如何在web组件中获取和设置UserAgent

import { webview } from '@kit.ArkWeb';
@Entry
@Component
struct Index {
  controller: webview.WebviewController = new webview.WebviewController();
  @State customUserAgent: string = '';
  @State userAgent: string = '';

  aboutToAppear(): void {
    webview.once('webInited', () => {
      try {
初始化完成时获取UserAgent。
        // Mozilla/5.0 (Phone; OpenHarmony 4.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36  ArkWeb/4.1.6.1 Mobile
        this.userAgent = this.controller.getUserAgent();  
      } catch (error) {
        console.error(`get init UserAgent Error: ${JSON.stringify(error)}`);
      }
    })
  }

  build() {
    Column() {
      Web({ src: 'www.example.com', controller: this.controller })
        .width('100%')
        .layoutWeight(1)
      Column({ space: 12 }) {
自定义用户代理：' + this.customUserAgent)
          .width('100%')
          .margin({ top: 20 })
默认用户代理：' + this.userAgent)
          .width('100%')
设置自定义用户代理')
          .onClick(() => {
            try {
              let userAgent = this.customUserAgent.length > 0 ? this.customUserAgent : this.userAgent;
              this.controller.setCustomUserAgent(userAgent + ' test');
            } catch (error) {
              console.error(`setCustomUserAgent Error: ${JSON.stringify(error)}`);
            }
          })
获取自定义用户代理')
          .onClick(() => {
            try {
              this.customUserAgent = this.controller.getCustomUserAgent();
              console.log('getCustomUserAgent Success, userAgent: ' + this.userAgent);
            } catch (error) {
              console.error(`getCustomUserAgent Error: ${JSON.stringify(error)}`);
            }
          })
默认用户代理')
          .onClick(() => {
            try {
              this.userAgent = this.controller.getUserAgent();
              console.log('getUserAgent Success, userAgent: ' + this.userAgent);
            } catch (error) {
              console.error(`getUserAgent Error: ${JSON.stringify(error)}`);
            }
          })
      }
      .width('100%')
    }
    .width('100%')
    .height('100%')
  }
}