如何在服务卡片与主应用之间共享持久化数据
====================

#### 问题现象

在主应用和卡片中需要分别持久化存储数据，如何在服务卡片与主应用之间共享这些数据？

#### 背景知识

*   [Form Kit（卡片开发服务）](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/formkit-overview)提供了一种在桌面、锁屏等系统应用上嵌入显示应用信息的开发框架和API，可以将应用内用户关注的重要信息或常用操作抽取到服务卡片（简称“卡片”）上，通过将卡片添加到桌面、锁屏等系统应用上，以达到信息展示、服务直达的便捷体验效果。
*   [用户首选项(Preferences)](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/data-persistence-by-preferences)为应用提供Key-Value键值型的数据处理能力，支持应用持久化轻量级数据，并对其修改和查询。当用户有轻量级的键值型数据需要存储时，可以采用Preferences来进行存储。
*   [关系型数据库](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/data-persistence-by-rdb-store)基于SQLite组件，适用于存储包含复杂关系数据的场景，比如一个班级的学生信息，需要包括姓名、学号、各科成绩等，又或者公司的雇员信息，需要包括姓名、工号、职位等，由于数据之间有较强的对应关系，复杂程度比键值型数据更高，此时需要使用关系型数据库来持久化保存数据。

#### 解决方案

*   **解决方案一**：在服务卡片与主应用之间使用用户首选项共享持久化数据。
    1.  [创建动态卡片](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/arkts-ui-widget-creation)。
    2.  创建用户首选项操作类PreferencesHelper，该类旨在封装用户首选项（Preferences）的核心操作。为确保全局唯一性，类中定义了静态方法getInstance，以对外提供单一的PreferencesHelper实例。需要注意的是，在getPreferences函数被调用时，应先调用removePreferencesFromCacheSync方法。此操作能够主动清除已缓存的实例，强制系统从持久化文件中重新加载数据，从而保证在多线程并发访问场景下，每次获取的都是最新的首选项数据。
        
        import { preferences } from '@kit.ArkData';
        
        export class PreferencesHelper {
          private static instance: PreferencesHelper | null = null;
        
          public static getInstance() {
            if (PreferencesHelper.instance === null) {
              PreferencesHelper.instance = new PreferencesHelper();
            }
            return PreferencesHelper.instance;
          }
        
          getPreferences(context: Context, preferencesName: string): preferences.Preferences | undefined {
            try {
              preferences.removePreferencesFromCacheSync(context, preferencesName);
              return preferences.getPreferencesSync(context, { name: preferencesName });
            } catch (error) {
              let err = error as BusinessError;
              console.error(\`getPreferences failed, error code=${err.code}, message=${err.message}\`);
              return undefined;
            }
          }
        
          public get(preferences: preferences.Preferences | undefined, key: string, defaultValue: preferences.ValueType) {
            if (preferences === null || preferences === undefined) {
              return;
            }
            return preferences.getSync(key, defaultValue);
          }
        
          put(preferences: preferences.Preferences | undefined, key: string, defaultValue: preferences.ValueType) {
            if (preferences === null || preferences === undefined) {
              return;
            }
            preferences.putSync(key, defaultValue);
            preferences.flushSync();
          }
        
          clear() {
            PreferencesHelper.instance = null;
          }
        }
        
    3.  在应用主页面中，定义刷新和修改操作，从首选项获取并同步最新数据。
        
        import { PreferencesHelper } from '../utils/PreferencesHelper';
        
        @Entry
        @Component
        struct Index {
          @State curNum: number = 0;
          private readonly keyStr: string = 'restNum';
        
          build() {
            Column({ space: 15 }) {
              Text(\`当前用户首选项中数据为：${this.curNum}\`);
              Button('刷新数据').onClick(() => {
           _     // 查询最新的数据_
                this.operate(0);
              })
                .width(200);
              Row() {
                Button('减少')
                  .onClick(() => {
                    this.operate(-1);
                  });
                Button('增加')
                  .onClick(() => {
                    this.operate(1);
                  });
              }.width(200).justifyContent(FlexAlign.SpaceBetween);
            }
            .padding(16)
            .height('100%')
            .width('100%');
          }
        
