Background Task Management Development

When to Use

If a service needs to be continued when the application or service module is running in the background (not visible to users), the application or service module can request a transient task to delay the suspension or a continuous task to prevent the suspension. The application can also request efficiency resources in the following scenarios for more flexibility:

• The application should not be suspended within a period of time until it finishes the task.

• The application requires system resources even when it is suspended. For example, an alarm clock requires timer resources even when being suspended.

• The application needs to execute the task at an unlimited frequency and within a longer time.

Transient Tasks

Available APIs

Table 1 Main APIs for transient tasks

How to Develop

1. Request a suspension delay.

   import backgroundTaskManager from '@ohos.backgroundTaskManager';
   
   
   let myReason = 'test requestSuspendDelay';
   let delayInfo = backgroundTaskManager.requestSuspendDelay(myReason, () => {
       console.info("Request suspension delay will time out.");
   });
   
   
   var id = delayInfo.requestId;
   console.info("requestId is: " + id);
   

2. Obtain the remaining duration before the application is suspended.

   backgroundTaskManager.getRemainingDelayTime(id).then( res => {
       console.log('promise => Operation getRemainingDelayTime succeeded. Data: ' + JSON.stringify(res));
   }).catch( err => {
       console.log('promise => Operation getRemainingDelayTime failed. Cause: ' + err.code);
   });
   

3. Cancel the suspension delay.

   backgroundTaskManager.cancelSuspendDelay(id);
   

Development Examples

import backgroundTaskManager from '@ohos.backgroundTaskManager';
let myReason = 'test requestSuspendDelay';

// Request a suspension delay.
let delayInfo = backgroundTaskManager.requestSuspendDelay(myReason, () => {
    console.info("Request suspension delay will time out.");
});

// Print the suspension delay information.
var id = delayInfo.requestId;
var time = delayInfo.actualDelayTime;
console.info("The requestId is: " + id);
console.info("The actualDelayTime is: " + time);

// Obtain the remaining duration before the application is suspended.
backgroundTaskManager.getRemainingDelayTime(id).then( res => {
    console.log('promise => Operation getRemainingDelayTime succeeded. Data: ' + JSON.stringify(res));
}).catch( err => {
    console.log('promise => Operation getRemainingDelayTime failed. Cause: ' + err.code);
});

// Cancel the suspension delay.
backgroundTaskManager.cancelSuspendDelay(id);

Continuous Tasks

Required Permissions

ohos.permission.KEEP_BACKGROUND_RUNNING

Available APIs

Table 2 Main APIs for continuous tasks

For details about wantAgent, see WantAgent.

Table 3 Background modes

How to Develop

Development on the FA model:

1. Create an API version 8 project. Then right-click the project directory and choose New > Ability > Service Ability to create a Service ability. Configure the continuous task permission and background mode type in the config.json file, with the ability type set to service.

   "module": {
     "package": "com.example.myapplication",
     "abilities": [
       {
         "backgroundModes": [
           "dataTransfer",
           "location"
         ], // Background mode
         "type": "service"  // The ability type is service.
       }
     ],
     "reqPermissions": [
       {
         "name": "ohos.permission.KEEP_BACKGROUND_RUNNING" // Continuous task permission
       }
     ]
   }
   

2. Request a continuous task.

   import backgroundTaskManager from '@ohos.backgroundTaskManager';
   import featureAbility from '@ohos.ability.featureAbility';
   import wantAgent from '@ohos.wantAgent';
   
   
   let wantAgentInfo = {
       wants: [
           {
               bundleName: "com.example.myapplication",
               abilityName: "com.example.myapplication.MainAbility"
           }
       ],
       operationType: wantAgent.OperationType.START_ABILITY,
       requestCode: 0,
       wantAgentFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
   };
   
