Just to spell out something explicitly:
The main thread is basically the UI thread.
So saying that you cannot do networking operations in the main thread means you cannot do networking operations in the UI thread, which means you cannot do networking operations in a *runOnUiThread(new Runnable() { ... }* block inside some other thread, either.
(I just had a long head-scratching moment trying to figure out why I was getting that error somewhere other than my main thread. This was why; this thread helped; and hopefully this comment will help someone else.)