Move _select encoding and decoding to threads.

[noamraph]

This includes 3 separate changes:

1. In FlutterContactsPlugin.kt, encode the _select results in the same thread in which fetching is done, instead of on the main thread.
2. In flutter_contacts.dart, decode on a separate dart isolate.
3. In example/main.dart, start fetching the contacts after the user presses the button.

There is still non-responsiveness. I think it's shorter.

The change in FlutterContactsPlugin.kt is reasonable - it just follows the implementation of MethodCallHandler, which is pretty small.

The change in flutter_contacts.dart is pretty ugly. I'm really not sure it's worth it.

The change in example/main.dart was useful because it allowed me to start profiling and then press the button.

I send this mostly as reference. If I were the maintainer, I would see how much the change in FlutterContactsPlugin.kt shortens the non-responsive time, and decide if it's worth the (not too big) added complexity. I would not merge the change in flutter_contacts.dart.

I hope this helps,
Noam

[aytunch]

Hi, I know this PR is old, but it could help the Android performance a lot for devices which have many contacts.
Will this be worked on any time soon? Thanks.

[joachim-quis]

Important Notice: Repository Reset for v2.0

This repository is being reset for a complete v2.0 rewrite of flutter_contacts. The existing v1 codebase and full git history will be preserved in the legacy_v1 branch.

What this means for your PR:

• This PR will become unmergeable after the reset
• If your change is a feature or fix that's still relevant for v2, please review the new codebase after the migration and consider re-implementing it against the new main branch

Note that v2 is a complete rewrite with many new features including full macOS support, comprehensive vCard import/export, SIM contacts, contact groups, account management, blocked numbers, ringtone assignment, and more. This PR may already be addressed in v2.

Thank you for your contribution, and apologies for the inconvenience!