         _ // 操作首选项_
          operate(value: number) {
            let utilHelper = PreferencesHelper.getInstance();
            let myPreferences =
              utilHelper.getPreferences(this.getUIContext()?.getHostContext()?.getApplicationContext()!, this.keyStr);
            let preNum = utilHelper.get(myPreferences, this.keyStr, 0) as number;
            this.curNum = preNum + value;
            if (value == 0) {
              return;
            }
            utilHelper.put(myPreferences, this.keyStr, this.curNum);
          }
        }
        
    4.  编写卡片EntryFormAbility生命周期文件。定义operate函数实现卡片端对首选项的操作，分别在onAddForm、onUpdateForm及onFormEvent中调用该操作。
        
        import { formBindingData, FormExtensionAbility, formInfo, formProvider } from '@kit.FormKit';
        import { PreferencesHelper } from '../utils/PreferencesHelper';
        
        export default class EntryFormAbility extends FormExtensionAbility {
          private readonly keyStr: string = 'restNum';
        
          operate(value: number) {
            let utilHelper = PreferencesHelper.getInstance();
            let myPreferences = utilHelper.getPreferences(this.context.getApplicationContext(), this.keyStr);
            let preNum = utilHelper.get(myPreferences, this.keyStr, 0) as number;
            let curNum = preNum + value;
            if (value == 0) {
              return curNum;
            }
            utilHelper.put(myPreferences, this.keyStr, curNum);
            return curNum;
          }
        
          onAddForm() {
           _ // Called to return a FormBindingData object._
            _// 取值_
            let curNum = this.operate(0);
           _ // 传递至卡片页面_
            return formBindingData.createFormBindingData({
              curNum: curNum
            });
          }
        
          onUpdateForm(formId: string) {
           _ // 也可取最新数据传递给卡片页面，用于定时/定点刷新等_
            let curNum = this.operate(0);
          _  // 更新_
            formProvider.updateForm(formId, formBindingData.createFormBindingData({
              curNum: curNum
            }));
          }
        
          onFormEvent(formId: string, message: string) {
            console.info('--onFormEvent--', formId, message);
          _  // 计算_
            let preNum: number = JSON.parse(message)\['curNum'\];
            let curNum = this.operate(preNum);
           _ // 更新_
            formProvider.updateForm(formId, formBindingData.createFormBindingData({
              curNum: curNum
            }));
          }
        
          onAcquireFormState() {
           _ // Called to return a {@link FormState} object._
            return formInfo.FormState.READY;
          }
        };
        
    5.  在卡片页面中，创建刷新和修改按钮，使用postCardAction发起修改操作。
        
        @Entry
        @Component
        struct WidgetCard {
          @LocalStorageProp('curNum') curNum: number = 0;
        
          operate(curNum: number) {
            postCardAction(this, {
              action: 'message',
              abilityName: 'EntryAbility',
              params: {
                curNum: curNum
              }
            });
          }
        
          build() {
            Column({ space: 15 }) {
              Text(\`当前用户首选项中数据为：${this.curNum}\`);
              Button('刷新数据').onClick(() => {
                this.operate(0);
              })
                .width(200);
              Row() {
                Button('减少')
                  .onClick(() => {
                    this.operate(-1);
                  });
                Button('增加')
                  .onClick(() => {
                    this.operate(1);
                  });
              }.width(200).justifyContent(FlexAlign.SpaceBetween);
        
            }
            .padding(16)
            .height('100%')
            .width('100%');
          }
        }
        
