Present full-screen native SDK UI from Flutter and return a result

What's really being asked

This question evaluates whether you can distinguish between inline native embedding and full-screen native presentation in Flutter, and whether you know how to bridge asynchronous UI flows across the platform channel boundary. The interviewer cares about your understanding of MethodChannel bidirectional communication, native view controller and activity lifecycle management, and correct API selection.

The full answer

First, state that MethodChannel is the correct integration point because PlatformView is designed for rendering native views inside the Flutter widget tree and cannot present a modal UIViewController or start a full-screen Activity outside of that tree. Second, describe the async handshake pattern where Dart invokes a platform method to request presentation, the native side stores the FlutterResult or MethodChannel.Result reference, presents the SDK UI, and later invokes that stored reference with the payload after dismissal. Third, mention lifecycle safety such as presenting on the rootViewController on iOS or using the current Activity on Android, and guarding against engine detachment or activity destruction during the native flow. Fourth, explain result serialization by converting the native SDK object into a Map or JSON structure that crosses the channel, plus error handling for cancellations or SDK failures.

The mistakes people make

The biggest red flag is suggesting PlatformView for a full-screen native controller, which reveals a fundamental misunderstanding of the embedding API. Another red flag is attempting to return the selected item synchronously from the platform method instead of using the async result callback. Proposing to reimplement the third-party SDK UI in Flutter widgets is also wrong because the question explicitly provides a native SDK that must be used as-is.

What usually comes next

The interviewer may ask how you would handle Android configuration changes that destroy the Activity while the native SDK is showing, or how you would surface SDK errors through the channel as a PlatformException. They might also ask whether you would use Pigeon for type-safe channel contracts in production, or how you would mock the native layer for widget tests on the Dart side.

A concrete example

Imagine integrating a native document scanner SDK. On the Dart side, you call scanDocument through a MethodChannel and await a Map result. On iOS, the platform handler in a plugin or app delegate instantiates the SDK ScannerViewController, configures it, and presents it on the topmost UIViewController. When the scanner delegate fires didFinishWithResult, the handler calls the stored FlutterResult with a dictionary containing documentPath and confidenceScore. On Android, the handler launches the SDK ScannerActivity via startActivityForResult from the current Activity. In the plugins onActivityResult override, you extract the URI and metadata from the intent, then return them through result.success.