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If your device doesn’t have a battery,
it displays ‘Battery level not available’.<topic_end>
<topic_start>
Typesafe platform channels using Pigeon
The previous example uses MethodChannel
to communicate between the host and client,
which isn’t typesafe. Calling and receiving
messages depends on the host and client declaring
the same arguments and datatypes in order for messages to work.
You can use the Pigeon package as
an alternative to MethodChannel
to generate code that sends messages in a
structured, typesafe manner.With Pigeon, the messaging protocol is defined
in a subset of Dart that then generates messaging
code for Android, iOS, macOS, or Windows. You can find a more complete
example and more information on the pigeon
page on pub.dev.Using Pigeon eliminates the need to match
strings between host and client
for the names and datatypes of messages.
It supports: nested classes, grouping
messages into APIs, generation of
asynchronous wrapper code and sending messages
in either direction. The generated code is readable
and guarantees there are no conflicts between
multiple clients of different versions.
Supported languages are Objective-C, Java, Kotlin, C++,
and Swift (with Objective-C interop).<topic_end>
<topic_start>
Pigeon example
Pigeon file:
<code_start>import 'package:pigeon/pigeon.dart';
class SearchRequest {
final String query;
SearchRequest({required this.query});
}
class SearchReply {
final String result;
SearchReply({required this.result});
}
@HostApi()
abstract class Api {
@async
SearchReply search(SearchRequest request);
}<code_end>
Dart usage:
<code_start>import 'generated_pigeon.dart';
Future<void> onClick() async {
SearchRequest request = SearchRequest(query: 'test');
Api api = SomeApi();
SearchReply reply = await api.search(request);
print('reply: ${reply.result}');
}<code_end>
<topic_end>
<topic_start>
Separate platform-specific code from UI code
If you expect to use your platform-specific code
in multiple Flutter apps, you might consider
separating the code into a platform plugin located
in a directory outside your main application.
See developing packages for details.<topic_end>
<topic_start>
Publish platform-specific code as a package
To share your platform-specific code with other developers
in the Flutter ecosystem, see publishing packages.<topic_end>
<topic_start>
Custom channels and codecs
Besides the above mentioned MethodChannel,
you can also use the more basic
BasicMessageChannel, which supports basic,
asynchronous message passing using a custom message codec.
You can also use the specialized BinaryCodec,
StringCodec, and JSONMessageCodec
classes, or create your own codec.You might also check out an example of a custom codec
in the cloud_firestore plugin,
which is able to serialize and deserialize many more
types than the default types.<topic_end>
<topic_start>
Channels and platform threading
When invoking channels on the platform side destined for Flutter,
invoke them on the platform’s main thread.
When invoking channels in Flutter destined for the platform side,
either invoke them from any Isolate that is the root
Isolate, or that is registered as a background Isolate.
The handlers for the platform side can execute on the platform’s main thread
or they can execute on a background thread if using a Task Queue.
You can invoke the platform side handlers asynchronously
and on any thread.info Note
On Android, the platform’s main thread is sometimes
called the “main thread”, but it is technically defined
as the UI thread. Annotate methods that need
to be run on the UI thread with @UiThread.
On iOS, this thread is officially
referred to as the main thread.<topic_end>
<topic_start>
Using plugins and channels from background isolates
Plugins and channels can be used by any Isolate, but that Isolate has to be
a root Isolate (the one created by Flutter) or registered as a background
Isolate for a root Isolate.The following example shows how to register a background Isolate in order to
use a plugin from a background Isolate.<topic_end>
<topic_start>