1# AbilityForegroundStateObserver 2 3The **AbilityForegroundStateObserver** module defines the listener used to listen for ability foreground and background state changes. 4 5> **NOTE** 6> 7> The initial APIs of this module are supported since API version 11. Newly added APIs will be marked with a superscript to indicate their earliest API version. 8> The APIs provided by this module are system APIs. 9 10## Modules to Import 11 12```ts 13import abilityManager from '@ohos.app.ability.abilityManager'; 14``` 15 16## Attributes 17 18**System capability**: SystemCapability.Ability.AbilityRuntime.Core 19 20| Name | Type | Readable| Writable| Description | 21| -------------------------------- | ---------------------- | ---- | ---- | ------------------ | 22| onAbilityStateChanged | AsyncCallback\<void> | Yes | No | Callback invoked when the foreground or background state of an ability changes. The parameter type passed in is [AbilityStateData](js-apis-inner-application-appStateData.md).| 23 24**Example** 25```ts 26import abilityManager from '@ohos.app.ability.abilityManager'; 27import { BusinessError } from '@ohos.base'; 28 29let observer: abilityManager.AbilityForegroundStateObserver = { 30 onAbilityStateChanged(abilityStateData) { 31 console.log(`onAbilityStateChanged: ${JSON.stringify(abilityStateData)}`); 32 }, 33}; 34try { 35 abilityManager.on('abilityForegroundState', observer); 36} catch (paramError) { 37 let code = (paramError as BusinessError).code; 38 let message = (paramError as BusinessError).message; 39 console.error(`error: ${code}, ${message} `); 40} 41``` 42