Project Structure Overview

entry/src/main/ets/
|---ui-components
|   |---TabNav.ets                      // Bottom tab navigation panel
|   |---SpecSelector.ets                // Product specification selection
|   |---PromoDialog.ets                 // Promotional overlay
|   |---ProductInfo.ets                  // Detailed product specs block
|   |---PriceTag.ets                     // Price display component
|---dummy-data
|   |---ProductDetailData.ets            // Product detail mock data
|   |---ProductListData.ets              // Product catalog mock data
|---data-models
|   |---ProductDetail.ets                // Product detail type definitions
|   |---ProductItem.ets                  // Product item type definitions
|---screens
|   |---ProductDetail.ets               // Product detail screen
|   |---Home.ets                          // Main catalog screen
|   |---ShoppingCart.ets                   // Cart screen
|---cart-feature
|   |---CartPanel.ets                     // Cart content panel
|   |---RecommendedList.ets                  // Recommended product grid
|---helpers
|   |---LogHelper.ets                    // Log utility wrapper
feature/event-bus/src/main/ets/
|---constants
|   |---EventKeys.ts                       // Event ID constants
|---helpers
|   |---feature
|   |   |---EventBusManager.ets           // Custom event emitter wrapper

Custom Event Bus Implementation

import emitter from '@ohos.events.emitter';
import { EventKeys } from '../../constants/EventKeys';
import Base from '@ohos.base';

interface EventPayload {
  itemId: number;
}

interface EventWrapper {
  payload: EventPayload;
}

export class EventBusManager {
  private cartItems: EventWrapper[] = [];

  // Trigger one-time promotional overlay display
  public triggerPromoOverlay(callback: Base.Callback<emitter.EventData>): void {
    const promoEventInner: emitter.InnerEvent = {
      eventId: EventKeys.PROMO_SHOW_ID
    };
    const promoEventPayload: emitter.EventData = {
      data: {
        triggerKey: EventKeys.PROMO_SHOW_ID
      }
    };
    emitter.once(promoEventInner, callback);
    emitter.emit(promoEventInner, promoEventPayload);
  }

  // Trigger one-time promotional overlay close
  public triggerPromoClose(callback: Base.Callback<emitter.EventData>): void {
    const closeEventPayload: emitter.EventData = {
      data: {
        triggerKey: EventKeys.PROMO_CLOSE_ID
      }
    };
    emitter.once(EventKeys.PROMO_CLOSE_ID, callback);
    emitter.emit(EventKeys.PROMO_CLOSE_ID, closeEventPayload);
  }

  // Subscribe to persistent cart add events
  public subscribeCartAdd(callback: (data: emitter.EventData) => void): void {
    const addEventInner: emitter.InnerEvent = {
      eventId: EventKeys.CART_ADD_ID
    };
    emitter.off(EventKeys.CART_ADD_ID);
    emitter.on(addEventInner, (eventData: emitter.EventData) => {
      callback(eventData);
    });
  }

  // Subscribe to persistent cart remove events
  public subscribeCartRemove(callback: (data: emitter.EventData) => void): void {
    emitter.off(EventKeys.CART_REMOVE_ID);
    emitter.on(EventKeys.CART_REMOVE_ID, (eventData: emitter.EventData) => {
      callback(eventData);
    });
  }

  // Publish cart add event
  public publishCartAdd(productId: number): void {
    const addEventInner: emitter.InnerEvent = {
      eventId: EventKeys.CART_ADD_ID
    };
    const addEventPayload: emitter.EventData = {
      data: {
        itemId: productId
      }
    };
    emitter.emit(addEventInner, addEventPayload);
  }

  // Publish cart remove event
  public publishCartRemove(listIndex: number): void {
    console.info('publishCartRemove index:', JSON.stringify(listIndex));
    const removeEventPayload: emitter.EventData = {
      data: {
        itemId: listIndex
      }
    };
    emitter.emit(EventKeys.CART_REMOVE_ID, removeEventPayload);
  }

  // Subscribe to persistent purchase count event
  public startPurchaseTracking(): void {
    emitter.on(EventKeys.PURCHASE_TRACK_ID, () => {});
  }

  // Retrieve current purchase count via listener count
  public fetchPurchaseCount(callback: (count: number) => void): void {
    callback(emitter.getListenerCount(EventKeys.PURCHASE_TRACK_ID));
  }

  // Reset purchase count by unsubscribing all purchase track listeners
  public resetPurchaseCount(callback: (count: number) => void): void {
    emitter.off(EventKeys.PURCHASE_TRACK_ID);
    callback(emitter.getListenerCount(EventKeys.PURCHASE_TRACK_ID));
  }
}

Feature Breakdown

• **Promotional Overlay Display: Uses emitter.once() with a numeric event ID binds a one-time listener for the CustomDialogController trigger, auto-unsubscribing after execution.
• **Promotional Overlay Close: Uses emitter.once() with a string event ID binds a one-time listener for dismissing the CustomDialogController, auto-unsubscribing after execution.
• **Cart Item Addition: Uses emitter.on() with a numeric event ID for persistent listening, updating the cart item array whenever an add event is published.
• **Cart Item Removal: Uses emitter.on() with a string event ID for persistent listening, updating the cart item array whenever a remove event is published.
• **Purchase Count Tracking: Leverages emitter.getListenerCount() to track active purchase event listeners, displaying the result on the cart screen; resetting unsubscribes all listeners, returning a count of 0.