*   **解决方案二**：在服务卡片与主应用之间使用关系型数据库共享持久化数据。
    1.  [创建动态卡片](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/arkts-ui-widget-creation)。
    2.  创建关系型数据库的工具类RdbUtils，定义获取数据库连接、对数据库的增、删、改、查操作。接着定义Person实体类，将其作为关系型数据库操作的实体。最后，定义PersonRdbHelper类实现对Person对象在关系型数据库的操作。
        
        utils/RdbUtils.ets为：
        
        import { relationalStore } from '@kit.ArkData';
        import { BusinessError } from '@kit.BasicServicesKit';
        
        const TAG = 'RdbUtils';
        
        const STORE\_CONFIG: relationalStore.StoreConfig = {
          name: 'database.db',
          securityLevel: relationalStore.SecurityLevel.S1,
        };
        
        export class RdbUtils {
          private rdbStore?: relationalStore.RdbStore;
          private tableName: string = '';
          private sqlCreateTable: string = '';
          private context: Context;
        
          constructor(context: Context, tableName: string, sqlCreateTable: string) {
            this.context = context;
            this.tableName = tableName;
            this.sqlCreateTable = sqlCreateTable;
          }
        
          public getRdbStore(): Promise<relationalStore.RdbStore> {
            console.info(TAG, \`getRdbStore The rdbStore context: ${this.context}\`);
            return new Promise<relationalStore.RdbStore>((resolve, reject) => {
              if (this.rdbStore) {
                console.info(TAG, 'getRdbStore The rdbStore exists.');
                resolve(this.rdbStore);
              }
              relationalStore
                .getRdbStore(this.context, STORE\_CONFIG)
                .then((rdbStore: relationalStore.RdbStore) => {
                  console.info(TAG, 'getRdbStore successfully.');
                  this.rdbStore = rdbStore;
                  this.rdbStore.executeSync(this.sqlCreateTable);
                  resolve(rdbStore);
                })
                .catch((err: BusinessError) => {
                  console.error(TAG, \`getRdbStore failed, code is ${err.code},message is ${err.message}\`);
                  reject(err);
                });
            });
          }
        
          async insertData(valuesBucket: relationalStore.ValuesBucket): Promise<number> {
            console.info(TAG, \`insertData valuesBucket : ${JSON.stringify(valuesBucket)}\`);
            let rdbStore = await this.getRdbStore();
            return new Promise<number>((resolve, reject) => {
              rdbStore
                .insert(this.tableName, valuesBucket)
                .then((rowId: number) => {
                  console.info(TAG, \`insertData successfully. rowId: ${rowId}\`);
                  resolve(rowId);
                })
                .catch((err: BusinessError) => {
                  console.error(TAG, \`insertData failed, code is ${err.code},message is ${err.message}\`);
                  reject(err);
                });
            });
          }
        
          async batchInsert(valueBucketArray: Array<relationalStore.ValuesBucket>): Promise<number> {
            console.info(TAG, \`batchInsert valuesBucket : ${JSON.stringify(valueBucketArray)}\`);
            let rdbStore = await this.getRdbStore();
            return new Promise<number>((resolve, reject) => {
              rdbStore
                .batchInsert(this.tableName, valueBucketArray)
                .then((rowId: number) => {
                  console.info(TAG, \`batchInsert successfully. rowId: ${rowId}\`);
                  resolve(rowId);
                })
                .catch((err: BusinessError) => {
                  console.error(TAG, \`batchInsert failed, code is ${err.code},message is ${err.message}\`);
                  reject(err);
                });
            });
          }
        
          async deleteData(predicates: relationalStore.RdbPredicates): Promise<number> {
            let rdbStore = await this.getRdbStore();
            return new Promise<number>((resolve, reject) => {
              rdbStore
                .delete(predicates)
                .then((rows: number) => {
                  console.info(TAG, \`deleteData successfully. rows: ${rows}\`);
                  resolve(rows);
                })
                .catch((err: BusinessError) => {
                  console.error(TAG, \`deleteData failed, code is ${err.code},message is ${err.message}\`);
                  reject(err);
                });
            });
          }
        
