Angular No provider for EffectsRootModule错误消息

错误消息：

main.ts:12 NullInjectorError: R3InjectorError(AppModule)[EffectsFeatureModule -> EffectsRootModule -> EffectsRootModule -> EffectsRootModule]: NullInjectorError: No provider for EffectsRootModule! at NullInjector.get (http://localhost:4200/vendor.js:62758:27) at R3Injector.get (http://localhost:4200/vendor.js:76765:33) at R3Injector.get (http://localhost:4200/vendor.js:76765:33) at R3Injector.get (http://localhost:4200/vendor.js:76765:33) at injectInjectorOnly (http://localhost:4200/vendor.js:62613:33) at Module.ɵɵinject (http://localhost:4200/vendor.js:62623:57) at Object.EffectsFeatureModule_Factory [as factory] (http://localhost:4200/vendor.js:137576:239) at R3Injector.hydrate (http://localhost:4200/vendor.js:77003:63) at R3Injector.get (http://localhost:4200/vendor.js:76753:33) at http://localhost:4200/vendor.js:76799:25 (anonymous) @ main.ts:12 invoke @ zone-evergreen.js:364 run @ zone-evergreen.js:123 (anonymous) @ zone-evergreen.js:857 invokeTask @ zone-evergreen.js:399 runTask @ zone-evergreen.js:167 drainMicroTaskQueue @ zone-evergreen.js:569 Promise.then (async) scheduleMicroTask @ zone-evergreen.js:552 scheduleTask @ zone-evergreen.js:388 scheduleTask @ zone-evergreen.js:210 scheduleMicroTask @ zone-evergreen.js:230 scheduleResolveOrReject @ zone-evergreen.js:847 then @ zone-evergreen.js:979 bootstrapModule @ core.js:42679 ./src/main.ts @ main.ts:11 webpack_require @ bootstrap:79 0 @ unless.directive.ts:33 webpack_require @ bootstrap:79 checkDeferredModules @ bootstrap:45 webpackJsonpCallback @ bootstrap:32 (anonymous) @ main.js:1

应用程序自己开发的module：

EffectsFeatureModule是dependent type之一：

value是null，所以报错：

在app.module.ts里加上一行语句即可解决问题：

EffectsModule.forRoot([AppEffects]),

这个forRoot方法为EffectsRootModule提供了可用的provider：