HarmonyOS基础技术赋能之分布式数据服务功能 原创 精华

引言    
分布式数据服务（Distributed Data Service，DDS） 为应用程序提供不同设备间数据库数据分布式的能力。通过调用分布式数据接口，应用程序将数据保存到分布式数据库中。通过结合帐号、应用和数据库三元组，分布式数据服务对属于不同应用的数据进行隔离，保证不同应用之间的数据不能通过分布式数据服务互相访问。在通过可信认证的设备间，分布式数据服务支持应用数据相互同步，为用户提供在多种终端设备上最终一致的数据访问体验。

功能介绍
此次通过HarmonyOS的分布式数据服务能力，一方面可以实现自身应用界面的数据实时更新；另一方面也可以实现不同设备之间的数据实时更新。前提是在不同设备之间，要实现分布式数据服务的同步能力，需要同一个华为账号登录、并一个应用包名、同一个网络之间进行，也可以两个设备同时开启蓝牙。

开发指南
1. 在config.json中添加permisssion权限。

// 添加在abilities同一目录层级
"reqPermissions": [
    {
        "name": "ohos.permission.DISTRIBUTED_DATASYNC"
    }
]

2. 在MainAbility中添加权限

@Override
public void onStart(Intent intent) {
  super.onStart(intent);
  super.setMainRoute(MainAbilitySlice.class.getName());
  //实现Ability的代码中显式声明需要使用多设备协同访问的权限
  requestPermissionsFromUser(new String[]{
      "ohos.permission.DISTRIBUTED_DATASYNC"}, 0);

}

3. 根据配置构造分布式数据库管理类实例KvManager以及创建分布式数据库对象SingleKvStore。

//实现数据库的初始化
// 初入的参数context: Context context = getApplicationContext()获得；storeId为分布式数据库id,String类型，可自行定义，例如“testApp”。
public static SingleKvStore initOrGetDB(Context context, String storeId) {
  KvManagerConfig kvManagerConfig = new KvManagerConfig(context);
  kvManager = KvManagerFactory.getInstance().createKvManager(kvManagerConfig);
  Options options = new Options();
  options.setCreateIfMissing(true)
    .setEncrypt(false)
    .setKvStoreType(KvStoreType.SINGLE_VERSION) //数据库类型：单版本分布式数据库
    .setAutoSync(true);//设置数据为自动同步
  singleKvStore = kvManager.getKvStore(options, storeId);
  return singleKvStore;
}

4. 将数据写入单版本分布式数据库。

//以key-value形式存储到分布式数据库
try {
  long id = System.currentTimeMillis();
  singleKvStore.putString("key",
      "{\"id\":" + id +
          ",\"temp\":" + temperature +
          ",\"humidity\":" + humidity +
          ",\"NH4\":" + 0.0 +
          ",\"H2S\":" + 0.0 +
          ",\"other\":" + gas + "}");
} catch (KvStoreException e) {
  e.printStackTrace();
}

5.订阅分布式数据变化。客户端需要实现KvStoreObserver接口，监听数据变化。

try {
//订阅类型SubscribeType.SUBSCRIBE_TYPE_ALL意思可以同步到本机和其他外围设备
  innerKvStoreObserver = new InnerKvStoreObserver();
  singleKvStore.subscribe(SubscribeType.SUBSCRIBE_TYPE_ALL, innerKvStoreObserver);
} catch (KvStoreException e) {
  e.printStackTrace();
}

public class InnerKvStoreObserver implements KvStoreObserver {

  @Override
  public void onChange(ChangeNotification changeNotification) {
    //刷新页面上的数据，同样有一个坑，onChange方法实质上，在一个子线程里执行
    MainAbilitySlice.taskDispatcher.asyncDispatch(() -> {
      //在这里执行页面ui组件的显示刷新
      flushUIData();
    });
  }
}