          async updateData(predicates: relationalStore.RdbPredicates, data: relationalStore.ValuesBucket): Promise<number> {
            let rdbStore = await this.getRdbStore();
            return new Promise<number>((resolve, reject) => {
              rdbStore
                .update(data, predicates)
                .then((rows: number) => {
                  console.info(TAG, \`updateData successfully. rows: ${rows}\`);
                  resolve(rows);
                })
                .catch((err: BusinessError) => {
                  console.error(TAG, \`updateData failed, code is ${err.code},message is ${err.message}\`);
                  reject(err);
                });
            });
          }
        
          async query(predicates: relationalStore.RdbPredicates): Promise<relationalStore.ResultSet> {
            let rdbStore = await this.getRdbStore();
            return new Promise<relationalStore.ResultSet>((resolve, reject) => {
              rdbStore
                .query(predicates)
                .then((resultSet: relationalStore.ResultSet) => {
                  console.info(TAG, \`query successfully. rowCount: ${resultSet.rowCount}\`);
                  resolve(resultSet);
                })
                .catch((err: BusinessError) => {
                  console.error(TAG, \`query failed, code is ${err.code},message is ${err.message}\`);
                  reject(err);
                });
            });
          }
        }
        
        viewmodel/Person.ets为：
        
        export class Person {
          pId: string = '';
          pName: string = '';
          pAge: number = 0;
        }
        
        utils/FormRdbHelper.ets为：
        
        import { relationalStore } from '@kit.ArkData';
        import { Person } from '../viewmodel/Person';
        import { RdbUtils } from './RdbUtils';
        
        const TAG = 'PersonRdbHelper';
        
        const SQL\_CREATE\_TABLE: string =
          'CREATE TABLE IF NOT EXISTS PersonTable(pId STRING PRIMARY KEY, pName STRING, pAge NUMBER)';
        
        const TABLE\_NAME = 'PersonTable';
        let rdbUtils: RdbUtils;
        
        export class PersonRdbHelper {
          private static instance: PersonRdbHelper;
        
          private constructor(context: Context) {
            console.info(TAG, \`constructor Context: ${context}\`);
            rdbUtils = new RdbUtils(context, TABLE\_NAME, SQL\_CREATE\_TABLE);
          }
        
          public static getInstance(context: Context): PersonRdbHelper {
            if (!PersonRdbHelper.instance) {
              PersonRdbHelper.instance = new PersonRdbHelper(context);
            }
            return PersonRdbHelper.instance;
          }
        
          public insertPerson(person: Person): Promise<number> {
            console.info(TAG, \`insertPerson person: ${JSON.stringify(person)}\`);
            let valueBucket = this.generateBucket(person);
            return rdbUtils.insertData(valueBucket);
          }
        
          public deletePerson(pId: string): Promise<number> {
            console.info(TAG, \`deletePerson pId: ${pId}\`);
            let predicates = new relationalStore.RdbPredicates(TABLE\_NAME);
            predicates.equalTo('pId', pId);
            return rdbUtils.deleteData(predicates);
          }
        
          public updatePerson(person: Person): Promise<number> {
            console.info(TAG, \`updatePerson pId: ${person.pId}\`);
            let valueBucket = this.generateBucket(person);
            let predicates = new relationalStore.RdbPredicates(TABLE\_NAME);
            predicates.equalTo('pId', person.pId);
            return rdbUtils.updateData(predicates, valueBucket);
          }
        
          public queryAllPerson(): Promise<Array<Person>> {
            console.info(TAG, 'queryAllPerson');
            let predicates = new relationalStore.RdbPredicates(TABLE\_NAME);
            return this.queryPerson(predicates);
          }
        
          public queryPersonByName(formName: string): Promise<Array<Person>> {
            console.info(TAG, 'queryAllPerson');
            let predicates = new relationalStore.RdbPredicates(TABLE\_NAME);
            predicates.contains('formName', formName);
            return this.queryPerson(predicates);
          }
        
