Capitulo 11 ➜ Notificaciones

¿Cómo implementar notificaciones para un carrito de compra?

Para implementamos variables globales para el snackbar

  final GlobalKey<ScaffoldState> _globalKey = new GlobalKey<ScaffoldState>();

...
 child: Scaffold(
          key: _globalKey,
          backgroundColor: Colors.amber,
....

Implementación de actions en AppBar

appBar: AppBar(
            title: Text("CARTA"),
            backgroundColor: Colors.amber,
            elevation: 0,
            bottom: TabBar(
              labelColor: Colors.red,
              indicatorColor: Colors.red,
              indicatorSize: TabBarIndicatorSize.label,
              tabs: <Widget>[
                new Tab(
                  child: Padding(
                    padding: EdgeInsets.only(left: 5, right: 5),
                    child: Text("PLATOS"),
                  ),
                ),
                new Tab(
                  child: Padding(
                    padding: EdgeInsets.only(left: 5, right: 5),
                    child: Text("BEBIDAS"),
                  ),
                ),
                new Tab(
                  child: Padding(
                    padding: EdgeInsets.only(left: 5, right: 5),
                    child: Text("POSTRES"),
                  ),
                )
              ],
            ),
            actions: <Widget>[
              new Stack(
                children: <Widget>[
                  IconButton(
                      icon: Icon(Icons.shopping_cart),
                      onPressed: () {
                        carrito.numeroItems!=0 ?
                        Navigator.of(context).push(MaterialPageRoute(
                          builder: (BuildContext) => PantallaCarrito()
                        ))
                            :
                        _globalKey.currentState.showSnackBar(SnackBar(
                          content: Text("Llenar el carrito", textAlign: TextAlign.center,),
                        ));

                      }
                      ),
                  new Positioned(
                      top: 6,
                      right: 6,
                      child: Container(
                        padding: EdgeInsets.all(2),
                        decoration: new BoxDecoration(
                            color: Colors.red,
                            borderRadius: BorderRadius.circular(4)),
                        constraints: BoxConstraints(
                          minWidth: 14,
                          minHeight: 14
                        ),
                        child: Text(
                          carrito.numeroItems.toString(),
                          textAlign: TextAlign.center,
                          style: TextStyle(
                          color: Colors.white,
                          fontSize: 10
                        ),),
                      )
                  )
                ],
              )
            ],
          ),