Requested flutter engine does not exist in Add to app

Question

I have flutter into the existing native app (Add to app) with a cached flutter engine.

override fun onCreate(savedInstanceState: Bundle?) {
        Log.d(TAG, "onCreate")
        
        
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)
        context = this.application.applicationContext
        if (!FlutterEngineCache.getInstance().contains(
                FLUTTER_ENGINE
            )
        ) {
            mFlutterEngine = FlutterEngine(context)
            mFlutterEngine.dartExecutor
                .executeDartEntrypoint(DartExecutor.DartEntrypoint.createDefault())
            FlutterEngineCache.getInstance()
                .put(FLUTTER_ENGINE, mFlutterEngine)
        }
        //Create Flutter Fragment
        mFragmentManager = supportFragmentManager
        mFlutterFragment = mFragmentManager.findFragmentByTag(FLUTTER_FRAGMENT) as FlutterFragment?
        if (mFlutterFragment == null) {
            mFlutterFragment =
                FlutterFragment.withCachedEngine(FLUTTER_ENGINE).transparencyMode(FlutterView.TransparencyMode.opaque).build()
            mFragmentManager
                .beginTransaction()
                .add(R.id.fragment_container, mFlutterFragment as Fragment, FLUTTER_FRAGMENT)
                .commit()
        } else {
            mFragmentManager
                .beginTransaction()
                .show(mFragmentManager.findFragmentByTag(FLUTTER_FRAGMENT)!!)
                .commit()
        }
}

I am getting the following crash in the production app

  Caused by: java.lang.IllegalStateException: The requested cached FlutterEngine did not exist in the FlutterEngineCache: 'FLUTTER_ENGINE'
        at io.flutter.embedding.android.FlutterActivityAndFragmentDelegate.setupFlutterEngine(FlutterActivityAndFragmentDelegate.java:211)
        at io.flutter.embedding.android.FlutterActivityAndFragmentDelegate.onAttach(FlutterActivityAndFragmentDelegate.java:157)
        at io.flutter.embedding.android.FlutterFragment.onAttach(FlutterFragment.java:597)
        at androidx.fragment.app.Fragment.performAttach(Fragment.java:2574)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:828)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
        at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2659)
        at androidx.fragment.app.FragmentManagerImpl.dispatchCreate(FragmentManagerImpl.java:2607)
        at androidx.fragment.app.FragmentController.dispatchCreate(FragmentController.java:235)
        at androidx.fragment.app.FragmentActivity.onCreate(FragmentActivity.java:316)
        at androidx.appcompat.app.AppCompatActivity.onCreate(AppCompatActivity.java:106)
        at com.flutter.android.MainActivity.onCreate(MainActivity.kt:33)
 

Solution

How to reproduce

1. Open developer settings, set "Background processes" to "No Background Processes" and set on the Don't keep activities.

2. Open the app press and home

3. Open the app again .. it will crash with the exception.

   Caused by: java.lang.IllegalStateException: The requested cached FlutterEngine did not exist in the FlutterEngineCache: 'FLUTTER_ENGINE'

Solution

initialize the flutter engine before super.oncreate()

override fun onCreate(savedInstanceState: Bundle?) {
        Log.d(TAG, "onCreate")
         context = this.application.applicationContext
        if (!FlutterEngineCache.getInstance().contains(
                FLUTTER_ENGINE
            )
        ) {
            mFlutterEngine = FlutterEngine(context)
            mFlutterEngine.dartExecutor
                .executeDartEntrypoint(DartExecutor.DartEntrypoint.createDefault())
            FlutterEngineCache.getInstance()
                .put(FLUTTER_ENGINE, mFlutterEngine)
        }
       
        
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)
        //Create Flutter Fragment
        mFragmentManager = supportFragmentManager
        mFlutterFragment = mFragmentManager.findFragmentByTag(FLUTTER_FRAGMENT) as FlutterFragment?
        if (mFlutterFragment == null) {
            mFlutterFragment =
                FlutterFragment.withCachedEngine(FLUTTER_ENGINE).transparencyMode(FlutterView.TransparencyMode.opaque).build()
            mFragmentManager
                .beginTransaction()
                .add(R.id.fragment_container, mFlutterFragment as Fragment, FLUTTER_FRAGMENT)
                .commit()
        } else {
            mFragmentManager
                .beginTransaction()
                .show(mFragmentManager.findFragmentByTag(FLUTTER_FRAGMENT)!!)
                .commit()
        }

Comments

[Renso Lohuis]

I have an app with 3 tabs, one of them holds a flutter fragment. The crash also happened to our app on production, but I could not reproduce it. Also not with the reproduction scenario as described above. I ended up removing the flutter engine manually at onDestroy to reproduce the situation. And as a solution I check if the flutter tab is open and then create the engine as stated above.