Update example REAMD.md code to reflect api changes

The example is copied verbatim from ./example/lib/main.dart

example/README.md

@@ -22,11 +22,15 @@ Demonstrates how to use the qr_code_scanner plugin.
 ## Example:
 ```dart
 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()));
 
+const flashOn = 'FLASH ON';
+const flashOff = 'FLASH OFF';
+const frontCamera = 'FRONT CAMERA';
+const backCamera = 'BACK CAMERA';
+
 class QRViewExample extends StatefulWidget {
   const QRViewExample({
     Key key,
@@ -37,60 +41,144 @@ class QRViewExample extends StatefulWidget {
 }
 
 class _QRViewExampleState extends State<QRViewExample> {
-  final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
-  var qrText = "";
+  var qrText = '';
+  var flashState = flashOn;
+  var cameraState = frontCamera;
   QRViewController controller;
+  final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       body: Column(
         children: <Widget>[
           Expanded(
+            flex: 4,
             child: QRView(
               key: qrKey,
               onQRViewCreated: _onQRViewCreated,
+              overlay: QrScannerOverlayShape(
+                borderColor: Colors.red,
+                borderRadius: 10,
+                borderLength: 30,
+                borderWidth: 10,
+                cutOutSize: 300,
+              ),
             ),
-            flex: 4,
           ),
           Expanded(
-            child: Column(children:
-              <Widget>[
-                Text("This is the result of scan: $qrText"),
-                RaisedButton(
-                  onPressed: (){
-                    if(controller != null){
-                      controller.flipCamera();
-                    }
-                  },
-                  child: Text(
-                      'Flip',
-                      style: TextStyle(fontSize: 20)
+            flex: 1,
+            child: FittedBox(
+              fit: BoxFit.contain,
+              child: Column(
+                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+                children: <Widget>[
+                  Text('This is the result of scan: $qrText'),
+                  Row(
+                    mainAxisAlignment: MainAxisAlignment.center,
+                    crossAxisAlignment: CrossAxisAlignment.center,
+                    children: <Widget>[
+                      Container(
+                        margin: EdgeInsets.all(8),
+                        child: RaisedButton(
+                          onPressed: () {
+                            if (controller != null) {
+                              controller.toggleFlash();
+                              if (_isFlashOn(flashState)) {
+                                setState(() {
+                                  flashState = flashOff;
+                                });
+                              } else {
+                                setState(() {
+                                  flashState = flashOn;
+                                });
+                              }
+                            }
+                          },
+                          child:
+                              Text(flashState, style: TextStyle(fontSize: 20)),
+                        ),
+                      ),
+                      Container(
+                        margin: EdgeInsets.all(8),
+                        child: RaisedButton(
+                          onPressed: () {
+                            if (controller != null) {
+                              controller.flipCamera();
+                              if (_isBackCamera(cameraState)) {
+                                setState(() {
+                                  cameraState = frontCamera;
+                                });
+                              } else {
+                                setState(() {
+                                  cameraState = backCamera;
+                                });
+                              }
+                            }
+                          },
+                          child:
+                              Text(cameraState, style: TextStyle(fontSize: 20)),
+                        ),
+                      )
+                    ],
                   ),
-                )
-              ],
+                  Row(
+                    mainAxisAlignment: MainAxisAlignment.center,
+                    crossAxisAlignment: CrossAxisAlignment.center,
+                    children: <Widget>[
+                      Container(
+                        margin: EdgeInsets.all(8),
+                        child: RaisedButton(
+                          onPressed: () {
+                            controller?.pauseCamera();
+                          },
+                          child: Text('pause', style: TextStyle(fontSize: 20)),
+                        ),
+                      ),
+                      Container(
+                        margin: EdgeInsets.all(8),
+                        child: RaisedButton(
+                          onPressed: () {
+                            controller?.resumeCamera();
+                          },
+                          child: Text('resume', style: TextStyle(fontSize: 20)),
+                        ),
+                      )
+                    ],
+                  ),
+                ],
+              ),
             ),
-            flex: 1,
           )
         ],
       ),
     );
   }
 
+  bool _isFlashOn(String current) {
+    return flashOn == current;
+  }
+
+  bool _isBackCamera(String current) {
+    return backCamera == current;
+  }
+
   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.scannedDataStream.listen((scanData) {
+      setState(() {
+        qrText = scanData;
+      });
     });
   }
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
 }
+
 ```