i execute this command from the application?
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Aug 16, 2010
For example, is there any way to define a service to run as 'system' UID or GID?Or any way to add your app to the 'system' group?
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Jul 16, 2010
What is the difference between Service, Async Task & Thread. If i am not wrong all of them are used to do some stuff in background. So, how to decide which to use and when?
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Jun 12, 2010
I read somewhere (and have observed) that starting threads is slow. I always assumed that AsyncTask created and reused a single thread because it required being started inside the UI thread.The following (anonymized) code is called from a ListAdapter's getView method to load images asynchronously. It works well until the user moves the list quickly, and then it becomes "janky".final File imageFile = new File(getCacheDir().getPath() + "/img/" + p.image);image.setVisibility(View.GONE);view.findViewById(R.id.imageLoading).setVisibility(View.VISIBLE);
(new AsyncTask<Void, Void, Bitmap>() {
@Override
protected Bitmap doInBackground(Void... params) {
try {Bitmap image;
if (!imageFile.exists() || imageFile.length() == 0) {
image = BitmapFactory.decodeStream(new URL(
"http://example.com/images/"
+ p.image).openStream());
image.compress(Bitmap.CompressFormat.JPEG, 85,
new FileOutputStream(imageFile));
image.recycle();
}image = BitmapFactory.decodeFile(imageFile.getPath(),
bitmapOptions);
return image;
} catch (MalformedURLException ex) {
// TODO Auto-generated catch block
ex.printStackTrace();
return null;
} catch (IOException ex) {
// TODO Auto-generated catch block
ex.printStackTrace();
return null;
@Override
protected void onPostExecute(Bitmap image) {
if (view.getTag() != p) // The view was recycled.
return;
view.findViewById(R.id.imageLoading).setVisibility(
View.GONE);
view.findViewById(R.id.image)
.setVisibility(View.VISIBLE);
((ImageView) view.findViewById(R.id.image))
.setImageBitmap(image);
}}).execute();I'm thinking that a queue-based method would work better, but I'm wondering if there is one or if I should attempt to create my own implementation.
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Nov 11, 2009
I have the following code...
CODE:.................
My mClient get method is a simple HttpClient execute with an output buffer to read the input stream, so it's very trivial. Everytime I execute this task UnknownHostException will be triggered which will in turn call onTaskError on my currect Activity, but I still get a RuntimeException, but I don't see why. Maybe it's because it's late and i've done about 12 hours of writing code so it's something simple I just can't see?
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Nov 2, 2010
In my android application i am using a loading screen,processed by Async task.In do in background of this task i would like to display a alert whenever an upgraded version exist in the server.
Could you please let me know if there is any way that i can do it in android.
The code is.
CODE:.................
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Apr 19, 2010
I am devoloping an application of image editor. I always do it by using the resources in the drawable carpet. Now I changed it to use the resources in the SD card. I don't change the code of the image access but the program always produce an error if I intent to set the value of a pixel. The program works correctly if I try to read the pixel but if I try to modify it fails. I think this is a permissions error but I added the following: <uses-permission android:name="com.android.editorImagenes.permission.WRITE_EXTERNAL_STORAGE"></ uses-permission> <uses-permission android:name="com.android.editorImagenes.permission.WRITE_OWNER_DATA"></ uses-permission> And everything remains exactly the same. I'm desperate. A thing happens is that if I try to do the scaling or rotating the image using a matrix postrotate, etc, the program works correctly and as of this moment I can use the SetPixel without causing error.
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Oct 10, 2010
I have been searching for an answer for this for some time now. I have an async task that downloads the database needed for my app, while this is downloading my app cant do anything as all the data it references is in this file, i have the app waiting for the file to be downloaded but i am attempting to show a progress dialog so the user knows something is happening while they wait for this to happen.however nothing shows up i have also tried directly calling ProgressDialog.show in the pre execute and moving this to the calling activity with no luck.
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Mar 5, 2010
I have a simple app and I'm using the AsyncTask to test out a background process, for clearness purposes I've opted to put my AsyncTask in a separate class rather than in an inner class, which where my problems begin, this is my AsyncTask. Code...
