Call调用是UIAbility能力的扩展，它为UIAbility提供一种能够被外部调用并与外部进行通信的能力。Call调用支持前台与后台两种启动方式，使UIAbility既能被拉起到前台展示UI，也可以在后台被创建并运行。通过建立跨进程通信（IPC）链路，它在调用方与被调用方间构建起数据通道。当在分布式场景下使用时，Call调用可以跨设备发起，使得一个设备上的应用能够将任务迁移至另一个设备上的UIAbility继续执行，从而完成跨端迁移。

Call调用的核心接口是startAbilityByCall()方法，与startAbility()接口的不同之处在于：

startAbilityByCall支持前台与后台两种启动方式，而startAbility()仅支持前台启动。
调用方可使用startAbilityByCall()所返回的Caller对象与被调用方进行通信，而startAbility()不具备通信能力。

基本概念

表1 Call调用相关名词解释

名词	描述
CallerAbility	进行Call调用的UIAbility（调用方）。
CalleeAbility	被Call调用的UIAbility（被调用方）。
Caller	实际对象，由startAbilityByCall接口返回，CallerAbility可使用Caller与CalleeAbility进行通信。
Callee	实际对象，被CalleeAbility持有，可与Caller进行通信。

约束限制

CalleeAbility的启动模式不支持指定实例模式。
当前仅分布式迁移场景对第三方应用开放Call调用权限，其余所有Call调用场景均限定为系统内部调用。

运行机制

Call调用示意图如下所示。

图1 Call调用示意图

CallerAbility调用startAbilityByCall()接口获取Caller，并使用Caller对象的call()方法向CalleeAbility发送数据。
CalleeAbility持有一个Callee对象，通过Callee的on()方法注册回调函数，当接收到Caller发送的数据时将会调用对应的回调函数。

接口说明

Call功能主要接口如下表所示。具体的API详见Caller接口说明。

表2 Call功能主要接口

接口名	描述
startAbilityByCall(want: Want): Promise<Caller>	启动指定UIAbility并获取其Caller通信接口，默认为后台启动，通过配置want可实现前台启动，详见startAbilityByCall()接口说明。AbilityContext与ServiceExtensionContext均支持该接口。
on(method: string, callback: CalleeCallBack): void	通用组件Callee注册method对应的callback方法。
off(method: string): void	通用组件Callee解注册method的callback方法。
call(method: string, data: rpc.Parcelable): Promise<void>	向通用组件Callee发送约定序列化数据。
callWithResult(method: string, data: rpc.Parcelable): Promise<rpc.MessageSequence>	向通用组件Callee发送约定序列化数据，并将Callee返回的约定序列化数据带回。
release(): void	释放通用组件的Caller通信接口。
on(type: "release", callback: OnReleaseCallback): void	注册通用组件通信断开监听通知。

开发步骤

[h2]创建Callee被调用端

在Callee被调用端，需要实现指定方法的数据接收回调函数、数据的序列化及反序列化方法。在需要接收数据期间，通过on()接口注册监听，无需接收数据时通过off()接口解除监听。

需要申请ohos.permission.DISTRIBUTED_DATASYNC权限，配置方式请参见声明权限。
同时需要在应用首次启动时弹窗向用户申请授权，使用方式请参见向用户申请授权。
配置UIAbility的启动模式。

例如将CalleeAbility配置为单实例模式singleton，配置方式请参见UIAbility组件启动模式。

定义约定的序列化数据。

调用端及被调用端发送接收的数据格式需协商一致，如下示例约定数据由number和string组成。

import { rpc } from '@kit.IPCKit';

class MyParcelable {
  num: number = 0;
  str: string = '';

  constructor(num: number, string: string) {
    this.num = num;
    this.str = string;
  }

  mySequenceable(num: number, string: string): void {
    this.num = num;
    this.str = string;
  }

  marshalling(messageSequence: rpc.MessageSequence): boolean {
    messageSequence.writeInt(this.num);
    messageSequence.writeString(this.str);
    return true;
  }

  unmarshalling(messageSequence: rpc.MessageSequence): boolean {
    this.num = messageSequence.readInt();
    this.str = messageSequence.readString();
    return true;
  }
}

