下面是一个使用Angular 6和@ngrx/store进行api调用的示例代码：

1. 首先，安装@ngrx/store和rxjs依赖项。

npm install @ngrx/store rxjs --save

2. 创建一个名为api.actions.ts的文件并定义一个action。

import { createAction, props } from '@ngrx/store';

export const loadItems = createAction('[API] Load Items');
export const loadItemsSuccess = createAction('[API] Load Items Success', props<{ data: any }>());
export const loadItemsFailure = createAction('[API] Load Items Failure', props<{ error: any }>());

3. 创建一个名为api.reducer.ts的文件并定义一个reducer。

import { createReducer, on } from '@ngrx/store';
import { loadItems, loadItemsSuccess, loadItemsFailure } from './api.actions';

export interface ApiState {
  loading: boolean;
  data: any;
  error: any;
}

export const initialState: ApiState = {
  loading: false,
  data: null,
  error: null
};

export const apiReducer = createReducer(
  initialState,
  on(loadItems, state => ({ ...state, loading: true })),
  on(loadItemsSuccess, (state, { data }) => ({ ...state, loading: false, data })),
  on(loadItemsFailure, (state, { error }) => ({ ...state, loading: false, error }))
);

4. 创建一个名为api.effects.ts的文件并定义一个effect。

import { Injectable } from '@angular/core';
import { Actions, createEffect, ofType } from '@ngrx/effects';
import { of } from 'rxjs';
import { map, mergeMap, catchError } from 'rxjs/operators';
import { ApiService } from './api.service';
import { loadItems, loadItemsSuccess, loadItemsFailure } from './api.actions';

@Injectable()
export class ApiEffects {
  loadItems$ = createEffect(() =>
    this.actions$.pipe(
      ofType(loadItems),
      mergeMap(() =>
        this.apiService.getItems().pipe(
          map(data => loadItemsSuccess({ data })),
          catchError(error => of(loadItemsFailure({ error })))
        )
      )
    )
  );

  constructor(private actions$: Actions, private apiService: ApiService) {}
}

5. 创建一个名为api.service.ts的文件并定义一个service。

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class ApiService {
  constructor(private http: HttpClient) {}

  getItems(): Observable {
    return this.http.get('https://example.com/api/items');
  }
}

6. 在你的模块中引入StoreModule和EffectsModule。

import { StoreModule } from '@ngrx/store';
import { EffectsModule } from '@ngrx/effects';
import { apiReducer } from './api.reducer';
import { ApiEffects } from './api.effects';

@NgModule({
  imports: [
    StoreModule.forRoot({ api: apiReducer }),
    EffectsModule.forRoot([ApiEffects])
  ],
  // ...
})
export class AppModule {}

7. 在你的组件中，使用store.dispatch()来分发action。

import { Component } from '@angular/core';
import { Store } from '@ngrx/store';
import { loadItems } from './api.actions';

@Component({
  selector: 'app-root',
  template: `
    Load Items
    
Loading...
    
{{ data | json }}
    
{{ error }}
  `
})
export class AppComponent {
  loading$ = this.store.select(state => state.api.loading);
  data$ = this.store.select(state => state.api.data);
  error$ = this.store.select(state => state.api.error);

  constructor(private store: Store) {}

  loadItems() {
    this.store.dispatch(loadItems());
  }
}

这是一个简单的示例，展示了如何在Angular 6中使用@ngrx/store和api调用。你可以根据你的需求对代码进行调整和扩展。