iOS端Flutter使用Workmanager模拟后台拉取访问SharedPreferences报MissingPluginException

问题根因 #

你遇到的MissingPluginException是因为Workmanager触发的后台任务运行在独立的Dart Isolate中，该Isolate默认不会继承主Isolate的插件注册信息，所以SharedPreferences的原生通道实现没有被注册到后台Isolate中。另外你的AppDelegate.swift存在语法错误，嵌套了重复的AppDelegate类也会导致后台配置不生效。

Dart侧修改 #

调整callbackDispatcher方法的初始化逻辑，同时修正异步方法调用的等待逻辑：

void callbackDispatcher() {
  // 第一行添加，确保后台Isolate完成组件绑定和插件注册
  WidgetsFlutterBinding.ensureInitialized();
  print("callBackDispatcher");
  workmanager.executeTask((task, inputData) async {
    // 异步方法需要加await等待执行完成
    await setSwitches();
    return Future.value(true);
  });
}

iOS侧AppDelegate.swift修改 #

删除嵌套的冗余AppDelegate类，添加Workmanager插件注册回调，合并后台配置逻辑：

import UIKit
import Flutter
import workmanager

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    // 注册后台Isolate的插件回调
    WorkmanagerPlugin.setPluginRegistrantCallback { registry in
      GeneratedPluginRegistrant.register(with: registry)
    }
    UNUserNotificationCenter.current().delegate = self
    // 配置后台拉取间隔
    UIApplication.shared.setMinimumBackgroundFetchInterval(TimeInterval(60*15))
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }

  override func userNotificationCenter(_ center: UNUserNotificationCenter,
    willPresent notification: UNNotification,
    withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        completionHandler(.alert)
    }
}

生效验证 #

• 执行flutter clean清理项目缓存
• 执行flutter pub get重新拉取依赖
• 卸载测试设备上的旧安装包，重新编译运行即可

内容的提问来源于stack exchange，提问作者Kristin Vernon