我使用自定义中间件 ( meta-reducer ) 打印我的 ngrx-store
每次调度一个 Action 。我直接在 app.module.ts
里面写了我的中间件(我还应该把它放在哪里?):
app.module.ts
// ...imports
// ...
// FIXME:
/**
* console.log action and state(before action) each time an action is dipatched
* @param reducer reducer
*/
export function debug(reducer: ActionReducer<AppState, Actions>): ActionReducer<AppState, Actions> {
const logger = new LoggerService(); ////////////// ERROR \\\\\\\\\\\\\\
return (state, action) => {
logger.storeInfo('ACTION', action);
logger.storeInfo('STATE', state);
return reducer(state, action);
};
}
export const metaReducers: MetaReducer<any>[] = [
debug,
];
@NgModule({
declarations: [AppComponent, LoggerServiceComponent],
entryComponents: [],
imports: [
// ...
StoreModule.forRoot(reducers, { metaReducers }),
StoreRouterConnectingModule.forRoot(), // Connects RouterModule with StoreModule
],
providers: [
// ...
],
bootstrap: [AppComponent],
})
export class AppModule {}
有一个错误,因为我的
LoggerService
注入(inject)了一个存储(因为我希望我的所有日志都存储在 ngx-store
中。 但我也无法访问存储!。此外,我确信这不是访问服务的单例实例...SomeClass.getServiceInstance(type)
? [编辑 1] - 使用
META_REDUCERS
(第一次尝试 - 失败)app.module.ts
import { LoggerService } from './services/logger.service';
import { AppState, Actions } from './app.state';
import { StoreModule, MetaReducer, ActionReducer, META_REDUCERS } from '@ngrx/store';
/**
* Injects a `LoggerService` inside a `MetaReducer`
* @param logger a service that allows to log and store console.log() messages
* @returns a `MetaReducer`
*/
function debugFactory(logger: LoggerService): MetaReducer<AppState> {
return (reducer: ActionReducer<AppState, Actions>): ActionReducer<AppState, Actions> => {
return (state, action) => {
logger.storeInfo('ACTION', action);
logger.storeInfo('STATE', state);
return reducer(state, action);
};
};
}
/**
* Injects a LoggerService inside the debug `MetaReducer` function
* @param logger a service that allows to log and store console.log() messages
* @returns A list of `MetaReducer`
*/
export function getMetaReducers(logger: LoggerService): MetaReducer<AppState>[] {
return [debugFactory(logger)];
}
const reducers = {
layout: layoutReducer,
preferences: preferencesReducer,
router: routerReducer,
debug: debugReducer,
};
@NgModule({
declarations: [AppComponent ],
entryComponents: [],
imports: [
// ...
StoreModule.forRoot(reducers),
StoreRouterConnectingModule.forRoot(), // Connects RouterModule with StoreModule
],
providers: [
// ...
{
provide: META_REDUCERS,
deps: [LoggerService],
useFactory: getMetaReducers,
multi: true,
},
],
bootstrap: [AppComponent],
})
export class AppModule {}
根据文档,这应该可以工作,但在运行时出现以下错误:
TypeError: "fn is not a function"
对应这个函数(在 njrx-store 库中):
/**
* @param {...?} functions
* @return {?}
*/
function compose(...functions) {
return (/**
* @param {?} arg
* @return {?}
*/
function (arg) {
if (functions.length === 0) {
return arg;
}
/** @type {?} */
const last = functions[functions.length - 1];
/** @type {?} */
const rest = functions.slice(0, -1);
return rest.reduceRight((/**
* @param {?} composed
* @param {?} fn
* @return {?}
*/
(composed, fn) => {
return fn(composed) // <----- HERE
}), last(arg));
});
}
在调试器中,它显示函数数组(
...functions
)包含一些函数和一个数组,我怀疑这是 getMetaReducers
方法的结果.我怀疑示例是错误的,或者 compose
的实现存在问题方法。如果您在我的代码中看到任何错误的内容,请告诉我。
[编辑 2] - 使用
USER_PROVIDED_META_REDUCERS
如答案中所述(第二次尝试 - 失败)已编辑的代码
// OLD
providers: [
// ...
{
provide: META_REDUCERS,
deps: [LoggerService],
useFactory: getMetaReducers,
multi: true,
},
],
// NEW
providers: [
// ...
{
provide: USER_PROVIDED_META_REDUCERS,
deps: [LoggerService],
useFactory: getMetaReducers,
},
],
看来我的
LoggerService
没有正确传递也没有初始化,因为我现在有这个错误:core.js:9110 ERROR TypeError: Cannot read property 'storeInfo' of undefined
at http://localhost:8102/main.js:636:20
at http://localhost:8102/vendor.js:109798:20
at computeNextEntry (http://localhost:8102/vendor.js:108628:21)
at recomputeStates (http://localhost:8102/vendor.js:108681:15)
at http://localhost:8102/vendor.js:109029:26
at ScanSubscriber.StoreDevtools.liftedAction$.pipe.Object.state [as accumulator] (http://localhost:8102/vendor.js:109081:38)
at ScanSubscriber._tryNext (http://localhost:8102/vendor.js:120261:27)
at ScanSubscriber._next (http://localhost:8102/vendor.js:120254:25)
at ScanSubscriber.next (http://localhost:8102/vendor.js:114391:18)
at WithLatestFromSubscriber._next (http://localhost:8102/vendor.js:122330:34)
如果我评论这些行:
logger.storeInfo('ACTION', action);
logger.storeInfo('STATE', state);
不会抛出异常,但我的记录器也不会工作。
但是至少存储正确地配置了自己,现在的问题只是 LoggerService 没有正确传递或初始化。我想我还是做错了什么
最佳答案
您应该尝试使用 META_REDUCERS
注入(inject)元 reducer 。 token 为 documented :
( HEADS UP :截至 24.Sept 文档有点误导,工厂方法返回类型应为 MetaReducer
而不是 MetaReducer[]
。检查 this example in the codebase)
export debugFactory(logger: LoggerService): MetaReducer<AppState> {
return (reducer: ActionReducer<AppState, Actions>): ActionReducer<AppState, Actions> => {
return (state, action) => {
logger.storeInfo('ACTION', action);
logger.storeInfo('STATE', state);
return reducer(state, action);
};
}
}
@NgModule({
providers: [
{
provide: META_REDUCERS,
deps: [LoggerService],
useFactory: debugFactory,
multi: true
},
],
})
export class AppModule {}
更新:
Since v8您可以使用
ÙSER_PROVIDED_META_REDUCERS
token :export function getMetaReducers(logger: LoggerService): MetaReducer<AppState>[] {
return [debugFactory(logger)];
}
providers: [
{
provide: USER_PROVIDED_META_REDUCERS,
deps: [LoggerService],
useFactory: getMetaReducers
},
],
在这种情况下,提供的工厂方法必须返回
MetaReducer[]
. “库”和“用户”提供的元缩减器在 this function 中合并为一个集合.您很可能会遇到商店和记录器服务之间的循环依赖关系,因为在创建商店期间,Angular 的 IOC 容器将尝试在商店创建完成之前实例化依赖于商店的记录器服务.您可以通过将 Injector 注入(inject)其中并为存储定义 getter 属性“懒惰地”访问记录器服务中的存储来解决此问题,例如:
private get() store{return this.injector.get(Store);}
ctor(private readonly injector: Injector){}
关于angular - NgRx:如何在 meta-reducers 中使用服务?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58066622/