In my app I need to download files from url locations. I want to display progress of the download in a dialogbox (or optionally in the notification area). I've come across several good resources on this subject (something like http://progrnotes.blogspot.com/2010/09/c-android.html). Unfortunately, all the examples don't provide a clear indication on how to properly cancel a download per the user's request. So my question is actually quite simple:
Given an asynctask which downloads the file in the background (with httpclient) and displays a dialogbox with download progress and a cancel button, how do I can cancel the download and stop the background task when the button is pressed?
I know killing threads is generally not a good idea, so I will probably need to work with a 'cancel'-variable in my background thread. How do I communicate a stop signal from the button to the asynctask?
Regards,
Ivo
Have your button call AsyncTask.cancel(true) and then check isCancelled() from inside doInBackground(Params... params). In this manner, you can communicate to the background thread that the download should be cancelled, and you can take the appropriate steps to stop it.
I would call cancel(true) on your AsyncTask object. This will interrupt your thread via normal interruption handling. You then can ask the AsyncTask if it isCancelled().
I would suggest you to go through this link for the dark-side of AsyncTasks: http://bon-app-etit.blogspot.in/2013/04/the-dark-side-of-asynctask.html .
Google has released a library called "Volley" that is used nowadays for faster and better networking .
It solves Bad points of AsyncTasks.
Canceling request using volley
Related
My Boss told me Not to use AsyncTask<> to hit a webservice. Standard told me use Threads to hit a webservice and then use the Handler to process the response from Thread. Can someone ellobrate how to use thread and handler to hit a API and then give the control back to the Handler , atleast a Tutorial if its possible or Code. What is handler, is there only one Handler in android Application? thnks
Please check it below example:
http://androidexample.com/Thread_With_Handlers_-_Android_Example/index.php?view=article_discription&aid=58
What you are actually trying to do with Thread and update your GUI with Handler is same as using AsyncTask. AsyncTask considers most of the aspects which are somehow difficult to manage. Obviously there are some downsides to use AsyncTask for more details have a look at my answer Down sides of AsyncTask
When to use?
If you're supposed to perform a short time request, then AsyncTask is perfect. However, if you need to get some data and display it but you don't want to worry about whether to download again if the screen is rotated and so on, you should consider using an AsyncTaskLoader.
If you need to download some big data, then you can consider using an IntentService.
I want to know which is better to download files, async task or service?
My app has eight buttons, which one starts one direfferent download (which download has ~10MB). When the user clicks on one button or more to download data is better to use async task or service?
Thanks!
In any case you should use AsyncTask because even service runs in the main (GUI) thread where no networking should be done. Whether to run the AsyncTask in a service or an activity depends on whether you want that download to continue in background.
all above answers have good points. but the life-cycle issue is the most important thing you should consider. for instance, let's say you use asyncTask. so the user starts downloading and suddenly he/she rotates the screen and because you tied the asyncTask life-cycle to activity another asyncTask operation will be kicked off and result in a compulsive 10mb download. so considering this you should use service and asyncTask together to maintain life-cycle issue and UI thread networking issue.
update: Intent-service is a better solution because it receives requests in its own thread and goes offline when it doesn't have anything to do
AsyncTask -- AsyncTask manipulate threads and/or handlers, if you can do that better with Looper and stuff why bother? AsyncTask is designed to be a helper class around Thread and Handler, and it should ideally be used for short operations (a few seconds at the most.).. how can you tell in production mode whether is not gonna take long? probably bad network, slow network,jammed network, phone restarting - and all these will probably make your downloading either corrupt or unfinished.. i am a user of apps, and i get pissed when i waste bundle on nothing..
if you ask me, use
Service
--Serviceis made to run irrespective of what app/screen is visible and make if communicate with the UI if only it is available if not continue with download and save it, AsyncTask does not constitute a generic threading framework. always use threads, its cool, we all love it.
