Ability continuation is to continue the current mission of an application, including the UI component status variables and distributed objects, on another device. The UI component status variables are used to synchronize page data, and the distributed objects are used to synchronize data in the memory.
## Available APIs
The following table lists the APIs used for ability continuation. For details about the APIs, see [Ability](https://gitee.com/openharmony/docs/blob/master/en/application-dev/reference/apis/js-apis-application-ability.md).
**Table 1** Ability continuation APIs
|API| Description|
|:------ | :------|
| onContinue(wantParam : {[key: string]: any}): OnContinueResult | Called by the **initiator** to save data during the ability continuation preparation process. The return value **0** means that the continuation request is accepted, and an error code means that the continuation request is denied.|
| onCreate(want: Want, param: LaunchParam): void| Called by the **target** to restore the data and page.|
| **enum** OnContinueResult | Enumerates the return values of **onContinue**. The options are as follows: **AGREE** (request accepted), **REJECT** (request denied), and **MISMATCH** (version mismatch).|
- Configure the application to support ability continuation.
Set the **continuable** field in the **module.json5** file to **true**. The default value is **false**. If this parameter is set to **false**, the application cannot be continued on another device.
```javascript
"continuable":true
```
* Configure the application startup type.
Set **launchType** in the **module.json5** to **standard**. Currently, only multi-instance applications can be continued on another device.
```javascript
"launchType":"standard"
```
* Apply for the distributed permissions.
Declare the **DISTRIBUTED_DATASYNC** permission in the **module.json5** file for the application.
```javascript
"requestPermissions":[
{
"name":"ohos.permission.DISTRIBUTED_DATASYNC"
},
```
This permission must be granted by the user in a dialog box when the application is started for the first time. To enable the application to display a dialog box to ask for the permission, add the following code to **onWindowStageCreate** of the **Ability** class:
The **onContinue** API is called by the **initiator** to save the UI component status variables and memory data and prepare for continuation. After the application completes the continuation preparation, the system must return **OnContinueResult.AGREE** to accept the continuation request. If an error code is returned, the request is denied. If this API is not implemented, the system rejects the continuation request by default.
3. Implement the continuation logic in the **onCreate** API.
The **onCreate** API is called by the **target**. When the ability is started on the target device, this API is called to instruct the application to synchronize the memory data and UI component status, and triggers page restoration after the synchronization is complete. If the continuation logic is not implemented, the ability will be started in common startup mode and the page cannot be restored.
- The target device determines whether the startup is **LaunchReason.CONTINUATION** based on **launchReason** in **onCreate**.
- After data restore is complete, call **restoreWindowStage** to trigger page restoration.
Distributed data objects allow cross-device data synchronization like local variables. For two devices that form a Super Device, when data in the distributed data object of an application is added, deleted, or modified on a device, the data for the same application is also updated on the other device. Both devices can listen for the data changes and online and offline states of the other. For details, see [Distributed Data Object Development](https://gitee.com/openharmony/docs/blob/master/en/application-dev/database/database-distributedobject-guidelines.md).
In the ability continuation scenario, the distributed data object is used to synchronize the memory data from the local device to the target device.
- In **onContinue**, the initiator saves the data to be continued to the distributed object, sets the session ID, and sends the session ID to the target device through **wantParam**.
```javascript
import Ability from '@ohos.application.Ability';
import distributedObject from '@ohos.data.distributedDataObject';
var g_object = distributedObject.createDistributedObject({name:undefined});
export default class MainAbility extends Ability {
// Set the session ID for the distributed data object.
g_object.setSessionId(this.sessionId);
g_object.name = "Amy";
// Set the session ID into the want parameter.
wantParam["session"] = this.sessionId;
return AbilityConstant.OnContinueResult.AGREE
}
```
- The target device obtains the session ID from **onCreate**, creates a distributed object, and associates the distributed object with the session ID. In this way, the distributed object can be synchronized. Before calling **restoreWindowStage**, ensure that all distributed objects required for continuation have been associated for correct data retrieval.
