🎉 Add support for Android Plugin API v2 (#67)

Still supports API v1.

Co-authored-by: junying1 <jying@simplec.com>

Author: junying1

android/src/main/kotlin/com/linusu/flutter_web_auth/FlutterWebAuthPlugin.kt

@@ -6,21 +6,39 @@ import android.net.Uri
 
 import androidx.browser.customtabs.CustomTabsIntent
 
+import io.flutter.embedding.engine.plugins.FlutterPlugin
+import io.flutter.plugin.common.BinaryMessenger
 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 FlutterWebAuthPlugin(private val context: Context): MethodCallHandler {
+class FlutterWebAuthPlugin(private var context: Context? = null, private var channel: MethodChannel? = null): MethodCallHandler, FlutterPlugin {
   companion object {
     val callbacks = mutableMapOf<String, Result>()
 
     @JvmStatic
     fun registerWith(registrar: Registrar) {
-      val channel = MethodChannel(registrar.messenger(), "flutter_web_auth")
-      channel.setMethodCallHandler(FlutterWebAuthPlugin(registrar.activity() ?: registrar.context()))
+        val plugin = FlutterWebAuthPlugin()
+        plugin.initInstance(registrar.messenger(), registrar.context())
     }
+
+  }
+
+  fun initInstance(messenger: BinaryMessenger, context: Context) {
+      this.context = context
+      channel = MethodChannel(messenger, "flutter_web_auth")
+      channel?.setMethodCallHandler(this)
+  }
+
+  override public fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) {
+      initInstance(binding.getBinaryMessenger(), binding.getApplicationContext())
+  }
+
+  override public fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
+      context = null
+      channel = null
   }
 
   override fun onMethodCall(call: MethodCall, resultCallback: Result) {