实现Callee.on监听及Callee.off解除监听。

被调用端Callee的监听函数注册时机，取决于应用开发者。注册监听之前的数据不会被处理，取消监听之后的数据不会被处理。如下示例在UIAbility的onCreate()注册'MSG_SEND_METHOD'监听，在onDestroy()取消监听，收到序列化数据后作相应处理并返回，应用开发者根据实际需要做相应处理。具体示例代码如下：

import { AbilityConstant, UIAbility, Want, Caller } from '@kit.AbilityKit';
import { hilog } from '@kit.PerformanceAnalysisKit';
import { rpc } from '@kit.IPCKit';

const TAG: string = '[CalleeAbility]';
const MSG_SEND_METHOD: string = 'CallSendMsg';
const DOMAIN_NUMBER: number = 0xFF00;

class MyParcelable {
  num: number = 0;
  str: string = '';

  constructor(num: number, string: string) {
    this.num = num;
    this.str = string;
  }

  mySequenceable(num: number, string: string): void {
    this.num = num;
    this.str = string;
  }

  marshalling(messageSequence: rpc.MessageSequence): boolean {
    messageSequence.writeInt(this.num);
    messageSequence.writeString(this.str);
    return true;
  }

  unmarshalling(messageSequence: rpc.MessageSequence): boolean {
    this.num = messageSequence.readInt();
    this.str = messageSequence.readString();
    return true;
  }
}

function sendMsgCallback(data: rpc.MessageSequence): rpc.Parcelable {
  hilog.info(DOMAIN_NUMBER, TAG, '%{public}s', 'sendMsgCallback called');

  // 获取Caller发送的序列化数据
  let receivedData: MyParcelable = new MyParcelable(0, '');
  data.readParcelable(receivedData);
  hilog.info(DOMAIN_NUMBER, TAG, '%{public}s', `receiveData[${receivedData.num}, ${receivedData.str}]`);
  let num: number = receivedData.num;

  // 作相应处理
  // 返回序列化数据result给Caller
  return new MyParcelable(num + 1, `send ${receivedData.str} succeed`) as rpc.Parcelable;
}

export default class CalleeAbility extends UIAbility {
  caller: Caller | undefined;

  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    try {
      this.callee.on(MSG_SEND_METHOD, sendMsgCallback);
    } catch (error) {
      hilog.error(DOMAIN_NUMBER, TAG, '%{public}s', `Failed to register. Error is ${error}`);
    }
  }

  // ...
  releaseCall(): void {
    try {
      if (this.caller) {
        this.caller.release();
        this.caller = undefined;
      }
      hilog.info(DOMAIN_NUMBER, TAG, 'caller release succeed');
    } catch (error) {
      hilog.error(DOMAIN_NUMBER, TAG, `caller release failed with ${error}`);
    }
  }

  // ...
  onDestroy(): void {
    try {
      this.callee.off(MSG_SEND_METHOD);
      hilog.info(DOMAIN_NUMBER, TAG, '%{public}s', 'Callee OnDestroy');
      this.releaseCall();
    } catch (error) {
      hilog.error(DOMAIN_NUMBER, TAG, '%{public}s', `Failed to register. Error is ${error}`);
    }
  }
}

[h2]访问被调用端UIAbility

导入UIAbility模块。

import { UIAbility } from '@kit.AbilityKit';