   
   // Obtain the WantAgent object by using the getWantAgent API of the wantAgent module.
   wantAgent.getWantAgent(wantAgentInfo).then((wantAgentObj) => {
       backgroundTaskManager.startBackgroundRunning(featureAbility.getContext(),
           backgroundTaskManager.BackgroundMode.DATA_TRANSFER, wantAgentObj).then(() => {
           console.info("Operation startBackgroundRunning succeeded");
       }).catch((err) => {
           console.error("Operation startBackgroundRunning failed Cause: " + err);
       });
   });
   

3. Cancel the continuous task.

   import backgroundTaskManager from '@ohos.backgroundTaskManager';
   import featureAbility from '@ohos.ability.featureAbility';
   
   
   backgroundTaskManager.stopBackgroundRunning(featureAbility.getContext()).then(() => {
       console.info("Operation stopBackgroundRunning succeeded");
   }).catch((err) => {
       console.error("Operation stopBackgroundRunning failed Cause: " + err);
   });
   
   
   

Development on the stage model:

1. Create an API version 9 project. Then right-click the project directory and choose New > Ability to create an ability. Configure the continuous task permission and background mode type in the module.json5 file.

   "module": {
     "abilities": [
       {
         "backgroundModes": [
           "dataTransfer",
           "location"
         ], // Background mode
       }
     ],
     "requestPermissions": [
       {
         "name": "ohos.permission.KEEP_BACKGROUND_RUNNING" // Continuous task permission
       }
     ]
   }
   

2. Request a continuous task.

   import backgroundTaskManager from '@ohos.backgroundTaskManager';
   import wantAgent from '@ohos.wantAgent';
   
   
   let wantAgentInfo = {
       wants: [
           {
               bundleName: "com.example.myapplication",
               abilityName: "com.example.myapplication.MainAbility"
           }
       ],
       operationType: wantAgent.OperationType.START_ABILITY,
       requestCode: 0,
       wantAgentFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
   };
   
   
   // Obtain the WantAgent object by using the getWantAgent API of the wantAgent module.
   wantAgent.getWantAgent(wantAgentInfo).then((wantAgentObj) => {
       backgroundTaskManager.startBackgroundRunning(this.context,
           backgroundTaskManager.BackgroundMode.DATA_TRANSFER, wantAgentObj).then(() => {
           console.info("Operation startBackgroundRunning succeeded");
       }).catch((err) => {
           console.error("Operation startBackgroundRunning failed Cause: " + err);
       });
   });
   

3. Cancel the continuous task.

   import backgroundTaskManager from '@ohos.backgroundTaskManager';
   
   
   backgroundTaskManager.stopBackgroundRunning(this.context).then(() => {
       console.info("Operation stopBackgroundRunning succeeded");
   }).catch((err) => {
       console.error("Operation stopBackgroundRunning failed Cause: " + err);
   });
   
   
   

Development Examples

Development on the FA model:

For details about how to use the Service ability in the FA model, see Service Ability Development.

If an application does not need to interact with a continuous task in the background, you can use startAbility() to start the Service ability. In the onStart callback of the Service ability, call startBackgroundRunning() to declare that the Service ability needs to run in the background for a long time. After the task execution is complete, call stopBackgroundRunning() to release resources.

If an application needs to interact with a continuous task in the background (for example, an application related to music playback), you can use connectAbility() to start and connect to the Service ability. After obtaining the proxy of the Service ability, the application can communicate with the Service ability and control the request and cancellation of continuous tasks.

import backgroundTaskManager from '@ohos.backgroundTaskManager';
import featureAbility from '@ohos.ability.featureAbility';
import wantAgent from '@ohos.wantAgent';
import rpc from "@ohos.rpc";

function startContinuousTask() {
    let wantAgentInfo = {
        // List of operations to be executed after the notification is clicked.
        wants: [
            {
                bundleName: "com.example.myapplication",
                abilityName: "com.example.myapplication.MainAbility"
            }
        ],
        // Type of the operation to perform after the notification is clicked.
        operationType: wantAgent.OperationType.START_ABILITY,
        // Custom request code.
        requestCode: 0,
        // Execution attribute of the operation to perform after the notification is clicked.
        wantAgentFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
    };

