如何在flutter中应用页面内容内的条件

Question

我试图在用户登录时在小部件上应用条件，显示小部件注销，否则显示登录按钮。这怎么可能？

登录前

登录后

<图片src="https://i.sstatic.net/BaTVD.png" alt="在此处输入图像描述">

我使用 shred_preferences 包保存、获取和删除使用过的数据。 这是我的代码：

shared_preferences

import 'package:shared_preferences/shared_preferences.dart';


class PrefServices{
  Future createCache(String username, String password) async {
    SharedPreferences _preferences = await SharedPreferences.getInstance();
    _preferences.setString("username", username);
    _preferences.setString("password", password);
  }

  Future readCache(String username) async {
    SharedPreferences _preferences = await SharedPreferences.getInstance();
    var username = _preferences.getString("username")?? "null";
    // _preferences.getString("password");
    return username;
  }

  Future<void> removeCache(String username, String password) async {
    SharedPreferences _preferences = await SharedPreferences.getInstance();
    _preferences.remove("username");
    _preferences.remove("password");
  }


}

配置文件屏幕

import 'dart:async';
import 'package:clothing_roll/shred_preferences/shred_preferences_services.dart';
import 'package:clothing_roll/ui/widget/profile/login_widget.dart';
import 'package:clothing_roll/ui/widget/profile/profiles_widget.dart';
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';


class ProfileScreen extends StatefulWidget {
  const ProfileScreen({ Key? key }) : super(key: key);

  @override
  _ProfileScreen createState() => _ProfileScreen();
}

class _ProfileScreen extends State<ProfileScreen> {

  final PrefServices _prefServices = PrefServices();

  @override
  void initState() {
    _prefServices.readCache("username").then((value) {
      print(value.toString());
      if (value != null) {
        return Timer(Duration(seconds: 1),
            () => ProfileWidget());
      } else {
        return Timer(Duration(seconds: 1),
            () => LoginWidget());
      }
    });
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

Answer 1

注意：我使用了 Getx 包

1. 创建一个 bool 变量用于条件检查，
2. 将三元运算符添加到 bool 变量并更改条件

class Test1 extends StatelessWidget {
  Controller controller = Get.put(Controller());

  Test1({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Container(
        width: Get.width,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            ElevatedButton(
                onPressed: () {
                  controller.isLogged.value = !controller.isLogged.value;
                },
                child: Text("Press to change value")),
            Obx(
              () => controller.isLogged.value
                  ? ElevatedButton(onPressed: () {}, child: Text("logged In"))
                  : ElevatedButton(onPressed: () {}, child: Text("Logged Out")),
            ),
          ],
        ),
      ),
    );
  }
}