问函数返回null，然后打印数据

EN

import 'dart:async';
import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';

const kAndroidUserAgent =
    'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Mobile Safari/537.36';


class mainController{
  Future getdata() async{
    String data;

    final flutterWebViewPlugin = FlutterWebviewPlugin();

    flutterWebViewPlugin.launch('https://www.instagram.com/picsart/?__a=1', hidden: true, userAgent: kAndroidUserAgent,);


    flutterWebViewPlugin.onStateChanged.listen((viewState) async {
      if (viewState.type == WebViewState.finishLoad) {
        data = await flutterWebViewPlugin.evalJavascript("document.documentElement.outerText");

        print(data); //after returning null it gets printed
        
        flutterWebViewPlugin.close();
      }
    });

    return data;
  }
}