AsyncQueryHandler's call to onQueryComplete on ui thread? ( Android )

android, android-handler, android-loadermanager, multithreading

Solution

Is `onQueryComplete` called on UI thread?

It's called on the calling thread... so the thread on which you launched the `AsyncQueryHandler`.

Does it matter where `AsyncQueryHandler` is instantiated?

`AsyncQueryHandler` is a subclass of `Handler` that performs an asynchronous query (or insert, update, delete) to the `ContentResolver` and returns the result to the calling thread. `Handler`s are allowed to be associated with threads other than the main UI thread, and so are queries/transactions to the `ContentResolver`. Therefore, you should be allowed to call `AsyncQueryHandler` from a separate thread too.

That being said, doing so is probably not what you want for a couple reasons:

When you instantiate the `AsyncQueryHandler` on a separate thread, all subsequent callbacks will be returned to that calling thread. This is usually not what you want because it doesn't provide an easy means of syncing with the main UI thread, the thread that is responsible for creating your layouts and receiving your touch events.

You are already on a separate thread, so calls to the `ContentResolver` will already be asynchronous with respect to the UI thread.

And by the way, the documentation on `AsyncQueryHandler` doesn't mention anything about these points, but you can figure most of it out by reading the source code. The documentation for `Handler` (its immediate base class) explains the theory behind it too.

Problem

Original source