Embedded Flutter application communication with parent application

These examples show communication between the Flutter Application and the host / native application via message channels. The same Flutter code is used for all three embeddings with a minor switch statement for Web communication.

Message flow

This application uses message channels for mobile platform/Flutter communication. Both Flutter and Native can initiate an increment operation. The native side always receives a message from Flutter after an increment operation has occured.

graph TB;
    subgraph host
        HostControl[Control and UI Listener]
        HostChannel[Message Channel]

        HostChannel2[Message Channel]
        HostListener[Message Listener]
    end

    subgraph flutter
        FlutterControl[Control and UI Listener]
        FlutterChannel[Message Channel]

        FlutterChannel2[Message Channel]
        FlutterListener[Message Listener]
        Counter
    end

    FlutterControl--increment()-->Counter--{action:incremented}-->FlutterChannel2-.{action:incremented}.->HostChannel2-->HostListener

    HostControl--increment()-->HostChannel-."{action:incremnt}".->FlutterChannel

    FlutterChannel--"{action:increment}"-->FlutterListener--increment()-->Counter

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Platform-specific implementations

Additional details are available for each platform implementation

Platform
Web application with message communication between Flutter and Web
Android application with message communication between Flutter and Android
iOS application with message communication between Flutter and Android

Mobile Native communication

Communication between the Mobile native code and Flutter happens over platform channels. Web commnication happens via window messaging

Flutter Channel types

There are three native platform channel types. V1 of this application uses the Message Channel

Channel type and Flutter class	Description	Flutter Native	Native Flutter	Return
Method Invocation	Invoke method on the other side	Yes	Yes	Via result
Message	Sends a message to a remote listener	Yes	Yes	Via reply
Event	Streams and sinks. Events can flow in both directions	Yes	Yes	N/a

FlutterMethodChannel, FlutterEventChannel, FlutterBasicMessageChannel

Dart/Flutter, Android and iOS have corresponding channel classes for each channel type. The three platform channel implementation classes in Flutter, iOS and, Android are:

The V1 demonstration code in this repository implements native communication via a message channel.

Flutter Class	iOS Class	Android Class
MethodChannel	FlutterMethodChanel	MethodChannel
EventChannel	FlutterEventChannel	EventChannel
BasicMessageChannel	FlutterBasicMessageChannel	BasicMessageChannel

Method Channel Codecs MethodCodec

Method channels a method on the opposite side. Method channels use MethodCode implementations.

Flutter Codec Class	iOS Codec Class	Android Codec Class
MethodCodec Interface	...	...
StandardMethodCodec	FlutterStandardMethodCodec	StandardMethodCodec
JSONMethodCodec	FlutterJSONMethodCodec	JSONMethodCodec

Message Channel Codecs

Message channels use MessageCodec Implementations. Messages are a single payload with an optional return value. Uses codecs shown below.

Flutter Codec Class	iOS Codec Class	Android Codec Class
MessageCodec Interface	...	...
StandardMessageCodec	FlutterStandardMessageCodec	StandardMessageCodec
BinaryCodec	FlutterBinaryMessageCodec	BinaryCodec
JsonMessageCodec	FlutterJSONMessageCodec	JSONMessageCodec
StringCodec	FlutterStringCodec	StringCodec

Event Channel

Event channels are continuous broadcast streams that use a MethodCodec.

Flutter Codec Class	iOS Codec Class	Android Codec Class
See MethodCodec	See MethodCodec	See MethodCodec

V1

This is the shortest path with as little code as possible.

1. Flutter fills up the entire screen for the iOS and Android applications. There are no native controls to generate the increment messages
2. This uses a classic single channel specifying the action in a field in the JSON. Native applications typically do one message per channel and have one channel for each message type