added: implemented shared_preferences plugin in persist_key_value example

persist_key_value/lib/main.dart

@@ -1,25 +1,101 @@
 import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 
 void main() {
+  runApp(new MaterialApp(
+      // Disable the debug flag
+      debugShowCheckedModeBanner: false,
+      // Home
+      home: new MyHome()));
+}
+
+class MyHome extends StatefulWidget {
+  @override
+  MyHomeState createState() {
+    return new MyHomeState();
+  }
+}
+
+class MyHomeState extends State<MyHome> {
   var nameOfApp = "Persist Key Value";
 
-  runApp(new MaterialApp(
-      // Title
-      title: nameOfApp,
-      // Home
-      home: new Scaffold(
-        // Appbar
-        appBar: new AppBar(
-          // Title
-          title: new Text(nameOfApp),
-        ),
-        // Body
-        body: new Container(
-          // Center the content
-          child: new Center(
-            // Add Text
-            child: new Text("Hello World!"),
+  var counter = 0;
+
+  // define a key to use later
+  var key = "counter";
+
+  @override
+  void initState() {
+    super.initState();
+    _loadSavedData();
+  }
+
+  _loadSavedData() async {
+    // Get shared preference instance
+    SharedPreferences prefs = await SharedPreferences.getInstance();
+    setState(() {
+      // Get value
+      counter = (prefs.getInt(key) ?? 0);
+    });
+  }
+
+  _onIncrementHit() async {
+    // Get shared preference instance
+    SharedPreferences prefs = await SharedPreferences.getInstance();
+
+    setState(() {
+      // Get value
+      counter = (prefs.getInt(key) ?? 0) + 1;
+    });
+
+    // Save Value
+    prefs.setInt(key, counter);
+  }
+
+  _onDecrementHit() async {
+    // Get shared preference instance
+    SharedPreferences prefs = await SharedPreferences.getInstance();
+
+    setState(() {
+      // Get value
+      counter = (prefs.getInt(key) ?? 0) - 1;
+    });
+
+    // Save Value
+    prefs.setInt(key, counter);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      // Appbar
+      appBar: new AppBar(
+        // Title
+        title: new Text(nameOfApp),
+      ),
+      // Body
+      body: new Container(
+        // Center the content
+        child: new Center(
+          child: new Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              new Text(
+                '$counter',
+                textScaleFactor: 10.0,
+              ),
+              new Padding(padding: new EdgeInsets.all(10.0)),
+              new RaisedButton(
+                  onPressed: _onIncrementHit,
+                  child: new Text('Increment Counter')),
+              new Padding(padding: new EdgeInsets.all(10.0)),
+              new RaisedButton(
+                  onPressed: _onDecrementHit,
+                  child: new Text('Decrement Counter')),
+            ],
           ),
         ),
-      )));
+      ),
+    );
+  }
 }