获取Caller通信接口。

Ability的context属性实现了startAbilityByCall()方法，用于获取指定通用组件Caller通信接口。如下示例通过this.context获取Ability实例的context属性，使用startAbilityByCall拉起Callee被调用端并获取Caller通信接口，注册Caller的onRelease()和onRemoteStateChange()监听。应用开发者根据实际业务需要做相应处理。

import { BusinessError } from '@kit.BasicServicesKit';
import { Caller, common } from '@kit.AbilityKit';
import { hilog } from '@kit.PerformanceAnalysisKit';
import { distributedDeviceManager } from '@kit.DistributedServiceKit';
import { promptAction } from '@kit.ArkUI';

const TAG: string = '[Page_CollaborateAbility]';
const DOMAIN_NUMBER: number = 0xFF00;
let caller: Caller | undefined;
let dmClass: distributedDeviceManager.DeviceManager;

function getRemoteDeviceId(): string | undefined {
  if (typeof dmClass === 'object' && dmClass !== null) {
    let list = dmClass.getAvailableDeviceListSync();
    hilog.info(DOMAIN_NUMBER, TAG, JSON.stringify(dmClass), JSON.stringify(list));
    if (typeof (list) === 'undefined' || typeof (list.length) === 'undefined') {
      hilog.error(DOMAIN_NUMBER, TAG, 'getRemoteDeviceId err: list is null');
      return;
    }
    if (list.length === 0) {
      hilog.error(DOMAIN_NUMBER, TAG, `getRemoteDeviceId err: list is empty`);
      return;
    }
    return list[0].networkId;
  } else {
    hilog.error(DOMAIN_NUMBER, TAG, 'getRemoteDeviceId err: dmClass is null');
    return;
  }
}

@Entry
@Component
struct Page_CollaborateAbility {
  private context = this.getUIContext().getHostContext() as common.UIAbilityContext;
  build() {
    Row() {
      Column() {
        // ...
        List({ initialIndex: 0 }) {
          // ...
          ListItem() {
            Button('test').onClick(() => {
              let caller: Caller | undefined;
              let context = this.context;

              context.startAbilityByCall({
                deviceId: getRemoteDeviceId(),
                bundleName: 'com.samples.stagemodelabilityinteraction',
                abilityName: 'CalleeAbility'
              }).then((data) => {
                if (data !== null) {
                  caller = data;
                  hilog.info(DOMAIN_NUMBER, TAG, 'get remote caller success');
                  // 注册caller的release监听
                  caller.onRelease((msg) => {
                    hilog.info(DOMAIN_NUMBER, TAG, `remote caller onRelease is called ${msg}`);
                  });
                  hilog.info(DOMAIN_NUMBER, TAG, 'remote caller register OnRelease succeed');
                  promptAction.openToast({
                    message: 'CallerSuccess'
                  });
                  // 注册caller的协同场景下跨设备组件状态变化监听通知
                  try {
                    caller.onRemoteStateChange((str) => {
                      hilog.info(DOMAIN_NUMBER, TAG, 'Remote state changed ' + str);
                    });
                  } catch (error) {
                    hilog.error(DOMAIN_NUMBER, TAG, `Caller.onRemoteStateChange catch error, error.code: ${JSON.stringify(error.code)}, error.message: ${JSON.stringify(error.message)}`);
                  }
                }
              }).catch((error: BusinessError) => {
                hilog.error(DOMAIN_NUMBER, TAG, `get remote caller failed with ${error}`);
              });
            })
          }
          // ...
        }
        // ...
      }
      // ...
    }
  }
}

[h2]向被调用端UIAbility发送约定序列化数据

向被调用端发送Parcelable数据有两种方式，一种是不带返回值，一种是获取被调用端返回的数据，method以及序列化数据需要与被调用端协商一致。如下示例调用Call接口，向Callee被调用端发送数据。

import { UIAbility, Caller } from '@kit.AbilityKit';
import { rpc } from '@kit.IPCKit';
import { hilog } from '@kit.PerformanceAnalysisKit';

const TAG: string = '[CalleeAbility]';
const DOMAIN_NUMBER: number = 0xFF00;
const MSG_SEND_METHOD: string = 'CallSendMsg';

