AbilityStage is a Module-level component manager. When the application HAP is loaded for the first time, an AbilityStage instance is created, which can be used to initialize the Module. AbilityStage corresponds to HAP on a one-to-one basis, that is, each HAP has one AbilityStage instance.
AbilityStage has the lifecycle callbacks onCreate() and onDestroy() and the event callbacks onAcceptWant(), onConfigurationUpdate(), onMemoryLevel(), onNewProcessRequest(), and onPrepareTermination().
onCreate() lifecycle callback: Before the first application component (such as the UIAbility or the ExtensionAbility) instance of the corresponding module is loaded, an AbilityStage instance is created. This callback is invoked when the AbilityStage instance is created. The AbilityStage module notifies you of when you can perform module initialization such as resource pre-loading and thread creation during module loading.
onAcceptWant() event callback: triggered when UIAbility is started in the specified mode. For details, see UIAbility Launch Type Overview.
onConfigurationUpdate() event callback: triggered when a system environment variable changes. The system environment variables, such as the system language and theme, are defined in the Configuration class before project configuration.
onMemoryLevel() event callback: triggered when the system adjusts the memory. When an application is switched to the background, it is cached in the background. This adversely affects the overall system performance. When system resources are insufficient, the system reclaims memory from applications in multiple ways. For example, the system may stop applications to release memory for executing key tasks. To further maintain the balance of the system memory and prevent the system from stopping application processes, you can subscribe to the system memory changes in the onMemoryLevel() lifecycle callback of AbilityStage to release unnecessary resources.
onNewProcessRequest() event callback: triggered when the UIAbility is started. You can use this callback to specify whether each UIAbility should be created in a separate process. The callback returns a custom string identifier. If the returned string matches an existing identifier, the corresponding process is reused; otherwise, a new process is created. Note that this callback must be used in conjunction with the isolationProcess field set to true in the module.json5 file.
onPrepareTermination() event callback: triggered when the application is closed by the user, allowing the user to choose between immediate termination or cancellation. You can notify the system whether to continue with the shutdown action by returning an enumerated value defined in AbilityConstant.PrepareTermination within the callback.
onDestroy() lifecycle callback: triggered when the last Ability instance of the corresponding module exits. This callback is triggered only when the application is destroyed normally. It is not triggered if the application exits abnormally or is terminated.
AbilityStage is not automatically generated in the default project of DevEco Studio. To use AbilityStage, you can manually create an AbilityStage file. The procedure is as follows:
In the ets directory of the Module project, right-click and choose New > Directory to create a directory named exampleabilitystage.
In the exampleabilitystage directory, right-click and choose New > ArkTS File to create a file named MyAbilityStage.ets.
Open the MyAbilityStage.ets file, and import the dependency package of AbilityStage. Customize a class that inherits from AbilityStage, and add the required lifecycle callbacks. The following code snippet adds the onCreate() lifecycle callback.
import { AbilityStage, Want } from '@kit.AbilityKit';
export default class MyAbilityStage extends AbilityStage {
onCreate(): void {
// This callback is triggered when the HAP is loaded for the first time. In this callback, you can initialize the module (for example, pre-load resources and create threads).
}
onAcceptWant(want: Want): string {
// Triggered only for the UIAbility with the specified launch type.
return 'MyAbilityStage';
}
} In the module.json5 file, set srcEntry to specify the code path of the module as the entry for loading the HAP.
{
"module": {
"name": "entry",
"type": "entry",
"srcEntry": "./ets/myabilitystage/MyAbilityStage.ets",
// ···
}
} Here is an example of how to use the callback functions of the AbilityStage component to track changes in system environment variables.
In the onCreate() lifecycle, use EnvironmentCallback to listen for system environment changes, such as the system language, light/dark mode, screen orientation, font size scaling factor, and font weight scaling factor.
When a system environment variable changes, the onConfigurationUpdated() callback in EnvironmentCallback is triggered and related information is logged.
When the application process is terminated, the onDestroy() callback of the AbilityStage component is triggered.
import { EnvironmentCallback, AbilityStage } from '@kit.AbilityKit';
import { BusinessError } from '@kit.BasicServicesKit';
export default class MyAbilityStage extends AbilityStage {
onCreate(): void {
console.info('AbilityStage onCreate');
let envCallback: EnvironmentCallback = {
onConfigurationUpdated(config) {
console.info(`envCallback onConfigurationUpdated success: ${JSON.stringify(config)}`);
let language = config.language; // Current language of the application.
let colorMode = config.colorMode; // Dark/light color mode.
let direction = config.direction; // Screen orientation.
let fontSizeScale = config.fontSizeScale; // Font size scale.
let fontWeightScale = config.fontWeightScale; // Font weight scale.
},
onMemoryLevel(level) {
console.info(`onMemoryLevel level: ${level}`);
}
};
try {
let applicationContext = this.context.getApplicationContext();
let callbackId = applicationContext.on('environment', envCallback);
console.info(`callbackId: ${callbackId}`);
} catch (paramError) {
console.error(`error: ${(paramError as BusinessError).code}, ${(paramError as BusinessError).message}`);
}
}
onDestroy(): void {
// Use onDestroy() to listen for the ability destruction event.
console.info('AbilityStage onDestroy');
}
}