Java 如何从Flatter正确调用android本机代码（包括android/IOS）？

我是颤栗的初学者。老实说，我不知道安卓工作室。 我的目标是实现本地（系统）身份验证。所以得到了只给你一个指纹选项的

local\u auth

插件。如果用户没有指纹硬件怎么办？因此，我计划通过从Flatter调用本机代码（Android）来实现这一点。 但问题是我不能正确地验证用户。 例如，在进行身份验证时，响应来自本机代码。 在进行身份验证之前，我无法暂停函数的执行。尝试同步方法 但还是没有运气

我的省道代码：

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() => runApp(Container(
  child:   Row(
    children: <Widget>[
          Column(
        children: <Widget>[
              Padding(
            padding: const EdgeInsets.all(8.0),
            child:   Center(child: MyApp()),
          ),
        ],
      ),
    ],
  ),
));

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(

        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
//    setState(() {
//      // This call to setState tells the Flutter framework that something has
//      // changed in this State, which causes it to rerun the build method below
//      // so that the display can reflect the updated values. If we changed
//      // _counter without calling setState(), then the build method would not be
//      // called again, and so nothing would appear to happen.
//      _counter++;
//    });
//    my_count();
//  var cc = code().toString();
//  print(cc);
//    if(cc == "200") {
//      Navigator.push(
//        context,
//        MaterialPageRoute(builder: (context) => SecondRoute()),
//      );
//    }else if( cc == "333") {
//      Navigator.push(context,
//      MaterialPageRoute(
//        builder: (context) => ThirdRoute()
//      ));
//    }
  code();

  }

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    my_count();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
  static const paltform = const MethodChannel('lock');

  // ignore: missing_return
  void code() async {
    int ii;
    try {
      ii = await paltform.invokeMethod('value');
    } catch (e){
      print(e);
    }
//    print(ii);
//    return ii;
    if(ii == 200) {
      Navigator.push(
        context,
        MaterialPageRoute(builder: (context) => SecondRoute()),
      );
    }else if( ii == 333) {
      Navigator.push(context,
          MaterialPageRoute(
              builder: (context) => ThirdRoute()
          ));
    }
  }

  // ignore: non_constant_identifier_names
  void my_count() async {
    try{
      _counter = await paltform.invokeMethod('getCounter');
    }catch(e){
      print(e);
    }
  }
   //if i call code() here it not executing
  code();
}



class SecondRoute extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Second Route"),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            // Navigate back to first route when tapped.
            Navigator.pop(context);
          },
          child: Text('Go back!'),
        ),
      ),
    );
  }
}

class ThirdRoute extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Third Route"),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            // Navigate back to first route when tapped.
            Navigator.pop(context);
          },
          child: Text('Go back!'),
        ),
      ),
    );
  }
}

在运行它们之后，我只有在按下按钮后才能得到成功的响应。 但我希望它应该根据本机代码的响应相应地进行路由

package com.example.native_3;

import androidx.annotation.NonNull;
import androidx.annotation.RequiresApi;

import io.flutter.embedding.android.FlutterActivity;
import io.flutter.embedding.engine.FlutterEngine;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugins.GeneratedPluginRegistrant;

import android.app.KeyguardManager;
import android.content.Intent;
import android.os.Build;

public class MainActivity extends FlutterActivity {

  private static final int LOCK_REQUEST_CODE = 221;
  private static final int SECURITY_SETTING_REQUEST_CODE = 233;
  int code = 0;
  private static final String CHANNEL = "lock";

  @Override
  public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
    GeneratedPluginRegistrant.registerWith(flutterEngine);
    new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(), CHANNEL)
            .setMethodCallHandler(
                    (call, result) -> {
                      // Note: this method is invoked on the main thread.
                      if (call.method.equals("getCounter")) {
                        synchronized (this) {
                          authenticateApp();
                        }
                        int batteryLevel = 0;


                        if (batteryLevel >= 0) {
                          result.success(batteryLevel);
                        } else {
                          result.error("UNAVAILABLE", "Battery level not available.", null);
                        }
                      } else if (call.method.equals("value")) {
                        result.success(get());
                      }
                      else {
                        result.notImplemented();
                      }
                    }
            );
  }

  private int get() {
    return code;
  }

  private synchronized void authenticateApp() {
    //Get the instance of KeyGuardManager
    KeyguardManager keyguardManager = (KeyguardManager) getSystemService(KEYGUARD_SERVICE);

    //Check if the device version is greater than or equal to Lollipop(21)
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      //Create an intent to open device screen lock screen to authenticate
      //Pass the Screen Lock screen Title and Description
      Intent i = keyguardManager.createConfirmDeviceCredentialIntent("unlock", "to unlock");
      try {
        //Start activity for result
        startActivityForResult(i, LOCK_REQUEST_CODE);

      } catch (Exception e) {

//        //If some exception occurs means Screen lock is not set up please set screen lock
//        //Open Security screen directly to enable patter lock
//        Intent intent = new Intent(Settings.ACTION_SECURITY_SETTINGS);
//        try {
//
//          //Start activity for result
//          startActivityForResult(intent, SECURITY_SETTING_REQUEST_CODE);
//        } catch (Exception ex) {
//
//          //If app is unable to find any Security settings then user has to set screen lock manually
//          textView.setText(getResources().getString(R.string.setting_label));
//        }
      }
    }
  }

  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
//    super.onActivityResult(requestCode, resultCode, data);
    synchronized (this) {
      switch (requestCode) {
        case LOCK_REQUEST_CODE:
          if (resultCode == RESULT_OK) {
            //If screen lock authentication is success update text
            code = 200;
          } else {
            //If screen lock authentication is failed update text
            code = 333;
          }
          break;
        case SECURITY_SETTING_REQUEST_CODE:
          //When user is enabled Security settings then we don't get any kind of RESULT_OK
          //So we need to check whether device has enabled screen lock or not
          if (isDeviceSecure()) {
            //If screen lock enabled show toast and start intent to authenticate user
            code = 444;
          } else {
            //If screen lock is not enabled just update text

            code = 555;
          }

          break;
      }
    }
  }
  private boolean isDeviceSecure() {
    KeyguardManager keyguardManager = (KeyguardManager) getSystemService(KEYGUARD_SERVICE);

    //this method only work whose api level is greater than or equal to Jelly_Bean (16)
    return Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN && keyguardManager.isKeyguardSecure();

    //You can also use keyguardManager.isDeviceSecure(); but it requires API Level 23

  }

  }