如何从控制器层获取 devicePixelRatio？ - 颤振

问题描述

我是 flutter 的初学者，现在正在学习 MVC 模式，我正在使用 GetX 进行状态管理。

我需要为 devicePixelRatio 参数传递一个 double 类型的值，如下图所示。

Image 1

但是，我无法在控制器中恢复此值，因为我没有“上下文”

Image 2

是否可以在控制器中获取此值？或者通过视图层传递这个值？

我正在寻找解决方案，但我没有找到答案，如果有人可以提供帮助，在此先感谢您。

解决方法

您可以在下面复制粘贴运行完整代码
我用官方的例子来模拟这种情况
您可以使用 double pixelRatio = Get.context.devicePixelRatio;
代码片段

class Controller extends GetxController {
  double pixelRatio = Get.context.devicePixelRatio;

  int count = 0;
  void increment() {
    print("pixelRatio $pixelRatio");
    count++;
    // use update method to update all count variables
    update();
  }
}

点击浮动动作按钮时输出

I/flutter (19594): pixelRatio 3.5

完整代码

import 'package:flutter/material.dart';
import 'package:get/get.dart';

void main() {
  runApp(GetMaterialApp(
    // It is not mandatory to use named routes,but dynamic urls are interesting.
    initialRoute: '/home',defaultTransition: Transition.native,translations: MyTranslations(),locale: Locale('pt','BR'),getPages: [
      //Simple GetPage
      GetPage(name: '/home',page: () => First()),// GetPage with custom transitions and bindings
      GetPage(
        name: '/second',page: () => Second(),customTransition: SizeTransitions(),binding: SampleBind(),),// GetPage with default transitions
      GetPage(
        name: '/third',transition: Transition.cupertino,page: () => Third(),],));
}

class MyTranslations extends Translations {
  @override
  Map<String,Map<String,String>> get keys => {
        'en': {
          'title': 'Hello World %s',},'en_US': {
          'title': 'Hello World from US','pt': {
          'title': 'Olá de Portugal','pt_BR': {
          'title': 'Olá do Brasil',};
}

class Controller extends GetxController {
  double pixelRatio = Get.context.devicePixelRatio;

  int count = 0;
  void increment() {
    print("pixelRatio $pixelRatio");
    count++;
    // use update method to update all count variables
    update();
  }
}

class First extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          icon: Icon(Icons.add),onPressed: () {
            Get.snackbar("Hi","I'm modern snackbar");
          },title: Text("title".trArgs(['John'])),body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,children: [
            GetBuilder<Controller>(
                init: Controller(),// You can initialize your controller here the first time. Don't use init in your other GetBuilders of same controller
                builder: (_) => Text(
                      'clicks: ${_.count}',)),RaisedButton(
              child: Text('Next Route'),onPressed: () {
                Get.toNamed('/second');
              },RaisedButton(
              child: Text('Change locale to English'),onPressed: () {
                Get.updateLocale(Locale('en','UK'));
              },floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add),onPressed: () {
            Get.find<Controller>().increment();
          }),);
  }
}

class Second extends GetView<ControllerX> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('second Route'),children: [
            GetX<ControllerX>(
              // Using bindings you don't need of init: method
              // Using Getx you can take controller instance of "builder: (_)"
              builder: (_) {
                print("count1 rebuild");
                return Text('${_.count1}');
              },GetX<ControllerX>(
              builder: (_) {
                print("count2 rebuild");
                return Text('${controller.count2}');
              },GetX<ControllerX>(builder: (_) {
              print("sum rebuild");
              return Text('${_.sum}');
            }),GetX<ControllerX>(
              builder: (_) => Text('Name: ${controller.user.value.name}'),GetX<ControllerX>(
              builder: (_) => Text('Age: ${_.user.value.age}'),RaisedButton(
              child: Text("Go to last page"),onPressed: () {
                Get.toNamed('/third',arguments: 'arguments of second');
              },RaisedButton(
              child: Text("Back page and open snackbar"),onPressed: () {
                Get.back();
                Get.snackbar(
                  'User 123','Successfully created',);
              },RaisedButton(
              child: Text("Increment"),onPressed: () {
                Get.find<ControllerX>().increment();
              },onPressed: () {
                Get.find<ControllerX>().increment2();
              },RaisedButton(
              child: Text("Update name"),onPressed: () {
                Get.find<ControllerX>().updateUser();
              },RaisedButton(
              child: Text("Dispose worker"),onPressed: () {
                Get.find<ControllerX>().disposeWorker();
              },);
  }
}

class Third extends GetView<ControllerX> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(onPressed: () {
        controller.incrementList();
      }),appBar: AppBar(
        title: Text("Third ${Get.arguments}"),body: Center(
          child: Obx(() => ListView.builder(
              itemCount: controller.list.length,itemBuilder: (context,index) {
                return Text("${controller.list[index]}");
              }))),);
  }
}

class SampleBind extends Bindings {
  @override
  void dependencies() {
    Get.lazyPut<ControllerX>(() => ControllerX());
  }
}

class User {
  User({this.name = 'Name',this.age = 0});
  String name;
  int age;
}

class ControllerX extends GetxController {
  final count1 = 0.obs;
  final count2 = 0.obs;
  final list = [56].obs;
  final user = User().obs;

  updateUser() {
    user.update((value) {
      value.name = 'Jose';
      value.age = 30;
    });
  }

  /// Once the controller has entered memory,onInit will be called.
  /// It is preferable to use onInit instead of class constructors or initState method.
  /// Use onInit to trigger initial events like API searches,listeners registration
  /// or Workers registration.
  /// Workers are event handlers,they do not modify the final result,/// but it allows you to listen to an event and trigger customized actions.
  /// Here is an outline of how you can use them:

  /// made this if you need cancel you worker
  Worker _ever;

  @override
  onInit() {
    /// Called every time the variable $_ is changed
    _ever = ever(count1,(_) => print("$_ has been changed (ever)"));

    everAll([count1,count2],(_) => print("$_ has been changed (everAll)"));

    /// Called first time the variable $_ is changed
    once(count1,(_) => print("$_ was changed once (once)"));

    /// Anti DDos - Called every time the user stops typing for 1 second,for example.
    debounce(count1,(_) => print("debouce$_ (debounce)"),time: Duration(seconds: 1));

    /// Ignore all changes within 1 second.
    interval(count1,(_) => print("interval $_ (interval)"),time: Duration(seconds: 1));
  }

  int get sum => count1.value + count2.value;

  increment() => count1.value++;

  increment2() => count2.value++;

  disposeWorker() {
    _ever.dispose();
    // or _ever();
  }

  incrementList() => list.add(75);
}

class SizeTransitions extends CustomTransition {
  @override
  Widget buildTransition(
      BuildContext context,Curve curve,Alignment alignment,Animation<double> animation,Animation<double> secondaryAnimation,Widget child) {
    return Align(
      alignment: Alignment.center,child: SizeTransition(
        sizeFactor: CurvedAnimation(
          parent: animation,curve: curve,child: child,);
  }
}