If you’re trying to communicate with a web service or scrape any data from the web in your Android application, you might run into an exception like this:
E/AndroidRuntime(673): java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.example.helloandroid/com.example.helloandroid.HelloAndroidActivity}: android.os.NetworkOnMainThreadException
From Google’s documentation:
The exception that 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.
The fix
The problem here is simply that you need to make your web service calls (or what-have-you) on a separate thread. So, quite simply, you’ll need to look into how to do threading with Android. Unfortunately this can be a bit of a pain because you need to make your service calls on a separate thread, but you need to update the UI on the main thread. Normally this would require passing data between the threads, which involves handlers or other complexities. Luckily the Android platform provides the Async Task to handle this, which alleviates some of this complexity and may help you avoid some clutter in your code.
Useful documentation to migrate your network calls to threads (or Android’s Async Task)
Painless Threading (from the Android Developer docs)
Async Task (from the Android Developer docs)
Android Threads, Handlers and AsyncTask – Tutorial
Designing for Responsiveness (from the Android Developer docs)
