1# Subscribing to Common Events in Static Mode (for System Applications Only)
2
3## When to Use
4
5A static subscriber is started once it receives a target event published by the system or application. At the same time, [onReceiveEvent()](../../reference/apis-basic-services-kit/js-apis-application-staticSubscriberExtensionAbility-sys.md#staticsubscriberextensionabilityonreceiveevent) is triggered, in which you can implement the service logic.
6
7For 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.
8
9Subscribing to a common event in static mode is achieved by configuring a declaration file and implementing a class that inherits from [StaticSubscriberExtensionAbility](../../reference/apis-basic-services-kit/js-apis-application-staticSubscriberExtensionAbility-sys.md).
10
11> **NOTE**
12>
13> The static subscription mode has negative impact on system power consumption. Therefore, exercise caution when using this mode.
14
15## How to Develop
16
171. Declaring a static subscriber.
18
19   To declare a static subscriber, create an ExtensionAbility, which is derived from the **StaticSubscriberExtensionAbility** class, in the project.
20
21   You can implement service logic using [`onReceiveEvent()`](../../reference/apis-basic-services-kit/js-apis-application-staticSubscriberExtensionAbility-sys.md#staticsubscriberextensionabilityonreceiveevent).
22
23   ```ts
24   import { commonEventManager, StaticSubscriberExtensionAbility } from '@kit.BasicServicesKit';
25   import { hilog } from '@kit.PerformanceAnalysisKit';
26
27   const TAG: string = 'StaticSubscriber';
28   const DOMAIN_NUMBER: number = 0xFF00;
29
30   export default class StaticSubscriber extends StaticSubscriberExtensionAbility {
31     onReceiveEvent(event: commonEventManager.CommonEventData): void {
32       hilog.info(DOMAIN_NUMBER, TAG, 'onReceiveEvent, event: ' + event.event);
33       //...
34     }
35   }
36   ```
37
382. Configure static subscriber settings.
39
40   After writing the static subscriber code, configure the subscriber in the [module.json5](../../quick-start/module-configuration-file.md) file.
41
42   ```json
43   {
44     "module": {
45   	// ...
46       "extensionAbilities": [
47         {
48           "name": "StaticSubscriber",
49           "srcEntry": "./ets/staticsubscriber/StaticSubscriber.ets",
50           "description": "$string:StaticSubscriber_desc",
51           "icon": "$media:app_icon",
52           "label": "$string:StaticSubscriber_label",
53           "type": "staticSubscriber",
54           "exported": false,
55           "metadata": [
56             {
57               "name": "ohos.extension.staticSubscriber",
58               "resource": "$profile:staticsubscriber"
59             }
60           ]
61         }
62       ],
63   	// ...
64     }
65   }
66   ```
67
68   Some fields in the file are described as follows:
69
70   - **srcEntry**: entry file path of the ExtensionAbility, that is, the file path of the static subscriber declared in Step 2.
71
72   - **type**: ExtensionAbility type. For a static subscriber, set this field to **staticSubscriber**.
73
74   - **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.
75        - **name**: name of the ExtensionAbility. For a static subscriber, declare the name as **ohos.extension.staticSubscriber** for successful identification.
76        - **resource**: path that stores the ExtensionAbility configuration, which is customizable. In this example, the path is **resources/base/profile/subscribe.json**.
77
78
793. Configure the level-2 configuration file to which the metadata points.
80
81   ```json
82   {
83     "commonEvents": [
84       {
85         "name": "StaticSubscriber",
86         "permission": "",
87         "events": [
88           "usual.event.AIRPLANE_MODE"
89         ]
90       }
91     ]
92   }
93   ```
94
95   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:
96
97   - **name**: name of the ExtensionAbility, which must be the same as the name of **extensionAbility** declared in **module.json5**.
98   - **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.
99   - **events**: list of target events to subscribe to.
100
1014. Modify the [preset configuration file](https://gitee.com/openharmony/vendor_hihope/blob/master/rk3568/preinstall-config/install_list_capability.json) of the device, that is, the **/system/variant/phone/base/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:
102
103   - **bundleName**: bundle name of the application.
104   - **app_signature**: fingerprint information of the application. For details about how to configure fingerprint information, see [Application Privilege Configuration](https://gitee.com/openharmony/docs/blob/master/en/device-dev/subsystems/subsys-app-privilege-config-guide.md#configuration-in-install_list_capabilityjson), or obtain and enter the application ID using [Bundle Manager](https://gitee.com/openharmony/docs/blob/master/en/application-dev/tools/bm-tool.md).
105   - **allowCommonEvent**: type of common event that can be started by static broadcast.
106
107   ```json
108   [
109     // ...
110     {
111       "bundleName": "com.samples.stageprocessthread", // Bundle name.
112       "app_signature": ["****"], // Fingerprint information.
113       "allowCommonEvent": ["usual.event.AIRPLANE_MODE"] // Type of common event that can be started by static broadcast.
114     }
115   ]
116   ```
117
118   > **NOTE**
119   >
120   > The **install_list_capability.json** file is available only for preinstalled applications.
121
122