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I'm currently writing and android app, and I was using HttpClients and those classes. I spent 2 hours trying to fix some errors until I read a post that said that you cant do that operation in the main thread. So they suggested I use AsyncTask.

So My question is, how do I know which operations should be done in a different Thread? is there a list where I can read them?

Any information would be good, thanks in advance.

Christopher Francisco
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A NetworkOnMainThreadException is thrown when an application attempts to perform a networking operation on its main thread. This is only thrown for applications targeting the Honeycomb SDK or higher. Applications targeting earlier SDK versions are allowed to do networking on their main event loop threads, but it's heavily discouraged.

Some examples of other operations that ICS and HoneyComb won't allow you to perform on the UI thread are:

  1. Opening a Socket connection (i.e. new Socket()).
  2. HTTP requests (i.e. HTTPClient and HTTPUrlConnection).
  3. Attempting to connect to a remote MySQL database.
  4. Downloading a file (i.e. Downloader.downloadFile()).

If you are attempting to perform any of these operations on the UI thread, you must wrap them in a worker thread. The easiest way to do this is to use of an AsyncTask, which allows you to perform asynchronous work on your user interface. An AsyncTask will perform the blocking operations in a worker thread and will publish the results on the UI thread, without requiring you to handle threads and/or handlers yourself.

K_Anas
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The network exception is the only exception that will be thrown in android by blocking the UI-Thread. So you have to keep 3 rules in mind by programming in android.

Don't let the UI-Thread handle operations that will take more then 5 seconds to complete.

Don't let a broadcast receiver handle operations that will take more then 20 seconds to complete the onReceive ().

And don't handle network operations in the UI-Thread.

Steve Benett
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As other answers have said, Android is not thread safe, meaning:

  • You cannot manipulate the UI from a Background thread
  • You cannot do heavy tasks on the UI thread

Other operations of this sort could include processing large amounts of data/ database manipulation/HTTP requests/Network management. Really, I believe anything that doesn't require the UI thread but does involve large processing time should be moved to a seperate thread.

This makes logical sense, because if you were to do heavy processing, the user would feel a lag and User Experience would be compromised (and, ofcourse, could definitely be used to overload the system,etc.) Therefore, the system will kill the process and throw an error post-honeycomb.

As a result, you want to use an Async Task.

An Async Task really just opens a new Thread on which you can execute heavy processing or Network Connections. For Network Connections, I recommend the use of AsyncClients like this one that implement AsyncTask in an easier format for you to use. There are also libraries like UniversalImageLoader that will allow you to load Images into Grids/Lists.

I also highly reccomend you read the official Android documentation discussing this and there is a useful post on the Android blog about this as well. Lastly, I feel as if this post might be useful to you because it may include the error you encountered (Error because you performed the operation on the UI thread).

Other Resources I've found:

In conclusion, here is an example of an AsyncTask being used. (nicely put answer from @Graham Smith).

Community
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Kgrover
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Anything that takes a lot of time should be done in another thread. This includes large IO and network access. However I think only network access will throw an exception, anything else would cause an unresponsive UI. Although if you take way too long you'll trip a watchdog timer and the app will be killed.

Gabe Sechan
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As Gabe mentioned, you should do heavy tasks in separate threads.

there are two important things about android threads.

1 is the common threads..(the thread that do what you ask)

2 is the ui thread...(the thread that listens the user inreaction and draws ui)

you can change ui(Views act) only by ui thread.

on the other hand after honeycomb it is forbidden to do http requests in main thread. (it is called strict mode)

in short, any operation that blocks user interaction should be done in another thread.

i hope this helps you.

Ercan
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