通知消息控件

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  int _page = 0;
  @override
  Widget build(BuildContext context) {
    const bgColor = [Colors.red,Colors.green,Colors.yellow];
    bool isCheck = true;
    return MaterialApp(
        home: HomePage()
    );
  }

}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int num = 1;
  double _left = 0;
  double _top = 0;
  double _maxWidth = 0;
  double _maxHeight = 0;
  double _width = 300;
  double _height = 200;
  TextEditingController _controll=TextEditingController();
  GlobalKey _gKey = GlobalKey();
  @override
  void initState() {
    super.initState();
    
    WidgetsBinding.instance.addPostFrameCallback((_){
      print("addPostFrameCallback");
      _maxWidth = _gKey.currentContext.size.width;
      _maxHeight = _gKey.currentContext.size.height;
    });
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('LOL',style: TextStyle(color: Colors.yellow),),
      ),
      body: Builder(
        builder: (ctx) {
          return Center(
            child: RaisedButton(
              child: Text("按钮",
              ),
              onPressed: () {
                Scaffold.of(ctx).showSnackBar(SnackBar(
                  content: Text("你有未读消息！"),
                  duration: Duration(seconds: 3),
                  action: SnackBarAction(
                    label: "忽略",
                    onPressed: (){
                      print("点击了按钮");
                    },
                  ),
                ));
              },
            ),
          );
        }
      ),
    );
  }

}