xref: /docs/zh-cn/application-dev/reference/apis-ability-kit/js-apis-app-ability-applicationStateChangeCallback.md

# @ohos.app.ability.ApplicationStateChangeCallback (ApplicationStateChangeCallback)

ApplicationStateChangeCallback模块提供应用上下文ApplicationContext对当前应用前后台变化监听回调的能力。

> **说明：**
>
> 本模块首批接口从API version 10 开始支持。后续版本的新增接口，采用上角标单独标记接口的起始版本。
>
> 本模块接口仅可在Stage模型下使用。

## 导入模块

```ts
import { ApplicationStateChangeCallback } from '@kit.AbilityKit';
```

## ApplicationStateChangeCallback.onApplicationForeground

onApplicationForeground(): void

注册当前应用前后台变化的监听后，在当前应用从后台切换到前台时触发回调。

**原子化服务API：** 从API version 11开始，该接口支持在原子化服务中使用。

**系统能力**：SystemCapability.Ability.AbilityRuntime.AbilityCore

**示例：**

参见[onApplicationBackground](#applicationstatechangecallbackonapplicationbackground)。

## ApplicationStateChangeCallback.onApplicationBackground

onApplicationBackground(): void

注册当前应用前后台变化的监听后，在当前应用从前台切换到后台时触发回调。

**原子化服务API：** 从API version 11开始，该接口支持在原子化服务中使用。

**系统能力**：SystemCapability.Ability.AbilityRuntime.AbilityCore

**示例：**

```ts
import { UIAbility, ApplicationStateChangeCallback } from '@kit.AbilityKit';
import { BusinessError } from '@kit.BasicServicesKit';

let applicationStateChangeCallback: ApplicationStateChangeCallback = {
  onApplicationForeground() {
    console.info('applicationStateChangeCallback onApplicationForeground');
  },
  onApplicationBackground() {
    console.info('applicationStateChangeCallback onApplicationBackground');
  }
};

export default class MyAbility extends UIAbility {
  onCreate() {
    console.log('MyAbility onCreate');
    // 1.获取applicationContext
    let applicationContext = this.context.getApplicationContext();
    try {
      // 2.通过applicationContext注册应用前后台状态监听
      if (applicationContext != undefined) {
        applicationContext.on('applicationStateChange', applicationStateChangeCallback);
      }
    } catch (paramError) {
      console.error(`error: ${(paramError as BusinessError).code}, ${(paramError as BusinessError).message}`);
    }
    console.log('Resgiter applicationStateChangeCallback');
  }
  onDestroy() {
    let applicationContext = this.context.getApplicationContext();
    try {
      // 1.通过applicationContext解除注册应用前后台状态监听
      if (applicationContext != undefined) {
        applicationContext.off('applicationStateChange', applicationStateChangeCallback);
      } 
    } catch (paramError) {
      console.error(`error: ${(paramError as BusinessError).code}, ${(paramError as BusinessError).message}`);
    }
  }
}
```