    // Obtain the WantAgent object by using the getWantAgent API of the wantAgent module.
    wantAgent.getWantAgent(wantAgentInfo).then((wantAgentObj) => {
        backgroundTaskManager.startBackgroundRunning(featureAbility.getContext(),
            backgroundTaskManager.BackgroundMode.DATA_TRANSFER, wantAgentObj).then(() => {
            console.info("Operation startBackgroundRunning succeeded");
        }).catch((err) => {
            console.error("Operation startBackgroundRunning failed Cause: " + err);
        });
    });
}

function stopContinuousTask() {
    backgroundTaskManager.stopBackgroundRunning(featureAbility.getContext()).then(() => {
        console.info("Operation stopBackgroundRunning succeeded");
    }).catch((err) => {
        console.error("Operation stopBackgroundRunning failed Cause: " + err);
    });
}

async function processAsyncJobs() {
    // Execute the continuous task.

    // After the continuous task is complete, call the API to release resources.
    stopContinuousTask();
}

let mMyStub;

class MyStub extends rpc.RemoteObject {
    constructor(des) {
        if (typeof des === 'string') {
            super(des);
        } else {
            return null;
        }
    }
    onRemoteRequest(code, data, reply, option) {
        console.log('ServiceAbility onRemoteRequest called');
        // The meaning of code is user-defined.
        if (code === 1) {
            // Receive the request code for requesting a continuous task.
            startContinuousTask();
            // Execute the continuous task.
        } else if (code === 2) {
            // Receive the request code for canceling the continuous task.
            stopContinuousTask();
        } else {
            console.log('ServiceAbility unknown request code');
        }
        return true;
    }
}

export default {
    onStart(want) {
        console.info('ServiceAbility onStart');
        mMyStub = new MyStub("ServiceAbility-test");
        // Call the API to start the task.
        startContinuousTask();
        processAsyncJobs();
    },
    onStop() {
        console.info('ServiceAbility onStop');
    },
    onConnect(want) {
        console.info('ServiceAbility onConnect');
        return mMyStub;
    },
    onReconnect(want) {
        console.info('ServiceAbility onReconnect');
    },
    onDisconnect() {
        console.info('ServiceAbility onDisconnect');
    },
    onCommand(want, restart, startId) {
        console.info('ServiceAbility onCommand');
    }
};

Development on the stage model:

For details about the stage model, see Stage Model Overview. If an application needs to run a continuous task in the background, you can use Call to create and run an ability in the background. For details, see Call Development.

import Ability from '@ohos.application.Ability'
import backgroundTaskManager from '@ohos.backgroundTaskManager';
import wantAgent from '@ohos.wantAgent';

let mContext = null;

function startContinuousTask() {
    let wantAgentInfo = {
        // List of operations to be executed after the notification is clicked.
        wants: [
            {
                bundleName: "com.example.myapplication",
                abilityName: "com.example.myapplication.MainAbility"
            }
        ],
        // Type of the operation to perform after the notification is clicked.
        operationType: wantAgent.OperationType.START_ABILITY,
        // Custom request code.
        requestCode: 0,
        // Execution attribute of the operation to perform after the notification is clicked.
        wantAgentFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
    };

    // Obtain the WantAgent object by using the getWantAgent API of the wantAgent module.
    wantAgent.getWantAgent(wantAgentInfo).then((wantAgentObj) => {
        backgroundTaskManager.startBackgroundRunning(mContext,
            backgroundTaskManager.BackgroundMode.DATA_TRANSFER, wantAgentObj).then(() => {
            console.info("Operation startBackgroundRunning succeeded");
        }).catch((err) => {
            console.error("Operation startBackgroundRunning failed Cause: " + err);
        });
    });
}

function stopContinuousTask() {
    backgroundTaskManager.stopBackgroundRunning(mContext).then(() => {
        console.info("Operation stopBackgroundRunning succeeded");
    }).catch((err) => {
        console.error("Operation stopBackgroundRunning failed Cause: " + err);
    });
}

class MySequenceable {
    num: number = 0;
    str: String = "";