I'm trying to make a web app using the WebView component. I need to modify the HTML before I show it to the user, so I tried to download it, modify it and the load it. I did this using the HTTP response and get classes and because of a series of exception I had to put them in an AsyncTask. Now the problem is that this solution works but it has a short delay because I have to wait for the Thread to end and then I can call the WebView.load() method either for the home and the other links. It is really ugly...do you have any solution to suggest me? Something without Async Tasks maybe?
The Android documentation states, that you should NEVER perform network operations on the main thread (otherwise, it will give you an exception).
Waiting for the AsyncTask to complete its background workflow is a natural process similar to think over the problem before giving the solution (your brain need to compute it in the background, if you will).
You will wait in any case. The server can't provide information instantly. But if you make request not in AsyncTask, it will block your application. And then android will offer to stop it. You dont need it. Instead of this you need to show something like process dialog.
Problem
Throughout my app I need to download files. In some cases I only need one-way communication, basically communicating with the Activity that a download has finished. In other cases, I need to be able to communicate to the background process to cancel the download, then relay back to the Activity once that task has been complete (two-way communication).
Stipulations
In all cases, a download is only associated with one Activity, so a Service seems unnecessary since I don't need to keep a download running in the background while the user does other things. The user is always blocked while the download is occurring. The download process should be Activity-independent (not specialized for one Activity...reuseable). It would be ideal to have one solution that meets all requirements.
Use cases
The two cases I have right now are as follows:
A user is shown a ProgressDialog while a file is being downloaded. Once the file completes downloading, the user proceeds to the next Activity. Progress does not need to be shown.
A user is shown a ProgressBar while a large file is being downloaded. There is a Cancel button to abort downloading the file. Pressing the Cancel button should signal to the background process to abort downloading the file, then inform the Activity once that action has been performed. Progress needs to be shown while downloading the file.
What I've tried
My original implementation was a separate class, ran in a thread, that passed in a Context that would broadcast progress. This allowed communication from the background process to the Activity, but not vise-versa.
I attempted a Service, but from various articles I read, determined my needs did not justify a Service, as the user needed to be blocked while the download was occurring. I had never implemented a Service before, so I also ran into communication problems (probably poor implementation).
What would be ideal
A two-way BroadcastReceiver. Is that possible? I like being able to register for a BroadcastReceiver if I want to get feedback from the background process, or not if I don't care. I already have a method in a class that takes in an InputStream and a File and makes the transfer, so that method is being reused everywhere that needs to download a file right now.
What you want to do is use an AsyncTask. Read these here on Stackoverflow:
Download a file with Android, and showing the progress in a ProgressDialog
and
Cancelling file download with httpclient and asynctask
Besides AsyncTask, you can also use Loaders.
They do pretty much what you need to do and I think they are available since android 1.6 with android compatibility package [related post]. I think this is your best option :)
I was wondering if it's possible to call specific methods defined within the AsynTask class from another class and/or service ?
In my specific case I have a Service playing some sounds, but the sound is selected from a List with available sounds...
When a sounds is selected it is downloaded from my home server, this takes some time (not much, let's say around the 3-4 seconds, the sounds/effects aren't big in size)...
So my problem at the moment is that I have a service to play those sounds, and when I select one I wanted to show a progressdialog... The way (if I understood correctly) is to use an AsyncTask, but the only thing the AsyncTask will do is telling my Service to play a specific sound from my server... So there is no "callback" from the service to the Asynctask...
How can I achieve that ?
How can I call a running AsyncTask, which sits in another class, and tell him all work is done and thus he can stop showing the ProgressDialog ?
Or am I over-engineering it and there are other ways ?
Thanks in advance...
I would use one asyncTask for every download. The download work is done in the doInBackground method. You can override the onPostExecute method to do all the work that should be done after the sound is downloaded. In your case I would think that would be hiding the progressdialog and telling the playing service that new music is available.
For more info on the AsyncTask have a look at the android documentation.
Actually, what I think you want is the opposite. The AsyncTask should be used to perform the long running process, not to display the progress dialog. In fact, you should not use the task's background process to access any part of the UI. So what you would do is display a dialog, start your task, then have the task dismiss the dialog in its onPostExecute method, which can manipulate UI components.