feat(add city picker demo):

lib/widgets/components/Pick/CityPIcker/demo.dart

@@ -8,14 +8,37 @@
 //
 
 import 'package:flutter/material.dart';
+import 'package:city_pickers/city_pickers.dart';
 
-class Demo extends StatefulWidget {
+class CityPickerDemo extends StatefulWidget {
   _Demo createState() => _Demo();
 }
 
-class _Demo extends State<Demo> {
+class _Demo extends State<CityPickerDemo> {
+  String _result;
+  show(context) async {
+    Result temp  = await CityPickers.showCityPicker(
+      context: context,
+//      locationCode: '640221',
+      height: 400,
+    );
+    setState(() {
+      _result = "${temp.toString()}";
+    });
+  }
 
   Widget build(BuildContext context) {
-    return Container();
+    return Center(
+        child: Column(
+          children: <Widget>[
+            Text("result: ${_result.toString()}"),
+            RaisedButton(
+              onPressed: () {this.show(context);
+              },
+              child: Text("select"),
+            ),
+          ],
+        )
+    );
   }
 }