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

    marshalling(messageParcel) {
        messageParcel.writeInt(this.num);
        messageParcel.writeString(this.str);
        return true;
    }

    unmarshalling(messageParcel) {
        this.num = messageParcel.readInt();
        this.str = messageParcel.readString();
        return true;
    }
}

function sendMsgCallback(data) {
    console.info('BgTaskAbility funcCallBack is called ' + data)
    let receivedData = new Mysequenceable(0, "")
    data.readSequenceable(receivedData)
    console.info(`receiveData[${receivedData.num}, ${receivedData.str}]`)
    if (receivedData.str === 'start_bgtask') {
        startContinuousTask()
    } else if (receivedData.str === 'stop_bgtask') {
        stopContinuousTask();
    }
    return new Mysequenceable(10, "Callee test");
}

export default class BgTaskAbility extends Ability {
    onCreate(want, launchParam) {
        console.info("[Demo] BgTaskAbility onCreate")
        this.callee.on("test", sendMsgCallback);

        try {
            this.callee.on(MSG_SEND_METHOD, sendMsgCallback)
        } catch (error) {
            console.error(`${MSG_SEND_METHOD} register failed with error ${JSON.stringify(error)}`)
        }
        mContext = this.context;
    }

    onDestroy() {
        console.info("[Demo] BgTaskAbility onDestroy")
    }

    onWindowStageCreate(windowStage) {
        console.info("[Demo] BgTaskAbility onWindowStageCreate")

        windowStage.loadContent("pages/second").then((data)=> {
            console.info(`load content succeed with data ${JSON.stringify(data)}`)
        }).catch((error)=>{
            console.error(`load content failed with error ${JSON.stringify(error)}`)
        })
    }

    onWindowStageDestroy() {
        console.info("[Demo] BgTaskAbility onWindowStageDestroy")
    }

    onForeground() {
        console.info("[Demo] BgTaskAbility onForeground")
    }

    onBackground() {
        console.info("[Demo] BgTaskAbility onBackground")
    }
};

Efficiency Resources

Available APIs

Table 4 Main APIs for efficiency resources

How to Develop

1. Request efficiency resources.

import backgroundTaskManager from '@ohos.backgroundTaskManager';

let request = {
    resourceTypes: backgroundTaskManager.ResourceType.CPU,
    isApply: true,
    timeOut: 0,
    reason: "apply",
    isPersist: true,
    isProcess: true,
};
let res = backgroundTaskManager.applyEfficiencyResources(request);
console.info("the result of request is: " + res);

1. Release some efficiency resources.

import backgroundTaskManager from '@ohos.backgroundTaskManager';

let request = {
    resourceTypes: backgroundTaskManager.ResourceType.CPU,
    isApply: false,
    timeOut: 0,
    reason: "reset",
};
let res = backgroundTaskManager.applyEfficiencyResources(request);
console.info("the result of request is: " + res);

1. Release all efficiency resources.

import backgroundTaskManager from '@ohos.backgroundTaskManager';

backgroundTaskManager.backgroundTaskManager.resetAllEfficiencyResources();

Development Examples

import backgroundTaskManager from '@ohos.backgroundTaskManager';

// Apply for efficiency resources.
let request = {
    resourceTypes: backgroundTaskManager.ResourceType.COMMON_EVENT|
        backgroundTaskManager.ResourceType.TIMER,
    isApply: true,
    timeOut: 0,
    reason: "apply",
    isPersist: true,
    isProcess: true,
};
let res = backgroundTaskManager.applyEfficiencyResources(request);
console.info("the result of request is: " + res);

// Release some efficiency resources.
request = {
    resourceTypes: backgroundTaskManager.ResourceType.COMMON_EVENT,
    isApply: false,
    timeOut: 0,
    reason: "reset",
};
res = backgroundTaskManager.applyEfficiencyResources(request);
console.info("the result of request is: " + res);

// Release all efficiency resources.
backgroundTaskManager.backgroundTaskManager.resetAllEfficiencyResources();

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