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Updated the platform channels documentation for background isolate channels #7592

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Updated the platform channels documentation for background isolate channels #7592

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36f297c
Updated the platform channels documentation to show how to use plugins
gaaclarke Sep 26, 2022
4020447
Update src/development/platform-integration/platform-channels.md
gaaclarke Sep 28, 2022
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39 changes: 32 additions & 7 deletions src/development/platform-integration/platform-channels.md
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Expand Up @@ -969,13 +969,13 @@ types than the default types.

## 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, invoke on the root `Isolate`.
The platform side's handlers can execute
on the platform's main thread or they can execute on
a background thread if using a Task Queue.
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 when the Task Queue API is available;
otherwise, they must be invoked on the platform thread.
Expand All @@ -989,6 +989,31 @@ otherwise, they must be invoked on the platform thread.
referred to as [the main thread][].
{{site.alert.end}}

### 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`.

```dart
import 'package:flutter/services.dart';
import 'package:shared_preferences/shared_preferences.dart';

void _isolateMain(RootIsolateToken rootIsolateToken) async {
BackgroundIsolateBinaryMessenger.ensureInitialized(rootIsolateToken);
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
print(sharedPreferences.getBool('isDebug'));
}

void main() {
RootIsolateToken rootIsolateToken = RootIsolateToken.instance!;
Isolate.spawn(_isolateMain, rootIsolateToken);
}
```

### Executing channel handlers on background threads

In order for a channel's platform side handler to
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