在视图层的使用 WillPopScope 做根组件

import 'package:flutter/material.dart';
class HomeView extends GetView<HomeController> {
    HomeView({Key? key}) : super(key: key);
    @override
  	Widget build(BuildContext context) {
        return Obx(（）{
            return WillPopScope(
            	onWillPop: ()async{
                    /* 判断两秒内点击两次返回按钮则退出APP */
                    if(controller.lastPopTime.value == null || DateTime.now().difference(controller.lastPopTime.value) > Duration(seconds: 2)){
                        Fluttertoast.showToast(
                            msg: "在按一次退出应用",
                            toastLength: Toast.LENGTH_SHORT,
                            gravity: ToastGravity.CENTER,
                            timeInSecForIosWeb: 1,
                            backgroundColor: Color.fromARGB(57, 0, 0, 0),
                            textColor: Colors.white,
                            fontSize: 16.0
                        );
                        controller.setLastPopTime();
                    }else{
                        /* 退出app */
                        await SystemChannels.platform.invokeMethod('SystemNavigator.pop');
                    }
                    return false;
                },
                child:Scaffold(...)
            )
        })
    }
}

在 controller 组件中设置时间

/* 监听再按一次退出APP */
var lastPopTime = DateTime.now().obs;
/* 确认退出APP */ 
setLastPopTime(){
    lastPopTime.value = DateTime.now();
    update();
}