第21篇：ExamService 数据服务——单例模式与数据管理

一、引言

ExamService 是整个驾考应用的数据核心，负责试题管理、答题统计、成绩计算等核心功能。它采用单例模式确保全局数据一致性，并通过 @ObservedV2 / @Trace 实现响应式数据绑定。本文将深入解析 ExamService 的设计与实现。

二、单例模式

2.1 实现

@ObservedV2
export class ExamService {
  private static _instance: ExamService;
  private examDetails: ExamDetail[] = [];
  @Trace mockExamCount: number = 0;
  @Trace mockExamScore: number[] = [];
  static context: Context;

  private constructor() {
    this.examDetails = this.generateExamDetail();
  }

  public static instance(context: Context) {
    ExamService.context = context;
    if (!ExamService._instance) {
      ExamService._instance = new ExamService();
    }
    return ExamService._instance;
  }
}

2.2 使用场景

// 在组件中获取 ExamService 实例
const examService = ExamService.instance(this.getUIContext().getHostContext() as Context);

// 获取统计数据
const totalCount = examService.getTotalCount();
const didCount = examService.getDidCount();
const accuracyRate = examService.calAccuracyRate();
const averageScore = examService.calculateAverageScore();

三、核心数据统计

3.1 答题统计

// 总题数
public getTotalCount(): number {
  return this.examDetails.length;
}

// 已做题数
public getDidCount(): number {
  return this.examDetails.filter(item => item.isCorrect !== undefined).length;
}

// 正确数
public getCorrectCount(): number {
  return this.examDetails.filter(item => item.isCorrect === true).length;
}

// 错题数
public getErrorCount(): number {
  return this.examDetails.filter(item => item.isCorrect === false).length;
}

// 收藏数
public getCollectCount(): number {
  return this.examDetails.filter(item => item.isCollect === true).length;
}

3.2 正确率与平均分

// 正确率
public calAccuracyRate(): number {
  const rightCount = this.getCorrectCount();
  const totalCount = this.getTotalCount();
  if (rightCount === 0) return 0;
  return Math.ceil(rightCount / totalCount * 100);
}

// 平均分
public calculateAverageScore(): number {
  if (this.mockExamCount === 0) return 0;
  return Math.ceil(this.mockExamScore.reduce((pre, next) => pre + next) / this.mockExamCount);
}

四、试卷管理

4.1 试卷缓存

// 需要缓存的场景
const NEED_NEW_LIST = [EXAM_MANAGER_TYPE.random, EXAM_MANAGER_TYPE.error, EXAM_MANAGER_TYPE.collect];

getManagerByName(name: string | Resource, type: EXAM_MANAGER_TYPE, ...): ExamManager {
  let examManager = this.examManagerList.find(item => item.name === name);
  if (examManager === undefined || wrongOrCollect !== undefined) {
    const examList = this.getExamQuestionList(type, chapterName, name as string, wrongOrCollect);
    examManager = new ExamManager(name, examList, ...);
    // 需要缓存的场景才缓存
    NEED_NEW_LIST.indexOf(type) === -1 && this.examManagerList.push(examManager);
  }
  return examManager;
}

五、总结

ExamService 通过单例模式实现了全局数据统一管理，结合 @ObservedV2 / @Trace 实现了响应式数据绑定，为 UI 组件提供实时的数据更新。

关键源码文件：

• commons/datasource/src/main/ets/ExamService.ets