snapshot of https://github.com/flutter/samples.git (main, 2026-09-16; blobs > 131072B omitted)

background_isolate_channels/lib/main.dart

@@ -0,0 +1,156 @@
+// Copyright 2022 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:io' show Directory;
+
+import 'package:flutter/material.dart';
+import 'package:intl/intl.dart';
+import 'package:path/path.dart' as path;
+import 'package:path_provider/path_provider.dart' as path_provider;
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:uuid/uuid.dart' as uuid;
+
+import 'simple_database.dart';
+
+///////////////////////////////////////////////////////////////////////////////
+// This is the UI which will present the contents of the [SimpleDatabase]. To
+// see where Background Isolate Channels are used see simple_database.dart.
+///////////////////////////////////////////////////////////////////////////////
+
+void main() {
+  runApp(const MyApp());
+}
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Background Isolate Channels',
+      theme: ThemeData(primarySwatch: Colors.blue),
+      home: const MyHomePage(title: 'Background Isolate Channels'),
+    );
+  }
+}
+
+class MyHomePage extends StatefulWidget {
+  const MyHomePage({super.key, required this.title});
+
+  final String title;
+
+  @override
+  State<MyHomePage> createState() {
+    return _MyHomePageState();
+  }
+}
+
+class _MyHomePageState extends State<MyHomePage> {
+  /// The database that is running on a background [Isolate]. This is nullable
+  /// because acquiring a [SimpleDatabase] is an asynchronous operation. This
+  /// value is `null` until the database is initialized.
+  SimpleDatabase? _database;
+
+  /// Local cache of the query results returned by the [SimpleDatabase] for the
+  /// UI to render from. It is nullable since querying the results is
+  /// asynchronous. The value is `null` before any result has been received.
+  List<String>? _entries;
+
+  /// What is searched for in the [SimpleDatabase].
+  String _query = '';
+
+  @override
+  void initState() {
+    // Write the value to [SharedPreferences] which will get read on the
+    // [SimpleDatabase]'s isolate. For this example the value is always true
+    // just for demonstration purposes.
+    final SharedPreferencesAsync sharedPreferences = SharedPreferencesAsync();
+
+    final Future<void> sharedPreferencesSet = sharedPreferences.setBool(
+      'isDebug',
+      true,
+    );
+    final Future<Directory> tempDirFuture = path_provider
+        .getTemporaryDirectory();
+
+    // Wait until the [SharedPreferences] value is set and the temporary
+    // directory is received before opening the database. If
+    // [sharedPreferencesSet] does not happen before opening the
+    // [SimpleDatabase] there has to be a way to refresh
+    // [_SimpleDatabaseServer]'s [SharedPreferences] cached values.
+    Future.wait([sharedPreferencesSet, tempDirFuture]).then((values) {
+      final Directory? tempDir = values[1] as Directory?;
+      final String dbPath = path.join(tempDir!.path, 'database.db');
+      SimpleDatabase.open(dbPath).then((database) {
+        setState(() {
+          _database = database;
+        });
+        _refresh();
+      });
+    });
+    super.initState();
+  }
+
+  @override
+  void dispose() {
+    _database?.stop();
+    super.dispose();
+  }
+
+  /// Performs a find on [SimpleDatabase] with [query] and updates the listed
+  /// contents.
+  void _refresh({String? query}) {
+    if (query != null) {
+      _query = query;
+    }
+    _database!.find(_query).toList().then((entries) {
+      setState(() {
+        _entries = entries;
+      });
+    });
+  }
+
+  /// Adds a UUID and a timestamp to the [SimpleDatabase].
+  void _addDate() {
+    final DateTime now = DateTime.now();
+    final DateFormat formatter = DateFormat(
+      'EEEE MMMM d, HH:mm:ss\n${const uuid.Uuid().v4()}',
+    );
+    final String formatted = formatter.format(now);
+    _database!.addEntry(formatted).then((_) => _refresh());
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(widget.title),
+        bottom: PreferredSize(
+          preferredSize: const Size.fromHeight(kToolbarHeight),
+          child: Padding(
+            padding: const EdgeInsets.symmetric(horizontal: 8.0),
+            child: SearchBar(
+              hintText: 'Search',
+              onChanged: _database == null
+                  ? null
+                  : (query) => _refresh(query: query),
+              trailing: const [Icon(Icons.search), SizedBox(width: 8)],
+            ),
+          ),
+        ),
+      ),
+      body: ListView.builder(
+        itemBuilder: (context, index) {
+          return ListTile(title: Text(_entries![index]));
+        },
+        itemCount: _entries?.length ?? 0,
+      ),
+      floatingActionButton: FloatingActionButton(
+        onPressed: _database == null ? null : _addDate,
+        tooltip: 'Add',
+        child: const Icon(Icons.add),
+      ),
+    );
+  }
+}