HarmonyOS Web 组件设置自定义 UA 会使 WebviewController.accessBackward() 总是返回 false

import { webview } from '@kit.ArkWeb' 
 
@Entry 
@Component 
export struct PageWeb { 
  readonly webUrl: string | Resource = 'www.huawei.com' 
  readonly controller: WebviewController = new webview.WebviewController() 
  userAgentAlreadySet: boolean = false 
  @State customUserAgent?: string = undefined 
  build() { 
    if (this.customUserAgent){ 
      Web({ src:'', controller: this.controller }) 
        .size({ width: '100%', height: '100%' }) 
        .javaScriptAccess(true) 
        .fileAccess(true) 
        .domStorageAccess(true) 
        .databaseAccess(true) 
        .mixedMode(MixedMode.Compatible) 
        .zoomAccess(true) 
        .geolocationAccess(true) 
        .multiWindowAccess(false) 
        .overviewModeAccess(false) 
        .darkMode(WebDarkMode.Auto) 
        .pinchSmooth(true) 
        .onControllerAttached(() => { 
          this.applyCustomUserAgent() 
        })} 
  } 
 
 
  aboutToAppear(): void { 
    // 模拟异步构建 customUserAgent 过程 
    setTimeout(() => this.customUserAgent = 'ua/value', 200) 
  } 
 
 
  applyCustomUserAgent(): void { 
    if (this.userAgentAlreadySet || !this.customUserAgent) return 
    this.userAgentAlreadySet = true 
    let defaultUserAgent = this.controller.getUserAgent() 
    this.controller.setCustomUserAgent(defaultUserAgent + ' ' + this.customUserAgent) 
    this.controller.loadUrl(this.webUrl) 
  } 
 
 
  onBackPress(): boolean | void { 
    if (this.controller.accessBackward()) { 
      this.controller.backward() 
      return true 
    } 
  } 
}