HarmonyOS 鸿蒙Next api 12上，this.controller.accessBackward() 返回值一直返回false

setCustomUserAgent设置后与web页面的跳转时序是web跳转后才设置UserAgent，这就导致页面跳转了但新agent关联的页面堆栈数仍只有一个,webviewController.accessBackward()总是返回false。 参考链接：https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-webview-V5#setcustomuseragent10

建议在setCustomUserAgent方法后，调用loadUrl，且使用onControllerAttached替换onLoadIntercept进行applyCustomUserAgent方法的调用，参考demo如下：

import { webview } from '@kit.ArkWeb'

@Entry
@Component
export struct PageWeb {
  readonly webUrl: string | Resource = 'www.baidu.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
    }
  }
}