          public queryPersonById(pId: string): Promise<Person> {
            console.info(TAG, \`queryPersonById pId: ${pId}\`);
            let predicates = new relationalStore.RdbPredicates(TABLE\_NAME);
            predicates.equalTo('pId', pId);
            return new Promise<Person>(async (resolve) => {
              let personList = await this.queryPerson(predicates);
              if (personList.length > 0) {
                resolve(personList\[0\]);
              }
            });
          }
        
          public queryPerson(predicates: relationalStore.RdbPredicates): Promise<Array<Person>> {
            console.info(TAG, 'queryPerson');
            return new Promise<Array<Person>>(async (resolve) => {
              let personList: Array<Person> = \[\];
              let resultSet = await rdbUtils.query(predicates);
              while (resultSet.goToNextRow()) {
                let person: Person = new Person();
                person.pId = resultSet.getString(resultSet.getColumnIndex('pId'));
                person.pName = resultSet.getString(resultSet.getColumnIndex('pName'));
                person.pAge = resultSet.getLong(resultSet.getColumnIndex('pAge'));
                personList.push(person);
              }
              resultSet.close();
              console.info(TAG, \`queryPerson personList: ${JSON.stringify(personList)}\`);
              resolve(personList);
            });
          }
        
          private generateBucket(person: Person): relationalStore.ValuesBucket {
            let valueBucket: relationalStore.ValuesBucket = {
              pId: person.pId,
              pName: person.pName,
              pAge: person.pAge
            };
            return valueBucket;
          }
        }
        
    3.  在应用的主页面中，创建刷新和保存按钮，从数据库获取并同步刷新最新数据。
        
        import { PersonRdbHelper } from '../utils/FormRdbHelper';
        import { Person } from '../viewmodel/Person';
        import { promptAction } from '@kit.ArkUI';
        
        @Entry
        @Component
        struct Index {
          @State num: number = 0;
          @State pId: string = '';
          @State pName: string = '';
          @State pAge: number = 0;
          context: Context = this.getUIContext().getHostContext()!.getApplicationContext();
        
          onPageShow(): void {
            this.calCount();
          }
        
         _ // 计算数据库总人数_
          calCount() {
            let personRdbHelper = PersonRdbHelper.getInstance(this.context);
           _ //_
            personRdbHelper.queryAllPerson().then((persons) => {
              this.num = persons.length;
            });
          }
        
          build() {
            Column({ space: 15 }) {
              Row({ space: 10 }) {
                Text(\`当前班级总人数为${this.num}\`)
                  .fontSize(20);
                Button('刷新')
                  .onClick(() => {
                    this.calCount();
                  });
              }.width(250);
        
              Column({ space: 15 }) {
                Row() {
                  Text('学号')
                    .fontSize(20);
                  TextInput()
                    .width(200).fontSize(20).onChange((value) => {
                    this.pId = value;
                  });
                }.width('100%');
        
                Row() {
                  Text('姓名')
                    .fontSize(20);
                  TextInput().width(200).fontSize(20).onChange((value) => {
                    this.pName = value;
                  });
                }.width('100%');
        
                Row() {
                  Text('年龄')
                    .fontSize(20);
                  TextInput().width(200).type(InputType.Number).fontSize(20).onChange((value) => {
                    this.pAge = Number(value);
                  });
                }.width('100%');
        
                Button('保存至数据库').onClick(async () => {
                  let personRdbHelper = PersonRdbHelper.getInstance(this.context);
                  let res = await personRdbHelper.insertPerson({
                    pId: this.pId,
                    pName: this.pName,
                    pAge: this.pAge
                  } as Person);
                  if (res > 0) {
                    promptAction.openToast({ message: '添加成功' });
                  } else {
                    promptAction.openToast({ message: '添加失败' });
                  }
                _  // 重新计算总数_
                  this.calCount();
                }).width('100%');
              }.width(250);
            }
            .height('100%')
            .width('100%');
          }
        }
        
