UIAbility Backup and Restore

When to Use

When an application runs in the background, factors such as system resource control may cause the application to close or its process to terminate, which might result in the loss of user data. However, if the application has enabled the UIAbility backup and restore feature within UIAbilityContext and saved temporary data, it can restore the previous state and data (including the page stack and the data stored in the onSaveState callback) when it restarts after being closed, maintaining a seamless user experience.

NOTE

If the application is stopped normally, the UIAbility backup process is not triggered. If the application is started normally (for example, by calling the startAbility API or clicking the icon), the UIAbility restore process is not triggered.

Working Mechanism

• UIAbility data backup: After an application transitions to the onBackground lifecycle, the system automatically calls onSaveState to back up data.
• UIAbility data restore: The restored Want data can be obtained from the onCreate lifecycle of the application, and the page stack data can be restored in the onWindowStageCreate lifecycle of the application.

Constraints

• The UIAbility backup and restore feature supports multiple instances. Backup data is stored in the application sandbox path as files for seven days.

• Backup data is stored in the parameter field of Want. Due to serialization constraints, the maximum data volume supported is 200 KB.

• Data restore is unavailable after device restart.

• The data backup and restore feature is unavailable for a UIExtensionAbility.

Available APIs

The UIAbility backup and restore API is provided by the UIAbilityContext module. You can directly use this.context in the UIAbility to call them. For details, see How to Develop.

setRestoreEnabled must be called during application initialization (before onForeground is invoked). For example, it can be called in the onCreate callback of the UIAbility.

How to Develop

To enable UIAbility backup and restore during application module initialization, refer to the code snippet below.

import { AbilityConstant, UIAbility, Want } from '@kit.AbilityKit';
import { hilog } from '@kit.PerformanceAnalysisKit';
// ···

const DOMAIN = 0x0000;

export default class EntryAbility extends UIAbility {
  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    hilog.info(DOMAIN, 'EntryAbility', '[Demo] EntryAbility onCreate');
    this.context.setRestoreEnabled(true);
    // ···
  }

// ···
}

To proactively save data and restore the data when the UIAbility is started, refer to the code snippet below.

import { AbilityConstant, UIAbility, Want } from '@kit.AbilityKit';
import { hilog } from '@kit.PerformanceAnalysisKit';
// ···

const DOMAIN = 0x0000;

export default class EntryAbility extends UIAbility {
  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    hilog.info(DOMAIN, 'EntryAbility', '[Demo] EntryAbility onCreate');
    this.context.setRestoreEnabled(true);
    if (want && want.parameters) {
      let recoveryMyData = want.parameters['myData'];
    }
  }

  onSaveState(reason: AbilityConstant.StateType, wantParam: Record<string, Object>): AbilityConstant.OnSaveResult {
    // Save the application data.
    hilog.info(DOMAIN, 'EntryAbility', '[Demo] EntryAbility onSaveState');
    wantParam['myData'] = 'my1234567';
    return AbilityConstant.OnSaveResult.ALL_AGREE;
  }

// ···
}