HarmonyOS鸿蒙Next中切换深色模式后，重启应用，设置丢失

可以用首选项进行模式更改后的保存

//index.ets
```javascript
import { common, ConfigurationConstant } from '[@kit](/user/kit).AbilityKit';
import preferences from '[@ohos](/user/ohos).data.preferences';
import dataPreferences from '[@ohos](/user/ohos).data.preferences';
import { BusinessError } from '[@kit](/user/kit).BasicServicesKit';

[@Entry](/user/Entry)
[@Component](/user/Component)
struct Index {
  [@State](/user/State) message: string = 'Hello World';
  [@State](/user/State) flag:boolean=false
  build() {
    RelativeContainer() {
      Button('点击').onClick(() => {
        let options: preferences.Options = { name: 'myStore' };
        let context = getContext(this) as common.Context;
        let dataPreferences = preferences.getPreferencesSync(context, options);
        let value: preferences.ValueType = dataPreferences.getSync('color', false);
        console.log(value+'7667676')
      })
      Button('Set Dark')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .alignRules({
          center: { anchor: '__container__', align: VerticalAlign.Center },
          middle: { anchor: '__container__', align: HorizontalAlign.Center }
        })
        .onClick(() => {
          let options: preferences.Options = { name: 'myStore' };
          let context = getContext(this) as common.Context;
          let dataPreferences = preferences.getPreferencesSync(context, options);
          getContext().getApplicationContext().setColorMode(ConfigurationConstant.ColorMode.COLOR_MODE_DARK);
          console.info("The key 'startup' does not contain.");
          dataPreferences.putSync('color', true);
          dataPreferences.flush((err: BusinessError) => {
            if (err) {
              console.error("Failed to flush. code ="+err.code+", message ="+err.message);
              return;
            }
            console.info("Succeeded in flushing.");
          })
        })
      Button('Set ligh')
        .onClick(() => {
          let options: preferences.Options = { name: 'myStore' };
          let context = getContext(this) as common.Context;
          let dataPreferences = preferences.getPreferencesSync(context, options);
          getContext().getApplicationContext().setColorMode(ConfigurationConstant.ColorMode.COLOR_MODE_LIGHT);
          dataPreferences.putSync('color', false);
          dataPreferences.flush((err: BusinessError) => {
            if (err) {
              console.error("Failed to flush. code ="+err.code+", message ="+err.message);
              return;
            }
            console.info("Succeeded in flushing.");
          })
        })
    }
    .height('100%')
    .width('100%')
  }
}

//EntryAbility.ets:

import { AbilityConstant, common, ConfigurationConstant, UIAbility, Want } from '[@kit](/user/kit).AbilityKit';
import { hilog } from '[@kit](/user/kit).PerformanceAnalysisKit';
import { window } from '[@kit](/user/kit).ArkUI';
import { preferences } from '[@kit](/user/kit).ArkData';
import { BusinessError } from '[@kit](/user/kit).BasicServicesKit';

let dataPreferences: preferences.Preferences | null = null;
export default class EntryAbility extends UIAbility {
  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onCreate');
  }

  onDestroy(): void {
    hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onDestroy');
  }

  onWindowStageCreate(windowStage: window.WindowStage): void {
    hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onWindowStageCreate');
    windowStage.loadContent('pages/Index', (err) => {
      let options: preferences.Options = { name: 'myStore' };
      let context = getContext(this) as common.Context;
      let dataPreferences = preferences.getPreferencesSync(context, options);
      let value: preferences.ValueType = dataPreferences.getSync('color', false);
      console.log(value+'7667676')
      if(value) {
        this.context.getApplicationContext().setColorMode(ConfigurationConstant.ColorMode.COLOR_MODE_DARK)
      } else  {
        this.context.getApplicationContext().setColorMode(ConfigurationConstant.ColorMode.COLOR_MODE_LIGHT)
      }
      if (err.code) {
        hilog.error(0x0000, 'testTag', 'Failed to load the content. Cause: %{public}s', JSON.stringify(err) ?? '');
        return;
      }
      hilog.info(0x0000, 'testTag', 'Succeeded in loading the content.');
    });
  }

  onWindowStageDestroy(): void {
    hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onWindowStageDestroy');
  }

  onForeground(): void {
    hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onForeground');
  }

  onBackground(): void {
    hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onBackground');
  }
}