6.获取分布式数据库数据

private void flushUIData() {
  //查询分布式数据的数据，获取数据可以通过get（String key）/ getEntries(String key)方法获取数据
  List<Entry> entries = singleKvStore.getEntries(“key”);
  if (entries.size() > 0) {
    ZSONObject zsonObject = ZSONObject.stringToZSON(entries.get(0).getValue().getString());
    int temp = zsonObject.getIntValue("temp");
    int humidity = zsonObject.getIntValue("humidity");
    int other = zsonObject.getIntValue("other");
    tvTemp.setText(temp+"℃");
    tvHumi.setText(humidity+"% RH");
    tvGas.setText(other+"% LEL");
  }

7. 解除订阅。一般在页面销毁时调用，也就是MainAbilitySlice的onStop()中调用

if (singleKvStore != null) {
  singleKvStore.unSubscribe(innerKvStoreObserver);
}

8. 同步数据到其他设备。获取已连接的设备列表，选择同步方式进行数据同步

List<DeviceInfo> deviceInfoList = kvManager.getConnectedDevicesInfo(DeviceFilterStrategy.NO_FILTER);
List<String> deviceIdList = new ArrayList<>();
for (DeviceInfo deviceInfo : deviceInfoList) {
    deviceIdList.add(deviceInfo.getId());
}
singleKvStore.sync(deviceIdList, SyncMode.PUSH_ONLY);

项目中采用在后台service中开启定时任务，实时保存数据到分布式数据库，然后在主界面，监听数据变化，实时更新数据。

结果演示

1.刚开始安装完成后效果：

2.每隔3秒，界面数据都会发生变化：

附上源码：

1.MainAbilitySlice

public class MainAbilitySlice extends AbilitySlice {
  private SingleKvStore singleKvStore;
  private Text tvTemp;
  private Text tvHumi;
  private Text tvGas;
  private Intent serviceIntent;
  private InnerKvStoreObserver innerKvStoreObserver;

  @Override
  public void onStart(Intent intent) {
    super.onStart(intent);
    super.setUIContent(ResourceTable.Layout_ability_main);
    tvTemp=(Text)findComponentById(ResourceTable.Id_tvTemp);
    tvHumi=(Text)findComponentById(ResourceTable.Id_tvHumi);
    tvGas=(Text)findComponentById(ResourceTable.Id_tvGas);
    initService();

    try {
      //获取数据库
      singleKvStore = DBUtils.initOrGetDB(this, DBUtils.STORE_ID);
      innerKvStoreObserver = new InnerKvStoreObserver();
      singleKvStore.subscribe(SubscribeType.SUBSCRIBE_TYPE_ALL, innerKvStoreObserver);
    } catch (KvStoreException e) {
      e.printStackTrace();
    }
  }

  public class InnerKvStoreObserver implements KvStoreObserver {

    @Override
    public void onChange(ChangeNotification changeNotification) {
      //刷新页面上的数据，同样有一个坑，onChange方法实质上，在一个子线程里执行
      getUITaskDispatcher().asyncDispatch(() -> {
        //在这里执行页面ui组件的显示刷新
        flushUIData();
      });
    }
  }

  private void flushUIData() {
    //查询分布式数据的数据
    List<Entry> entries = singleKvStore.getEntries("key");
    if (entries.size() > 0) {
      ZSONObject zsonObject = ZSONObject.stringToZSON(entries.get(0).getValue().getString());
      int temp = zsonObject.getIntValue("temp");
      int humidity = zsonObject.getIntValue("humidity");
      int other = zsonObject.getIntValue("other");
      tvTemp.setText(temp+"℃");
      tvHumi.setText(humidity+"% RH");
      tvGas.setText(other+"% LEL");
    }



  }

  private void initService() {
    //启动ServiceAbility
     serviceIntent = new Intent();
    Operation operation = new Intent.OperationBuilder()
        .withDeviceId("")
        .withBundleName("com.isoftstone.kvstoreapp")
        .withAbilityName("com.isoftstone.kvstoreapp.ServiceAbility")
        .build();
    serviceIntent.setOperation(operation);
    startAbility(serviceIntent);
  }