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Sep 22, 2010
I've a lot of initialization code in my main activity's onCreate(). When I launch my game, the screen goes black for a long time, then my game appears. I did logged some message at the start and end of onCreate() and found that onCreate() is executing its code while the screen is black. Sometimes the screen goes black for too long and phone shows a popup dialog prompting me to choose between Force close/Wait. Then when onCreate() is completed, my game appears. Choosing 'Wait' then dismiss the dialog.
I tried using progress dialog described in this article:
http://developer.android.com/guide/topics/ui/dialogs.html#ProgressDialog
But it doesn't work. The screen goes black for the same amount of time even after I use the progress dialog.
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May 26, 2010
I would like to a WebView to run some JavaScript before loading the rest of the page. This JavaScript should run in the same context of the page, just as if extra <script> content were added before any other <script> content. This is not possible with add Java script Interface() since I want to set up some instance variables, before the page scripts are run, so that the page scripts can use them.
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Aug 25, 2009
This link says that Android support Python, Lua and BeanShell Scripts, subsequently for Perl too. If it is so, is it possible for developers to write python scripts and call them in their standard Java based android applications?
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Feb 2, 2010
I am configuring wifi on my android based board using shell script. Now I want to execute the same script from android application. For that, I had used following code, but it didn't give any success till now,
I had executed same script from "adb shell" prompt and it works nicely.
Process exeCommands = Runtime.getRuntime().exec("/data/busybox/ board_script.sh");
is there anything else required than this?
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Feb 5, 2009
I try to create a mini player view on home screen and still use the music mediaplayback service by putting a IMediaPlaybackService aidl in home directory. the mini player can normally playback and control the music, but often meet the anr(com.android.music) and see below log.
CODE:....................
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Apr 24, 2010
I've got an Android activity which grabs an RSS feed from a URL, and uses the SAX parser to stick each item from the XML into an array. This all works fine but, as expected, takes a bit of time, so I want to use AsyncActivity to do it in the background. The line items = parser.getItems() works fine - items being the arraylist containing each item from the XML. The problem I'm facing is that on starting the activity, the ProgressDialog which i create in onPreExecute() isn't displayed until after the doInBackground() method has finished. i.e. I get a black screen, a long pause, then a completely populated list with the items in. Why is this happening? Why isn't the UI drawing, the ProgressDialog showing, the parser getting the items and incrementally adding them to the list, then the ProgressDialog dismissing?
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Jul 30, 2013
I have read quite a good books & blogs about the Background work process in Android and updating the UI.
I have learned few way like using a Service with Intent, Using AsynTask, Using a Bind Service with a Intent and so..
What is the rule of thumb using this, i mean when to use what?
I am just learning to code in JAVA & Android.
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May 22, 2010
How would I force the current thread to wait until another has finished before continuing. In my program the user selects a MODE from an AlertDialog, I want to halt executing of the program before continuing as the mode holds important configuration for the gameplay.
new AlertDialog.Builder(this)
.setItems(R.array.game_modes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
switch (which) {
case 0:
setMode(TRAINING_MODE);
case 1:
setMode(QUIZ_MODE);
default:
setMode(TRAINING_MODE);
break; ............
//continue loading the rest of onCreate();
contineOnCreate(); } })
.create().show();
If this is impossible can anyone give a possible solution?
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Apr 25, 2010
Trying to root my Hero for the first time. I am downloading the InstantRoot.apk.zip file, extracting it to InstantRoot.apk, which I then copy to the root folder of the phones sdcard.
When I try to execute it, using Astro, and choose "Open App Manager", it says "Could not open /sdcard/InstantRoot.apk as a APK file". What am I doing wrong? Is it maybe the unzipping that causes it?
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Apr 30, 2010
I am trying to execute a {public void} method in Service, from scheduled TimerTask which is periodically executing.This TimerTask periodically checks a condition. If it's true, it calls method via {className}.{methodName};However, as Java requires, the method needs to be {pubic static} method, if I want to use {className} with {.dot}.The problem is this method is for notification using Toast(Android pop-up notification) and Status Bar.But for this to work, the method must not have {static} modifier and resides in Service class.So, basically, I want background Service to evaluate condition from scheduled TimerTask, and execute a method in Service class.Can anyone help me what's the right way to use Service, invoking a method when certain condition is satisfied while looping evaluation?
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