Added scanDataStream & simplified Widget creation

- the QrViewController has a getter that returns a Stream of data that gets updated on every scan result
  - theres no need to init the QrViewController through a method, because the GlobalKey is generated inside the QrViewWidget
  - a dispose method was added to correctly dispose the stream

example/lib/main.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
 import 'package:qr_code_scanner/qr_code_scanner.dart';
 
 void main() => runApp(MaterialApp(home: QRViewExample()));
@@ -19,7 +18,6 @@ class QRViewExample extends StatefulWidget {
 }
 
 class _QRViewExampleState extends State<QRViewExample> {
-  final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
   var qrText = "";
   var flashState = flash_on;
   var cameraState = front_camera;
@@ -32,7 +30,6 @@ class _QRViewExampleState extends State<QRViewExample> {
         children: <Widget>[
           Expanded(
             child: QRView(
-              key: qrKey,
               onQRViewCreated: _onQRViewCreated,
             ),
             flex: 4,
@@ -128,17 +125,17 @@ class _QRViewExampleState extends State<QRViewExample> {
   }
 
   void _onQRViewCreated(QRViewController controller) {
-    final channel = controller.channel;
-    controller.init(qrKey);
     this.controller = controller;
-    channel.setMethodCallHandler((MethodCall call) async {
-      switch (call.method) {
-        case "onRecognizeQR":
-          dynamic arguments = call.arguments;
-          setState(() {
-            qrText = arguments.toString();
-          });
-      }
+    controller.scannedData.listen((scanData) {
+      setState(() {
+        qrText = scanData;
+      });
     });
   }
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
 }

lib/qr_code_scanner.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -17,6 +19,7 @@ class QRView extends StatefulWidget {
 }
 
 class _QRViewState extends State<QRView> {
+  final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
   @override
   Widget build(BuildContext context) {
     var androidView = AndroidView(
@@ -45,7 +48,7 @@ class _QRViewState extends State<QRView> {
     if (widget.onQRViewCreated == null) {
       return;
     }
-    widget.onQRViewCreated(new QRViewController._(id));
+    widget.onQRViewCreated(QRViewController._(id, qrKey));
   }
 }
 
@@ -71,18 +74,33 @@ class _CreationParams {
 }
 
 class QRViewController {
-  QRViewController._(int id)
-      : channel = MethodChannel('net.touchcapture.qr.flutterqr/qrview_$id');
-  final MethodChannel channel;
+  static const scanMethodCall = "onRecognizeQR";
+
+  StreamController<String> _scanUpdateController = StreamController<String>();
 
-  void init(GlobalKey qrKey) {
+  Stream<String> get scannedData => _scanUpdateController.stream;
+
+  QRViewController._(int id, GlobalKey qrKey)
+      : channel = MethodChannel('net.touchcapture.qr.flutterqr/qrview_$id') {
     if (defaultTargetPlatform == TargetPlatform.iOS) {
       final RenderBox renderBox = qrKey.currentContext.findRenderObject();
       channel.invokeMethod("setDimensions",
           {"width": renderBox.size.width, "height": renderBox.size.height});
     }
+    channel.setMethodCallHandler(
+      (MethodCall call) async {
+        switch (call.method) {
+          case scanMethodCall:
+            if (call.arguments != null) {
+              _scanUpdateController.sink.add(call.arguments.toString());
+            }
+        }
+      },
+    );
   }
 
+  final MethodChannel channel;
+
   void flipCamera() {
     channel.invokeMethod("flipCamera");
   }
@@ -98,4 +116,8 @@ class QRViewController {
   void resumeCamera() {
     channel.invokeMethod("resumeCamera");
   }
+
+  void dispose() {
+    _scanUpdateController.close();
+  }
 }