  @Override
  public void onActive() {
    super.onActive();
  }

  @Override
  public void onForeground(Intent intent) {
    super.onForeground(intent);
  }

  @Override
  protected void onStop() {
    super.onStop();
    //销毁service
   stopAbility(serviceIntent);
   //删除数据库
   DBUtils.clearDB();
    //解除订阅
    if (singleKvStore != null) {
      singleKvStore.unSubscribe(innerKvStoreObserver);
    }
  }
}

2.ServiceAbility

public class ServiceAbility extends Ability {

  private static final HiLogLabel LABEL_LOG = new HiLogLabel(3, 0xD001100, "Demo");
  private SingleKvStore singleKvStore;
  private Timer timer;
  private MyTimerTask myTimerTask;
  private int temperature;
  private int humidity;
  private int gas;

  @Override
  public void onStart(Intent intent) {
    super.onStart(intent);
    singleKvStore = DBUtils.initOrGetDB(this, DBUtils.STORE_ID);
    timer=new Timer();
    myTimerTask=new MyTimerTask();
    timer.schedule(myTimerTask,0,3000);

  }

  @Override
  public void onBackground() {
    super.onBackground();
    HiLog.info(LABEL_LOG, "ServiceAbility::onBackground");
  }

  @Override
  public void onStop() {
    super.onStop();
    if(myTimerTask!=null){
      myTimerTask.cancel();
    }
    if(timer!=null){
      timer.cancel();
    }
  }

  @Override
  public void onCommand(Intent intent, boolean restart, int startId) {
  }

  @Override
  public IRemoteObject onConnect(Intent intent) {
    return null;
  }

  @Override
  public void onDisconnect(Intent intent) {
  }

  private class MyTimerTask extends TimerTask{

    @Override
    public void run() {
      temperature++;
      humidity++;
      gas++;
      try {
        long id = System.currentTimeMillis();
        singleKvStore.putString("key",
            "{\"id\":" + id +
                ",\"temp\":" + temperature +
                ",\"humidity\":" + humidity +
                ",\"NH4\":" + 0.0 +
                ",\"H2S\":" + 0.0 +
                ",\"other\":" + gas + "}");
      } catch (KvStoreException e) {
        e.printStackTrace();
      }

    }
  }
}

3．DBUtils

public class DBUtils {
  //分布式数据库storeId
  public static final String STORE_ID="kvStoreDB";
  private static KvManager kvManager;
  private static SingleKvStore singleKvStore;


  //具体的实现数据库的初始化
  public static SingleKvStore initOrGetDB(Context context, String storeId) {

    KvManagerConfig kvManagerConfig = new KvManagerConfig(context);
    kvManager = KvManagerFactory.getInstance().createKvManager(kvManagerConfig);
    Options options = new Options();
    options.setCreateIfMissing(true)
        .setEncrypt(false)
        .setKvStoreType(KvStoreType.SINGLE_VERSION)
        .setAutoSync(true);//设置数据为自动同步
    singleKvStore = kvManager.getKvStore(options, storeId);
    return singleKvStore;
  }

  // 如果数据库中的字段有修改，只能先关闭，后删除，然后重新创建才生效
  public static void clearDB() {
    kvManager.closeKvStore(singleKvStore);
    kvManager.deleteKvStore(STORE_ID);
  }


}

4． MainAbility

public class MainAbility extends Ability {

  @Override
  public void onStart(Intent intent) {
    super.onStart(intent);
    super.setMainRoute(MainAbilitySlice.class.getName());
    //实现Ability的代码中显式声明需要使用多设备协同访问的权限
    requestPermissionsFromUser(new String[]{
        "ohos.permission.DISTRIBUTED_DATASYNC"}, 0);
  }
}

