Cannot invoke method - Method Channel in Flutter - flutter

Question

I'm trying to write platform specific code in Flutter. First of all, created a method to obtain battery temperature inside MainActivity.kt
This is my full code in MainActivity.kt file:
package com.xyz.zyx
import android.os.BatteryManager;
import androidx.annotation.NonNull
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import io.flutter.embedding.android.FlutterFragmentActivity
import io.flutter.plugin.common.BinaryMessenger
import io.flutter.plugin.common.EventChannel
import io.flutter.plugin.common.MethodCall
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugin.common.MethodChannel.MethodCallHandler
import io.flutter.plugin.common.MethodChannel.Result
import io.flutter.plugin.common.PluginRegistry.Registrar
class MainActivity: FlutterFragmentActivity() {
// ...
private var batteryManager: BatteryManager? = null
private var methodChannel: MethodChannel? = null
private var temperatureChannel: EventChannel? = null
override fun configureFlutterEngine(#NonNull flutterEngine: FlutterEngine) {
super.configureFlutterEngine(flutterEngine)
MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "battery").setMethodCallHandler {
call, result ->
if (call.method == "getBatteryTemperature") {
val batteryTemperature = getBatteryTemperature()
if (batteryTemperature != -1) {
result.success(batteryTemperature)
} else {
result.error("UNAVAILABLE", "Battery temperature not available.", null)
}
} else {
result.notImplemented()
}
}
}
private fun getBatteryTemperature(): Int {
val batteryStatus: Intent? =
IntentFilter(Intent.ACTION_BATTERY_CHANGED).let { ifilter ->
this.registerReceiver(null, ifilter)
val batteryTemperature: Int
val batteryManager =
getSystemService(Context.BATTERY_SERVICE) as BatteryManager
batteryTemperature = intent.getIntExtra(BatteryManager.EXTRA_TEMPERATURE, -99)
return batteryTemperature
}
}
}
This is how I call my platform specific code from Flutter side:
static const platform = MethodChannel('battery');
Future<void> _getBatteryTemp() async {
String batteryLevel;
try {
var result = await platform.invokeMethod('getBatteryTemperature');
batteryLevel = 'Battery temperature at $result % .';
} on PlatformException catch (e) {
batteryLevel = "Failed to get battery level: '${e.message}'.";
}
print(batteryLevel);
}
Lastly, this is the error on Flutter app running on an Android device. It throws an MissingPluginException even though there is a method called getBatteryTemperature, it says there isn't.
E/flutter (25427): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: MissingPluginException(No implementation found for method getBatteryTemperature on channel battery)
E/flutter (25427): #0 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:294:7)
Is there something did I miss to implement in my code? Why does it not work?