How to host an Android Fragment in a Flutter app as a native view when the context is a MutableContextWrapper and needs to be added to the View class Ask Question

Question

I need to host an embedded native view into my Flutter app,
I have an Android Fragment and me trying to add it to the View class that registered in FlutterEngine
but Fragments need to be added:

(context as FragmentActivity).supportFragmentManager

And that does not work due to the existing context is MutableContextWrapper

Any help, please?

MainActivity:

class MainActivity: FlutterActivity() {
    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        flutterEngine
            .platformViewsController
            .registry
            .registerViewFactory("EmbeddedNavigationView.kt", EmbeddedNavigationFactory(mapOf("text" to "hello!")))
    }


}

EmbeddedNavigationView:

class EmbeddedNavigationView(context: Context, val viewParams: Map<String, Any>) : View(context), PlatformView {

    private lateinit var fragmentMap: Fragment
    private val fragment: Fragment = FlutterFragment.createDefault()
    init {
        initObjects()
        initSubView()
    }
    private fun initObjects() {
        fragmentMap = MapFragment()
    }
    private fun initSubView() {
        addFragment(fragmentMap)
    }
    private fun addFragment(fragment: Fragment) {

        // thow error due to MutableContextWrapper is not a FragmentActivity

        val fragmentManager = (context as FragmentActivity).supportFragmentManager

        val transaction = fragmentManager.beginTransaction()
        transaction.add(R.id.fragment_map, fragment)
        transaction.commit()
    }

    private fun removeFragment(fragment: Fragment) {
        val fragmentManager = (context as FragmentActivity).supportFragmentManager

        val transaction = fragmentManager.beginTransaction()
        transaction.remove(fragment)
        transaction.commit()
    }


    override fun onDraw(canvas: Canvas) {
        // Draw the view's content
        super.onDraw(canvas)
    }

    override fun onDetachedFromWindow() {
        // Remove the fragment when the view is detached
        fragmentMap?.let {
            (context as AppCompatActivity).supportFragmentManager.beginTransaction().remove(it).commit()
        }
        super.onDetachedFromWindow()
    }

    class MyFragment : Fragment() {
        // Fragment code here
    }

    override fun getView(): View? {
        return this

        TODO("Not yet implemented")

    }

    override fun dispose() {
        // impl dispose



        TODO("Not yet implemented")
    }


}

EmbeddedNavigationFactory:

class EmbeddedNavigationFactory(private val createParams: Map<String, Any>?) : PlatformViewFactory(StandardMessageCodec.INSTANCE) {

    override fun create(context: Context, viewId: Int, args: Any?): PlatformView {
        val viewParams = createParams ?: args as? Map<String, Any> ?: mapOf()

        return EmbeddedNavigationView(context, viewParams)
    }

}

MapFragment:

class MapFragment : androidx.fragment.app.Fragment() { ... }

Logs:

Launching lib/main.dart on 2201117TG in debug mode...
Running Gradle task 'assembleDebug'...
✓  Built build/app/outputs/flutter-apk/app-debug.apk.
Installing build/app/outputs/flutter-apk/app-debug.apk...
Debug service listening on ws://127.0.0.1:50805/JtPxjixFiC4=/ws
Syncing files to device 2201117TG...
E/MethodChannel#flutter/platform_views(15059): Failed to handle method call
E/MethodChannel#flutter/platform_views(15059): java.lang.ClassCastException: android.content.MutableContextWrapper cannot be cast to androidx.fragment.app.FragmentActivity
E/MethodChannel#flutter/platform_views(15059):  at com.example.mapbox_android_update.EmbeddedNavigationView.addFragment(EmbeddedNavigationView.kt:29)
E/MethodChannel#flutter/platform_views(15059):  at com.example.mapbox_android_update.EmbeddedNavigationView.initSubView(EmbeddedNavigationView.kt:26)
E/MethodChannel#flutter/platform_views(15059):  at com.example.mapbox_android_update.EmbeddedNavigationView.<init>(EmbeddedNavigationView.kt:20)
E/MethodChannel#flutter/platform_views(15059):  at com.example.mapbox_android_update.EmbeddedNavigationFactory.create(EmbeddedNavigationFactory.kt:19)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.plugin.platform.PlatformViewsController$1.createPlatformView(PlatformViewsController.java:503)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.plugin.platform.PlatformViewsController$1.createForTextureLayer(PlatformViewsController.java:191)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.embedding.engine.systemchannels.PlatformViewsChannel$1.create(PlatformViewsChannel.java:128)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.embedding.engine.systemchannels.PlatformViewsChannel$1.onMethodCall(PlatformViewsChannel.java:55)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:258)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.embedding.engine.dart.DartMessenger.invokeHandler(DartMessenger.java:295)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.embedding.engine.dart.DartMessenger.lambda$dispatchMessageToQueue$0$io-flutter-embedding-engine-dart-DartMessenger(DartMessenger.java:322)
E/MethodChannel#flutter/platform_views(15059):  at io.flutter.embedding.engine.dart.DartMessenger$$ExternalSyntheticLambda0.run(Unknown Source:12)
E/MethodChannel#flutter/platform_views(15059):  at android.os.Handler.handleCallback(Handler.java:938)
E/MethodChannel#flutter/platform_views(15059):  at android.os.Handler.dispatchMessage(Handler.java:99)
E/MethodChannel#flutter/platform_views(15059):  at android.os.Looper.loopOnce(Looper.java:210)
E/MethodChannel#flutter/platform_views(15059):  at android.os.Looper.loop(Looper.java:299)
E/MethodChannel#flutter/platform_views(15059):  at android.app.ActivityThread.main(ActivityThread.java:8309)
E/MethodChannel#flutter/platform_views(15059):  at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#flutter/platform_views(15059):  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:556)
E/MethodChannel#flutter/platform_views(15059):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1038)
E/flutter (15059): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: PlatformException(error, android.content.MutableContextWrapper cannot be cast to androidx.fragment.app.FragmentActivity, null, java.lang.ClassCastException: android.content.MutableContextWrapper cannot be cast to androidx.fragment.app.FragmentActivity
E/flutter (15059):  at com.example.mapbox_android_update.EmbeddedNavigationView.addFragment(EmbeddedNavigationView.kt:29)
E/flutter (15059):  at com.example.mapbox_android_update.EmbeddedNavigationView.initSubView(EmbeddedNavigationView.kt:26)
E/flutter (15059):  at com.example.mapbox_android_update.EmbeddedNavigationView.<init>(EmbeddedNavigationView.kt:20)
E/flutter (15059):  at com.example.mapbox_android_update.EmbeddedNavigationFactory.create(EmbeddedNavigationFactory.kt:19)
E/flutter (15059):  at io.flutter.plugin.platform.PlatformViewsController$1.createPlatformView(PlatformViewsController.java:503)
E/flutter (15059):  at io.flutter.plugin.platform.PlatformViewsController$1.createForTextureLayer(PlatformViewsController.java:191)
E/flutter (15059):  at io.flutter.embedding.engine.systemchannels.PlatformViewsChannel$1.create(PlatformViewsChannel.java:128)
E/flutter (15059):  at io.flutter.embedding.engine.systemchannels.PlatformViewsChannel$1.onMethodCall(PlatformViewsChannel.java:55)
E/flutter (15059):  at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:258)
E/flutter (15059):  at io.flutter.embedding.engine.dart.DartMessenger.invokeHandler(DartMessenger.java:295)
E/flutter (15059):  at io.flutter.embedding.engine.dart.DartMessenger.lambda$dispatchMessageToQueue$0$io-flutter-embedding-engine-dart-DartMessenger(DartMessenger.java:322)
E/flutter (15059):  at io.flutter.embedding.engine.dart.DartMessenger$$ExternalSyntheticLambda0.run(Unknown Source:12)
E/flutter (15059):  at android.os.Handler.handleCallback(Handler.java:938)
E/flutter (15059):  at android.os.Handler.dispatchMessage(Handler.java:99)
E/flutter (15059):  at android.os.Looper.loopOnce(Looper.java:210)
E/flutter (15059):  at android.os.Looper.loop(Looper.java:299)
E/flutter (15059):  at android.app.ActivityThread.main(ActivityThread.java:8309)
E/flutter (15059):  at java.lang.reflect.Method.invoke(Native Method)
E/flutter (15059):  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:556)
E/flutter (15059):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1038)
E/flutter (15059): )
E/flutter (15059): #0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:653:7)
E/flutter (15059): #1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:315:18)
E/flutter (15059): <asynchronous suspension>
E/flutter (15059): #2      TextureAndroidViewController._sendCreateMessage (package:flutter/src/services/platform_views.dart:1141:28)
E/flutter (15059): <asynchronous suspension>
E/flutter (15059): #3      AndroidViewController.create (package:flutter/src/services/platform_views.dart:801:5)
E/flutter (15059): <asynchronous suspension>
E/flutter (15059): #4      AndroidViewController.setSize (package:flutter/src/services/platform_views.dart:828:7)
E/flutter (15059): <asynchronous suspension>
E/flutter (15059): #5      RenderAndroidView._sizePlatformView (package:flutter/src/rendering/platform_view.dart:182:29)
E/flutter (15059): <asynchronous suspension>
E/flutter (15059): 
E/_android_updat(15059): open libmigui.so failed! dlopen - dlopen failed: library "libmigui.so" not found
D/DecorView[](15059): onWindowFocusChanged hasWindowFocus true

adding this android native fragment to flutter app

score 0 · Answer 1 · Apr 6, 2023

It seems that the issue is caused by trying to cast MutableContextWrapper to FragmentActivity, which is not possible.

To solve this issue, you can try to get the actual activity instance from the MutableContextWrapper using the getBaseContext() method, which returns the original context that the MutableContextWrapper is wrapping.

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