在使用NgRx Store时，可以通过使用纯函数和高阶函数来避免使用if语句。下面是一种解决方法的示例代码：

1. 创建一个actions.ts文件，定义所有可能的action类型。

export enum ActionTypes {
  Increment = '[Counter] Increment',
  Decrement = '[Counter] Decrement',
  Reset = '[Counter] Reset'
}

export class Increment implements Action {
  readonly type = ActionTypes.Increment;
}

export class Decrement implements Action {
  readonly type = ActionTypes.Decrement;
}

export class Reset implements Action {
  readonly type = ActionTypes.Reset;
}

export type CounterActions = Increment | Decrement | Reset;

2. 创建一个reducer.ts文件，定义reducer函数。

import { CounterActions, ActionTypes } from './actions';

export interface CounterState {
  count: number;
}

export const initialState: CounterState = {
  count: 0
};

export function counterReducer(state = initialState, action: CounterActions): CounterState {
  switch (action.type) {
    case ActionTypes.Increment:
      return { ...state, count: state.count + 1 };
    case ActionTypes.Decrement:
      return { ...state, count: state.count - 1 };
    case ActionTypes.Reset:
      return { ...state, count: 0 };
    default:
      return state;
  }
}

3. 创建一个selectors.ts文件，定义selectors函数。

import { createSelector, createFeatureSelector } from '@ngrx/store';
import { CounterState } from './reducer';

export const selectCounterState = createFeatureSelector('counter');

export const selectCount = createSelector(
  selectCounterState,
  (state: CounterState) => state.count
);

4. 在组件中使用selectors和dispatch来获取和更新状态。

import { Component } from '@angular/core';
import { Store } from '@ngrx/store';
import { Increment, Decrement, Reset } from './actions';
import { selectCount } from './selectors';

@Component({
  selector: 'app-counter',
  template: `
    

      Increment
      {{ count$ | async }}
      Decrement
      Reset
    
  `
})
export class CounterComponent {
  count$ = this.store.select(selectCount);

  constructor(private store: Store) {}

  increment() {
    this.store.dispatch(new Increment());
  }

  decrement() {
    this.store.dispatch(new Decrement());
  }

  reset() {
    this.store.dispatch(new Reset());
  }
}

通过使用NgRx的action、reducer和selector，可以避免使用if语句来处理状态的变化，从而提高代码的可维护性和可测试性。