5. MyApplication

public class MyApplication extends AbilityPackage {

  @Override
  public void onInitialize() {
    super.onInitialize();
  }
}

6. config.json 文件

{
  "app": {
    "bundleName": "com.isoftstone.healthdata",
    "vendor": "isoftstone",
    "version": {
      "code": 1000000,
      "name": "1.0"
    },
    "apiVersion": {
      "compatible": 4,
      "target": 5,
      "releaseType": "Release"
    }
  },
  "deviceConfig": {},
  "module": {
    "package": "com.isoftstone.kvstoreapp",
    "name": ".MyApplication",
    "deviceType": [
      "phone"
    ],
    "distro": {
      "deliveryWithInstall": true,
      "moduleName": "entry",
      "moduleType": "entry"
    },
    "reqPermissions": [
      {
        "name": "ohos.permission.DISTRIBUTED_DATASYNC"
      }
    ],
    "abilities": [
      {
        "skills": [
          {
            "entities": [
              "entity.system.home"
            ],
            "actions": [
              "action.system.home"
            ]
          }
        ],
        "orientation": "unspecified",
        "name": "com.isoftstone.kvstoreapp.MainAbility",
        "icon": "$media:icon",
        "description": "$string:mainability_description",
        "label": "$string:app_name",
        "type": "page",
        "launchType": "standard"
      },
      {
        "name": "com.isoftstone.kvstoreapp.ServiceAbility",
        "icon": "$media:icon",
        "description": "$string:serviceability_description",
        "type": "service"
      }
    ]
  }
}

7.xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
  xmlns:ohos="http://schemas.huawei.com/res/ohos"
  ohos:height="match_parent"
  ohos:orientation="vertical"
  ohos:width="match_parent">

<DirectionalLayout
  ohos:padding="20vp"
  ohos:height="match_content"
  ohos:width="match_parent"
  ohos:orientation="horizontal">
  <Text
    ohos:width="match_content"
    ohos:height="match_content"
    ohos:text_size="20vp"
    ohos:text="温度："/>
  <Text
    ohos:id="$+id:tvTemp"
    ohos:width="0"
    ohos:height="match_content"
    ohos:text_size="22vp"
    ohos:text_color="#00ff00"
    ohos:text="待采集..."
    ohos:weight="1"/>
</DirectionalLayout>
  <DirectionalLayout
    ohos:height="1vp"
    ohos:width="match_parent"
    ohos:background_element="#cccccc"/>

  <DirectionalLayout
    ohos:padding="20vp"
    ohos:height="match_content"
    ohos:width="match_parent"
    ohos:orientation="horizontal">
    <Text
      ohos:width="match_content"
      ohos:height="match_content"
      ohos:text_size="20vp"
      ohos:text="湿度："/>
    <Text
      ohos:id="$+id:tvHumi"
      ohos:width="0"
      ohos:height="match_content"
      ohos:text_size="22vp"
      ohos:text_color="#00ff00"
      ohos:text="待采集..."
      ohos:weight="1"/>
  </DirectionalLayout>
  <DirectionalLayout
    ohos:height="1vp"
    ohos:width="match_parent"
    ohos:background_element="#cccccc"/>


  <DirectionalLayout
    ohos:padding="20vp"
    ohos:height="match_content"
    ohos:width="match_parent"
    ohos:orientation="horizontal">
    <Text
      ohos:width="match_content"
      ohos:height="match_content"
      ohos:text_size="20vp"
      ohos:text="可燃气体："/>
    <Text
      ohos:id="$+id:tvGas"
      ohos:width="0"
      ohos:height="match_content"
      ohos:text_size="22vp"
      ohos:text_color="#00ff00"
      ohos:text="待采集..."
      ohos:weight="1"/>
  </DirectionalLayout>
  <DirectionalLayout
    ohos:height="1vp"
    ohos:width="match_parent"
    ohos:background_element="#cccccc"/>

</DirectionalLayout>

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