How to pass a message from Flutter to Native?

[Adam Hurwitz]

How would you pass info from Flutter back to Android/Native code if needed to interact with a specific API / hardware component? 

Are there any Event Channels that can send info the other way or something similar to a callback?

1. The platform_channel documentation points out "method calls can also be sent in the reverse direction, with the platform acting as client to methods implemented in Dart. A concrete example of this is the quick_actions plugin." I don't see how the native side is receiving a message from Flutter in this instance.

2. It looks like a BasicMessageChannel’s send() method can be used to send "the specified message to the platform plugins on this channel". Can anyone provide a simple implementation example of this?

[Mikkel Ravn]

Hi Adam,

You'll find a simple example of Flutter-to-platform communication in the examples folder in the Flutter repo (Flutter sender, Android receiver, iOS receiver).

For many more examples of two-way communication between Flutter and the Android/iOS platform, take a look at our plugins repo. Most of these use MethodChannels for the communication (irrespective of direction), BasicMessageChannel being a bit too low level for common usage.

Cheers,

Mikkel

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Mikkel Nygaard Ravn

Software Engineer

[Adam Hurwitz]

Thanks for the specific code example Mikkel! 

Can you send information like a network response in the Flutter sender to an Android receiver instead of a method call?

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Mikkel Nygaard Ravn

Software Engineer

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ASH

[Mikkel Ravn]

Not entirely sure what you are looking for. Sending information from Flutter to platform-specific code can be done use MethodChannels, by passing in a second argument after the method name:

myMethodChannel.invokeMethod('someMethod', someInformation);

All you need is to package your information using the allowed types for the channel.

On the platform side, you'd register a method call handler with the channel. When called, that handler will receive a MethodCall object whose arguments field hold the information sent from Flutter. See e.g. the url_launcher plugin for an example (Android, iOS).

[Adam Hurwitz]

I will have to dive into the sample code more in depth to test my understanding.

Thanks for the specific example! 

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Adam  

[ged...@gmail.com]

You said you wanted to connect it to a network.

What you can do is pass protobuf as a byte[] between flutter and java / swift.
Then you can use the protobuf to codegen the dart code too if you want.

You can then use that same protobuf with grpc to do network communications.

Not sure if this helps. I was using json but am trying out protobufs because it's quite a bit faster at runtime.

[ged...@gmail.com]

https://pub.dartlang.org/packages/protoc_plugin

[TruongSinh Tran-Nguyen]

Hi, I happen to write an article about using Protobuf with Platform channels https://medium.com/@i_2412/flutter-platform-channels-with-protobuf-e895e533dfb7