class MyParcelable {
  num: number = 0;
  str: string = '';

  constructor(num: number, string: string) {
    this.num = num;
    this.str = string;
  }

  mySequenceable(num: number, string: string): void {
    this.num = num;
    this.str = string;
  }

  marshalling(messageSequence: rpc.MessageSequence): boolean {
    messageSequence.writeInt(this.num);
    messageSequence.writeString(this.str);
    return true;
  }

  unmarshalling(messageSequence: rpc.MessageSequence): boolean {
    this.num = messageSequence.readInt();
    this.str = messageSequence.readString();
    return true;
  }
}

export default class EntryAbility extends UIAbility {
  // ...
  caller: Caller | undefined;

  async onButtonCall(): Promise<void> {
    try {
      let msg: MyParcelable = new MyParcelable(1, 'origin_Msg');
      if (this.caller) {
        await this.caller.call(MSG_SEND_METHOD, msg);
      }
    } catch (error) {
      hilog.error(DOMAIN_NUMBER, TAG, `caller call failed with ${error}`);
    }
  }
  // ...
}

如下示例调用callWithResult()接口，向Callee被调用端发送待处理的数据originMsg，并将CallSendMsg方法处理完毕的数据赋值给backMsg。

import { UIAbility, Caller } from '@kit.AbilityKit';
import { rpc } from '@kit.IPCKit';
import { hilog } from '@kit.PerformanceAnalysisKit';

const TAG: string = '[CalleeAbility]';
const DOMAIN_NUMBER: number = 0xFF00;

const MSG_SEND_METHOD: string = 'CallSendMsg';
let originMsg: string = '';
let backMsg: string = '';

class MyParcelable {
  num: number = 0;
  str: string = '';

  constructor(num: number, string: string) {
    this.num = num;
    this.str = string;
  }

  mySequenceable(num: number, string: string): void {
    this.num = num;
    this.str = string;
  }

  marshalling(messageSequence: rpc.MessageSequence): boolean {
    messageSequence.writeInt(this.num);
    messageSequence.writeString(this.str);
    return true;
  }

  unmarshalling(messageSequence: rpc.MessageSequence): boolean {
    this.num = messageSequence.readInt();
    this.str = messageSequence.readString();
    return true;
  }
}

export default class EntryAbility extends UIAbility {
  // ...
  caller: Caller | undefined;

  async onButtonCallWithResult(originMsg: string, backMsg: string): Promise<void> {
    try {
      let msg: MyParcelable = new MyParcelable(1, originMsg);
      if (this.caller) {
        const data = await this.caller.callWithResult(MSG_SEND_METHOD, msg);
        hilog.info(DOMAIN_NUMBER, TAG, 'caller callWithResult succeed');
        let result: MyParcelable = new MyParcelable(0, '');
        data.readParcelable(result);
        backMsg = result.str;
        hilog.info(DOMAIN_NUMBER, TAG, `caller result is [${result.num}, ${result.str}]`);
      }
    } catch (error) {
      hilog.error(DOMAIN_NUMBER, TAG, `caller callWithResult failed with ${error}`);
    }
  }
  // ...
}

[h2]释放Caller通信接口

Caller不再使用后，应用开发者可以通过release()接口释放Caller。

import { UIAbility, Caller } from '@kit.AbilityKit';
import { hilog } from '@kit.PerformanceAnalysisKit';

const TAG: string = '[CalleeAbility]';
const DOMAIN_NUMBER: number = 0xFF00;

export default class EntryAbility extends UIAbility {
  caller: Caller | undefined
  releaseCall(): void {
    try {
      if (this.caller) {
        this.caller.release();
        this.caller = undefined;
      }
      hilog.info(DOMAIN_NUMBER, TAG, 'caller release succeed');
    } catch (error) {
      hilog.error(DOMAIN_NUMBER, TAG, `caller release failed with ${error}`);
    }
  }
}

目录

通过Call调用实现多端协同