# AccessibilityExtensionAbility Development

The **AccessibilityExtensionAbility** module provides accessibility extension capabilities based on the **ExtensionAbility** framework. You can develop your accessibility applications by applying the **AccessibilityExtensionAbility** template to enhance usability.

> **Environment Requirements**
>
> IDE: DevEco Studio 3.0 Beta3 (3.0.0.900) or later
>
> SDK: API version 9 or later
>
> Model: stage

This document is organized as follows:

- [AccessibilityExtensionAbility Development](#accessibilityextensionability-development)
  - [Creating an Accessibility Extension Service](#creating-an-accessibility-extension-service)
    - [Creating a Project](#creating-a-project)
    - [Creating an AccessibilityExtAbility File](#creating-an-accessibilityextability-file)
  - [Processing an Accessibility Event](#processing-an-accessibility-event)
  - [Declaring Capabilities of Accessibility Extension Services](#declaring-capabilities-of-accessibility-extension-services)
  - [Enabling a Custom Accessibility Extension Service](#enabling-a-custom-accessibility-extension-service)

## Creating an Accessibility Extension Service

You can create an accessibility extension service by creating a project from scratch or adding the service to an existing project.

### Creating a Project

Perform the following steps in DevEco Studio:
1. From the upper left corner of DevEco Studio, choose **File** > **New** > **Create Project**.
2. By following the project creation wizard, click the **OpenHarmony** tab, select the **Empty Ability** template, and then click **Next**.
3. Set **Project type** to **Application**, **Compile API** (or **Compile SDK**, depending on the version used) to **9**, and **Model** to **Stage**, and then click **Finish**.

### Creating an AccessibilityExtAbility File

To add an accessibility extension service to a project, create the **AccessibilityExtAbility** folder in the **ets** folder of the project, create the **AccessibilityExtAbility.ts** file in the new folder, and add the following code to the new file:

```typescript
import AccessibilityExtensionAbility from '@ohos.application.AccessibilityExtensionAbility';

class AccessibilityExtAbility extends AccessibilityExtensionAbility {
    onConnect() {
        console.log('AccessibilityExtAbility onConnect');
    }

    onDisconnect() {
        console.log('AccessibilityExtAbility onDisconnect');
    }

    onAccessibilityEvent(accessibilityEvent) {
        console.log('AccessibilityExtAbility onAccessibilityEvent: ' + JSON.stringify(accessibilityEvent));
    }
}

export default AccessibilityExtAbility;
```

The APIs defined in the file are as follows.

| API| Description|
| ---- | ---- |
| onConnect(): void | Called when a connection with the extension service is set up.|
| onDisconnect(): void | Called when the connection with the extension service is severed.|
| onAccessibilityEvent(event: AccessibilityEvent): void | Called when an accessibility event occurs|

## Processing an Accessibility Event

You can process the service logic for accessibility events in the **onAccessibilityEvent()** API. For details about the events, see [AccessibilityEvent](../reference/apis/js-apis-application-accessibilityExtensionAbility.md#accessibilityevent). The following code snippet uses the **pageStateUpdate** event as an example.

```typescript
onAccessibilityEvent(accessibilityEvent) {
    console.log('AccessibilityExtAbility onAccessibilityEvent: ' + JSON.stringify(accessibilityEvent));
    if (accessibilityEvent.eventType === 'pageStateUpdate') {
        console.log('AccessibilityExtAbility onAccessibilityEvent: pageStateUpdate');
        // TODO: Develop custom logic.
    }
}
```
For an accessibility event, you can use the APIs of the [AccessibilityExtensionContext](../reference/apis/js-apis-inner-application-accessibilityExtensionContext.md) module to configure the concerned information, obtain root information, and inject gestures.

You can also process physical key events in the accessibility extension service. For details, see [onKeyEvent](../reference/apis/js-apis-application-accessibilityExtensionAbility.md#accessibilityextensionabilityonkeyevent).

## Declaring Capabilities of Accessibility Extension Services

After developing the custom logic for an accessibility extension service, you must add the configuration information of the service to the corresponding module-level **module.json5** file in the project directory. In the file, the **srcEntry** tag indicates the path to the accessibility extension service. Make sure the value of the **type** tag is fixed at **accessibility**. Otherwise, the connection to the service will fail.

```json
"extensionAbilities": [
  {
    "name": "AccessibilityExtAbility",
    "srcEntry": "./ets/AccessibilityExtAbility/AccessibilityExtAbility.ts",
    "label": "$string:MainAbility_label",
    "description": "$string:MainAbility_desc",
    "type": "accessibility",
    "metadata": [
      {
        "name": "ohos.accessibleability",
        "resource": "$profile:accessibility_config"
      }
    ]
  }
]
```
**accessibility_config** is the specific configuration of the accessibility extension service. You need to create the **accessibility_config.json** file in **resources/base/profile/** and declare the [capabilities](../reference/apis/js-apis-accessibility.md#capability) of the service in the file.
```json
{
  "accessibilityCapabilities": [
    "retrieve",
    "gesture"
  ]
}
```
## Enabling a Custom Accessibility Extension Service

To enable or disable an accessibility extension service, run the following command:
- To enable the service: **accessibility enable -a AccessibilityExtAbility -b com.example.demo -c rg**
- To disable the service: **accessibility disable -a AccessibilityExtAbility -b com.example.demo**

In the preceding commands, **AccessibilityExtAbility** indicates the name of the accessibility extension service, **com.example.demo** indicates the bundle name, and **rg** indicates the capabilities (**r** is short for retrieve).

If the service is enabled or disabled successfully, the message "enable ability successfully" or "disable ability successfully" is displayed.