    4.  编写卡片EntryFormAbility生命周期文件。定义calCount函数计算数据库总人数并查询最后一个人信息，刷新卡片。
        
        import { formBindingData, FormExtensionAbility, formInfo, formProvider } from '@kit.FormKit';
        import { Want } from '@kit.AbilityKit';
        import { PersonRdbHelper } from '../utils/FormRdbHelper';
        
        export default class EntryFormAbility extends FormExtensionAbility {
          _// 计算数据库总人数_
          async calCount(formId: string) {
            let personRdbHelper = PersonRdbHelper.getInstance(this.context.getApplicationContext());
            personRdbHelper.queryAllPerson().then(persons => {
              let num = persons.length;
             _ // 封装数据_
              if (num > 0) {
                let formInfo = formBindingData.createFormBindingData({
                  num: num,
                  pId: persons\[num - 1\].pId,
                  pName: persons\[num - 1\].pName,
                  pAge: persons\[num - 1\].pAge
                });
             _   // 调用updateForm更新form_
                formProvider.updateForm(formId, formInfo);
              }
            });
          }
        
          onAddForm(want: Want) {
            if (want.parameters) {
              let formId = want.parameters\['ohos.extra.param.key.form\_identity'\] as string;
              this.calCount(formId);
            }
            return formBindingData.createFormBindingData({});
          }
        
          onUpdateForm(formId: string) {
            this.calCount(formId);
          }
        
          onFormEvent(formId: string) {
            this.calCount(formId);
          }
        
          onAcquireFormState() {
            return formInfo.FormState.READY;
          }
        };
        
    5.  在卡片页面中，渲染查询数据库的信息。创建刷新按钮，通过postCardAction完成刷新。
        
        @Entry
        @Component
        struct WidgetCard {
          @LocalStorageProp('num') num: number = 0;
          @LocalStorageProp('pId') pId: string = '还没数据';
          @LocalStorageProp('pName') pName: string = '还没数据';
          @LocalStorageProp('pAge') pAge: number = 0;
        
          build() {
            Column({ space: 15 }) {
              Row({ space: 10 }) {
                Text(\`当前班级总人数为${this.num}\`)
                  .fontSize(20);
              }.width(250);
        
              Column({ space: 15 }) {
                Row() {
                  Text(\`最后一位同学学号：${this.pId}\`)
                    .fontSize(20);
                }.width('100%');
        
                Row() {
                  Text(\`最后一位同学姓名：${this.pName}\`)
                    .fontSize(20);
                }.width('100%');
        
                Row() {
                  Text(\`最后一位同学年龄：${this.pAge}\`)
                    .fontSize(20);
                }.width('100%');
        
                Button('刷新').onClick(() => {
                  postCardAction(this, {
                    action: 'message',
                  });
                }).width('100%');
              }.width(250);
            }
            .justifyContent(FlexAlign.Center)
            .padding(16)
            .height('100%')
            .width('100%');
          }
        }
        

#### 常见FAQ

Q：是否可以使用PersistentStorage和AppStorage在应用和卡片之间进行共享持久化数据？

A：卡片和应用的主进程不是一个进程，而AppStorage是和进程绑定的，仅支持应用的主线程内多个UIAbility实例间的UI状态数据共享，所以卡片和应用主进程之间无法使用PersistentStorage和AppStorage进行状态数据共享。

Q：使用用户首选项(Preferences)共享持久化数据时，查询/更新数据时为什么每次都需要执行removePreferencesFromCache操作？

A：不同进程的内存不共享，同一进程中getPreferences只有首次会从持久化中取，所以要跨进程读取最新的持久化数据时，需先通过removePreferencesFromCache接口将Preferences实例移出缓存中的实例之后，再次getPreferences将会重新读取持久化文件，生成新的Preferences实例。

Q：为什么调用getPreferencesSync获取首选项实例时，传入的context对象为应用级的？

A：主应用和卡片属于不同的进程，不同进程的context不同。为了保证主应用和卡片获取同一个首选项实例，传入的参数应该为应用级context。

#### 总结

| 
方案

 | 

说明

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使用用户首选项共享持久化数据

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用于Key-Value键值型的数据处理。

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使用关系型数据库共享持久化数据

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用于复杂关系数据的场景。

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