[Breaking Change] iOS: FlutterEngine, FlutterViewController no longer FlutterBinaryMessengers

[Aaron Clarke]

Code effected

iOS code that sets up channels manually (not plugins).

PR

https://github.com/flutter/engine/pull/9419

Old architecture

New architecture

Justification

The old architecture could lead to inadvertent retain cycles.  For example:

FlutterEngine *-- FlutterPlugin *-- FlutterMethodChannel *-- FlutterEngine

This is of particular interest to the add-to-app flow.

Relevant Issue:

https://github.com/flutter/flutter/issues/26007

Migration

Old Code:

[FlutterMethodChannel 

    methodChannelWithName:@"foo" 

    binaryMessenger:flutterViewController]

New Code:

[FlutterMethodChannel 

    methodChannelWithName:@"foo"

    binaryMessenger:flutterViewController.binaryMessenger]

Plugins:

Plugins usually get the binary messenger from the FlutterPluginRegistrar (ex. [registrar messenger]), so they shouldn't be affected.

In Closing

This proposal should be an easy migration that shouldn't affect many people.  Let me know if this would be a problem for you.