这个错误出现的原因是Plugin的方法没有找到，也可能是Plugin本身就没有注册成功。

在混编情况下出现这个问题，很大概率是我们在网上查找的资料中是这样写的。

import android.os.Bundle
import io.flutter.app.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugins.GeneratedPluginRegistrant
class MainActivity: FlutterActivity() {
    private val flutterMethodChannelName = "flutterCallbackMethodChannel"
    var methodChannel_callFlutter: MethodChannel? = null
    @SuppressLint("NewApi")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        GeneratedPluginRegistrant.registerWith(FlutterEngine(this@MainActivity))
        methodChannel_callFlutter = MethodChannel(flutterView, flutterMethodChannelName)
    }
}

这个代码在flutter更新了FlutterActivity后就会导致这个问题，不能再引用io.flutter.app.FlutterActivity这个FlutterActivity，而应该改用io.flutter.embedding.android.FlutterActivity。同时，继承自新版本FlutterActivity的MainActivity找不到flutterView这个方法，因此要改用getFlutterEngine().getDartExecutor().getBinaryMessenger()来代替。

代码改为：

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


class MainActivity: FlutterActivity() {
    private val flutterMethodChannelName = "flutterCallbackMethodChannel"
    var methodChannel_callFlutter: MethodChannel? = null

    @SuppressLint("NewApi")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        methodChannel_callFlutter = MethodChannel(flutterEngine!!.dartExecutor.binaryMessenger, flutterMethodChannelName)
    }

    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine);
    }
}

参考文章
https://blog.csdn.net/qq_40928212/article/details/105545875
https://blog.csdn.net/oZhuiMeng123/article/details/98120505
https://blog.csdn.net/weixin_44160584/article/details/108244793