1# @ohos.app.ability.EnvironmentCallback (EnvironmentCallback) 2 3The **EnvironmentCallback** module provides APIs for the application context to listen for system environment changes. 4 5> **NOTE** 6> 7> The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version. 8> The APIs of this module can be used only in the stage model. 9 10 11## Modules to Import 12 13```ts 14import EnvironmentCallback from '@ohos.app.ability.EnvironmentCallback'; 15``` 16 17 18## EnvironmentCallback.onConfigurationUpdated 19 20onConfigurationUpdated(config: Configuration): void; 21 22Called when the system environment changes. 23 24**System capability**: SystemCapability.Ability.AbilityRuntime.AbilityCore 25 26**Parameters** 27 28 | Name| Type| Mandatory| Description| 29 | -------- | -------- | -------- | -------- | 30 | config | [Configuration](js-apis-app-ability-configuration.md) | Yes| **Configuration** object after the change.| 31 32## EnvironmentCallback.onMemoryLevel 33 34onMemoryLevel(level: AbilityConstant.MemoryLevel): void; 35 36Called when the system memory level changes. 37 38**System capability**: SystemCapability.Ability.AbilityRuntime.AbilityCore 39 40**Parameters** 41 42 | Name| Type| Mandatory| Description| 43 | -------- | -------- | -------- | -------- | 44 | level | [AbilityConstant.MemoryLevel](js-apis-app-ability-abilityConstant.md#abilityconstantmemorylevel) | Yes| Memory level that indicates the memory usage status. When the specified memory level is reached, a callback will be invoked and the system will start adjustment.| 45 46**Example** 47 48```ts 49import UIAbility from '@ohos.app.ability.UIAbility'; 50import EnvironmentCallback from '@ohos.app.ability.EnvironmentCallback'; 51 52let callbackId: number; 53 54export default class MyAbility extends UIAbility { 55 onCreate() { 56 console.log('MyAbility onCreate'); 57 let environmentCallback: EnvironmentCallback = { 58 onConfigurationUpdated(config){ 59 console.log(`onConfigurationUpdated config: ${JSON.stringify(config)}`); 60 }, 61 62 onMemoryLevel(level){ 63 console.log(`onMemoryLevel level: ${JSON.stringify(level)}`); 64 } 65 }; 66 // 1. Obtain an applicationContext object. 67 let applicationContext = this.context.getApplicationContext(); 68 // 2. Register a listener for the environment changes through the applicationContext object. 69 callbackId = applicationContext.on('environment', environmentCallback); 70 console.log(`registerEnvironmentCallback number: ${JSON.stringify(callbackId)}`); 71 } 72 onDestroy() { 73 let applicationContext = this.context.getApplicationContext(); 74 applicationContext.off('environment', callbackId, (error, data) => { 75 if (error && error.code !== 0) { 76 console.error(`unregisterEnvironmentCallback fail, error: ${JSON.stringify(error)}`); 77 } else { 78 console.log(`unregisterEnvironmentCallback success, data: ${JSON.stringify(data)}`); 79 } 80 }); 81 } 82} 83``` 84