Flutter webview加载时显示进度

class _BlogState extends State<Blog> {
  final Completer<WebViewController> _controller =
      Completer<WebViewController>();
  bool isLoading = true;  // 设置状态

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text(homeTitle),
        actions: <Widget>[
          BlogMenu(_controller.future),
        ],
      ),
      body: Stack(
        children: [
          WebView(
            initialUrl: homePage,
            javascriptMode: JavascriptMode.unrestricted,
            onWebViewCreated: (WebViewController webViewController) {
              _controller.complete(webViewController);
            },
            navigationDelegate: (NavigationRequest request) {
              var url = request.url;
              print("visit $url");
              setState(() {
                isLoading = true; // 开始访问页面，更新状态
              });

              return NavigationDecision.navigate;
            },
            onPageFinished: (String url) {
              setState(() {
                isLoading = false; // 页面加载完成，更新状态
              });
            },
          ),
          isLoading
              ? Container(
                  child: Center(
                    child: CircularProgressIndicator(),
                  ),
                )
              : Container(),
        ],
      ),
      floatingActionButton: getFloatingButton(),
    );
  }