save sensor data as json file

lib/light_sensor_event.dart

@@ -0,0 +1,11 @@
+import 'dart:ffi';
+
+class LightSensorEvent {
+  final double lux;
+  final int timestamp;
+  LightSensorEvent(this.lux, this.timestamp);
+  Map<String, dynamic> toJson() => {
+        'lux': lux,
+        'timestamp': timestamp,
+      };
+}

lib/main.dart

@@ -1,5 +1,10 @@
+import 'dart:convert';
+import 'dart:io';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import 'package:light_sesnor_capture/light_sensor_event.dart';
+import 'package:intl/intl.dart';
 
 void main() {
   runApp(const MyApp());
@@ -56,18 +61,10 @@ class MyHomePage extends StatefulWidget {
 }
 
 class _MyHomePageState extends State<MyHomePage> {
-  int _counter = 0;
-
-  void _incrementCounter() {
-    setState(() {
-      // This call to setState tells the Flutter framework that something has
-      // changed in this State, which causes it to rerun the build method below
-      // so that the display can reflect the updated values. If we changed
-      // _counter without calling setState(), then the build method would not be
-      // called again, and so nothing would appear to happen.
-      _counter++;
-    });
-  }
+  int mState = 0;
+  static const MethodChannel methodChannel =
+      MethodChannel('tw.moonjuice.light_sensor.method');
+  List mLightSensorEvents = [];
 
   @override
   Widget build(BuildContext context) {
@@ -107,12 +104,15 @@ class _MyHomePageState extends State<MyHomePage> {
           mainAxisAlignment: MainAxisAlignment.center,
           children: <Widget>[
             Spacer(),
-            StreamBuilder<String>(
+            StreamBuilder<LightSensorEvent>(
                 stream: streamSensorEventFromNative(),
                 builder: (context, snapshot) {
                   if (snapshot.hasData) {
+                    if (mState == 1) {
+                      mLightSensorEvents.add(snapshot.data);
+                    }
                     return Text(
-                      'Sensor Data: ${snapshot.data}',
+                      'Sensor Data: ${jsonEncode(snapshot.data)}',
                       style: Theme.of(context).textTheme.headlineLarge,
                     );
                   } else {
@@ -125,10 +125,13 @@ class _MyHomePageState extends State<MyHomePage> {
               children: [
                 Spacer(),
                 ElevatedButton(
-                    onPressed: onPressed, child: Text('Start Record')),
+                  onPressed: (mState == 0) ? onPressed : null,
+                  child: Text('Start Record'),
+                ),
                 Spacer(),
                 ElevatedButton(
-                    onPressed: onPressed, child: Text('Stop Record')),
+                    onPressed: (mState == 1) ? onPressed : null,
+                    child: Text('Stop Record')),
                 Spacer(),
               ],
             ),
@@ -139,12 +142,28 @@ class _MyHomePageState extends State<MyHomePage> {
     );
   }
 
-  void onPressed() {}
+  Future<void> onPressed() async {
+    setState(() {
+      mState = ((mState == 0) ? 1 : 0);
+    });
+    if (mState == 0) {
+      final String downloadsPath =
+          await methodChannel.invokeMethod('getExternalDownloadsPath');
+      DateTime now = DateTime.now();
+      String formattedDate = DateFormat('yyyy-MM-dd_HH-mm-ss').format(now);
+      File file = File('$downloadsPath/$formattedDate.txt');
+      var sink = file.openWrite();
+      sink.write(jsonEncode(mLightSensorEvents));
+      await sink.flush();
+      await sink.close();
+      mLightSensorEvents.clear();
+    }
+  }
 
-  Stream<String> streamSensorEventFromNative() {
+  Stream<LightSensorEvent> streamSensorEventFromNative() {
     const eventChannel = EventChannel('tw.moonjuice.light_sensor.stream');
     return eventChannel
         .receiveBroadcastStream()
-        .map((event) => event.toString());
+        .map((event) => LightSensorEvent(event['lux'], event['timestamp']));
   }
 }