harmony 鸿蒙Subscribing to Common Events in Static Mode (for System Applications Only)

2023-06-24
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Subscribing to Common Events in Static Mode (for System Applications Only)

When to Use

A static subscriber is started once it receives a target event published by the system or application. At the same time, the onReceiveEvent() callback is triggered, in which you can implement the service logic. For example, if an application needs to execute some initialization tasks during device power-on, the application can subscribe to the power-on event in static mode. After receiving the power-on event, the application is started to execute the initialization tasks.

Subscribing to a common event in static mode is achieved by configuring a declaration file and implementing a class that inherits from StaticSubscriberExtensionAbility.

NOTE

The static subscription mode has negative impact on system power consumption. Therefore, exercise caution when using this mode.

How to Develop

Declaring a static subscriber.

To declare a static subscriber, create an ExtensionAbility, which is derived from the StaticSubscriberExtensionAbility class, in the project.

You can implement service logic in the onReceiveEvent() callback.

   import StaticSubscriberExtensionAbility from '@ohos.application.StaticSubscriberExtensionAbility';
   import commonEventManager from '@ohos.commonEventManager';
   
   export default class StaticSubscriber extends StaticSubscriberExtensionAbility {
     onReceiveEvent(event: commonEventManager.CommonEventData) {
       console.info('onReceiveEvent, event: ' + event.event);
     }
   }

Configure static subscriber settings.

After writing the static subscriber code, configure the subscriber in the module.json5 file.

   {
     "module": {
       "extensionAbilities": [
         {
           "name": "StaticSubscriber",
           "srcEntry": "./ets/staticsubscriber/StaticSubscriber.ts",
           "description": "$string:StaticSubscriber_desc",
           "icon": "$media:icon",
           "label": "$string:StaticSubscriber_label",
           "type": "staticSubscriber",
           "exported": true,
           "metadata": [
             {
               "name": "ohos.extension.staticSubscriber",
               "resource": "$profile:subscribe"
             }
           ]
         }
       ]
     }
   }

Some fields in the file are described as follows:

**srcEntry **: entry file path of the ExtensionAbility, that is, the file path of the static subscriber declared in Step 2.
type: ExtensionAbility type. For a static subscriber, set this field to staticSubscriber.
metadata: level-2 configuration file information of the ExtensionAbility. The configuration information varies according to the ExtensionAbility type. Therefore, you must use different config files to indicate the specific configuration. - name: name of the ExtensionAbility. For a static subscriber, declare the name as ohos.extension.staticSubscriber for successful identification. - resource: path that stores the ExtensionAbility configuration, which is customizable. In this example, the path is resources/base/profile/subscribe.json.
Configure the level-2 configuration file to which the metadata points.

   {
     "commonEvents": [
       {
         "name": "xxx",
         "permission": "xxx",
         "events":[
           "xxx"
         ]
       }
     ]
   }

If the level-2 configuration file is not declared in this format, the file cannot be identified. Some fields in the file are described as follows:

name: name of the ExtensionAbility, which must be the same as the name of extensionAbility declared in module.json5.
permission: permission required for the publisher. If a publisher without the required permission attempts to publish an event, the event is regarded as invalid and will not be published.
events: list of target events to subscribe to.
Modify the preset configuration file of the device, that is, the /system/etc/app/install_list_capability.json file on the device. When the device is started, this file is read. During application installation, the common event type specified by allowCommonEvent in the file is authorized. The install_list_capability.json file contains the following fields:
- bundleName: bundle name of the application.
- app_signature: fingerprint information of the application. For details, see Configuration in install_list_capability.json.
- allowCommonEvent: type of common event that can be started by static broadcast.

   [
     ...
     {
       "bundleName": "com.example.myapplication", // Bundle name.
       "app_signature": ["****"], // Fingerprint information.
       "allowCommonEvent": ["usual.event.A", "usual.event.B"] // Type of common event that can be started by static broadcast.
     }
   ]