# FenceExtensionAbility

## Overview
[FenceExtensionAbility](../reference/apis-location-kit/js-apis-app-ability-FenceExtensionAbility.md) is an ExtensionAbility of the geofence type. It enables you to efficiently implement geofencing functionalities.

## How to Use

1. Subscribe to geofence status change events through the [geoLocationManager.on('gnssFenceStatusChange')](../reference/apis-location-kit/js-apis-geoLocationManager.md#geolocationmanagerongnssfencestatuschange) API of the location service, and pass the FenceExtensionAbility parameters in the **want** parameter.
2. After the event is triggered, the system reports the geofence event and data through the **onFenceStatusChange** API. Based on the event received, the application can perform corresponding service processing, for example, sending notifications.

## Available APIs
For details about the APIs, see [FenceExtensionAbility](../reference/apis-location-kit/js-apis-app-ability-FenceExtensionAbility.md).
| API| Description|
| ---- | ---- |
| onFenceStatusChange(transition: geoLocationManager.GeofenceTransition, additions: Record<string, string>): void  | Callback invoked when a geofence status change event is received. Service processing is then performed based on the event type and data.|
| onDestroy(): void | Callback invoked when a FenceExtensionAbility destruction event is received.|

## How to Develop

### Implementing a FenceExtensionAbility

Implement the capability of the [FenceExtensionAbility](../reference/apis-location-kit/js-apis-app-ability-FenceExtensionAbility.md) provider.

To manually create a FenceExtensionAbility in a project in DevEco Studio, perform the following steps:

1. In the **ets** directory of a module in the project, right-click and choose **New > Directory** to create a directory named **fenceextensionability**.
2. Right-click the **fenceextensionability** directory, and choose **New > File** to create a file named **MyFenceExtensionAbility.ets**.
3. Open the **MyFenceExtensionAbility.ets** file and import its dependencies. Customize a class that inherits from **FenceExtensionAbility** and implement the **onFenceStatusChange** and **onDestroy** APIs.

   The code snippet is as follows:

   ```ts
   import { notificationManager } from '@kit.NotificationKit';
   import { wantAgent } from '@kit.AbilityKit';
   import { FenceExtensionAbility, geoLocationManager } from '@kit.LocationKit';
   
   export default class MyFenceExtensionAbility extends FenceExtensionAbility {
     async onFenceStatusChange(transition: geoLocationManager.GeofenceTransition,
       additions: Record<string, string>): Promise<void> {
       // Receive the geofence status change event and process the service logic.
       console.log(`on geofence transition,id:${transition.geofenceId},event:${transition.transitionEvent},additions:${JSON.stringify(additions)}`);
   
       // Send a geofence notification.
       let wantAgentInfo: wantAgent.WantAgentInfo = {
         wants: [
           {
             bundleName: 'com.example.myapplication',
             abilityName: 'EntryAbility',
             parameters:
             {
               "geofenceId": transition?.geofenceId,
               "transitionEvent": transition?.transitionEvent,
             }
           } as Want
         ],
         actionType: wantAgent.OperationType.START_ABILITY,
         requestCode: 100
       };
       let wantAgentMy = await wantAgent.getWantAgent(wantAgentInfo);
       let notificationRequest: notificationManager.NotificationRequest = {
         id: 1,
         content: {
           notificationContentType: notificationManager.ContentType.NOTIFICATION_CONTENT_BASIC_TEXT,
           normal: {
             title: `Geofence Notification`,
             text: `on geofence transition,id:${transition.geofenceId},event:${transition.transitionEvent},additions:${JSON.stringify(additions)}`,
           }
         },
         notificationSlotType: notificationManager.SlotType.SOCIAL_COMMUNICATION,
         wantAgent: wantAgentMy
       };
       notificationManager.publish(notificationRequest);
     }
   
     onDestroy(): void {
       // Process the FenceExtensionAbility destruction event.
       console.log(`on ability destroy`);
     }
   }
   export default MyFenceExtensionAbility;
   ```

4. Register the FenceExtensionAbility in the [module.json5 file](../quick-start/module-configuration-file.md) of the module in the project. Set **type** to **"fence"** and **srcEntry** to the code path of the FenceExtensionAbility component.

    ```json
    {
      "module": {
        "extensionAbilities": [
          {
            "name": "MyFenceExtensionAbility",
            "srcEntry": "./ets/fenceExtensionability/MyFenceExtensionAbility.ets",
            "description": "MyFenceExtensionAbility",
            "type": "fence",
            "exported": true
          },
        ]
      }
    }
    ```