Android app generating Exception: androidx.fragment.app.Fragment$Instantiationexception

Question

My app is in production and I’m having a problem in a small part of the devices, I haven’t been able to identify the reason or at least reproduce the problem in a test environment, I did some research looking for more information, but without success, I would like the community to direct me to possible situations that may be generating this problem. My app is simple, it’s a news app and when it has new news the app notifies users.

The devices that presented the error:

1. Samsung Galaxy A20 (A20), 2816MB RAM, Android 9
2. Samsung Galaxy J4 (j4lte), 2048MB RAM, Android 9
3. Motorola Moto G (5th Gen) (Cedric), 2048MB RAM, Android 8.1
4. Samsung Galaxy J4 Core (j4corelte), 1024MB RAM, Android 8.1

As I don’t know which parts of the code are related to the problem, I didn’t put any specific class, but if anyone wants to just ask in the comments, for example I believe it is related to notification.

The error was captured straight from google play console.

java.lang.Runtimeexception:

at android.app.Activitythread.performLaunchActivity (Activitythread.java:3121) at android.app.Activitythread.handleLaunchActivity (Activitythread.java:3264) at android.app.servertransaction.LaunchActivityItem.execute (Launchactivityitem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks (Transactionexecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute (Transactionexecutor.java:68) at android.app.Activitythread$H.handleMessage (Activitythread.java:1955) at android.os.Handler.dispatchMessage (Handler.java:106) at android.os.Looper.loop (Looper.java:214) at android.app.Activitythread.main (Activitythread.java:7078) at java.lang.reflect.Method.invoke (Native Method) at com.android.Internal.os.Runtimeinit$Methodandargscaller.run (Runtimeinit.java:494) at com.android.Internal.os.Zygoteinit.main (Zygoteinit.java:965)

Caused by: androidx.fragment.app.Fragment$Instantiationexception:

at androidx.fragment.app.Fragment.instantiate (Fragment.java:538)
at androidx.fragment.app.FragmentContainer.instantiate (Fragmentcontainer.java:57) at androidx.fragment.app.FragmentManagerImpl$6.instantiate (Fragmentmanagerimpl.java:2851) at androidx.fragment.app.FragmentState.instantiate (Fragmentstate.java:85) at androidx.fragment.app.FragmentManagerImpl.restoreSaveState (Fragmentmanagerimpl.java:2488) at androidx.fragment.app.FragmentController.restoreSaveState (Fragmentcontroller.java:195) at androidx.fragment.app.FragmentActivity.onCreate (Fragmentactivity.java:288) at androidx.appcompat.app.AppCompatActivity.onCreate (Appcompatactivity.java:106) at xxx.xxxx.xxxxx.MainActivity.onCreate (Mainactivity.kt:70) at android.app.Activity.performCreate (Activity.java:7339) at android.app.Activity.performCreate (Activity.java:7330) at android.app.Instrumentation.callActivityOnCreate (Instrumentation.java:1275) at android.app.Activitythread.performLaunchActivity (Activitythread.java:3101)

Caused by: java.lang.Nosuchmethodexception:

at java.lang.Class.getConstructor0 (Class.java:2328) at java.lang.Class.getConstructor (Class.java:1725) at androidx.fragment.app.Fragment.instantiate (Fragment.java:523)

Part of the class the problem points to

Mainactivity.kt

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState) // Linha 70
        setContentView(R.layout.activity_main)

        ...
}

Other classes that may be related to the problem

Pageradapter.kt

class PagerAdapter(val fragmentActivity: FragmentActivity, private var lista: MutableList<Blog>) : FragmentStateAdapter(fragmentActivity) {


    override fun getItemCount(): Int {
        return lista.size+1
    }

    override fun createFragment(position: Int): Fragment {

        return if(position<lista.size)
            Tab(lista[position])
        else
            OutraTab() // tab fixa no final

    }

}

Tab.kt

 class Tab(private val blog: Blog) : Fragment() {

        ...

        override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
            val view = inflater.inflate(R.layout.tab, container, false)

        ...


        }

}

Outratab.kt

   class OutraTab : Fragment() {

        override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
            val view = inflater.inflate(R.layout.tab_outra, container, false)

        ...


        }

    }

Obs. Outratab.kt is similar to Tab.kt, only without the parameter blog it contains fixed content.

Answer 1

Summary

Your fragments need a default constructor (no arguments) so that Android can recreate them when necessary (when changing the orientation of the phone, for example).

Explanation

When there is a change of configuration on Android (such as change in portrait orientation to landscape, or change of language), your Activity is recreated.

In the recreation process, the Fragments that will be recreated will have a call Construtor(), i.e., the constructor without arguments. The fact that you do not have this constructor generates the following error (which you specified):

Caused by: java.lang.NoSuchMethodException:
at java.lang.Class.getConstructor0 (Class.java:2328) at java.lang.Class.getConstructor

According to the documentation of configuration changes android:

Some device settings may change during runtime, such as screen orientation, keyboard availability, and multi-window mode activation. When a change occurs, Android needs to restart running Activity (onDestroy() is called, followed by onCreate()).

Restart behavior is designed to help the application adapt to new settings by automatically updating the application with alternative features that match the device configuration.

Solution with New Instance Pattern (Newinstance)

This pattern allows you to pass arguments to a fragment without creating a constructor other than the default one. The pattern exists in both Java how much in Kotlin, but below I explain the process in Kotlin. In the fragments documentation this standard is used.

1. Create a method novaInstancia to instantiate your Fragment;
2. Get the required arguments in this method and pass to onCreate through arguments;
3. In the method onCreate, store values as attributes of your class Fragment.

Fragment code:

private const val ARG_MEU_ATRIBUTO = "meuAtributoId"

class MeuFragmento: Fragment() {
    private var meuAtributo: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            meuAtributo = it.getString(ARG_MEU_ATRIBUTO)
        }
    }

    companion object {
        fun novaInstancia(valorDoAtributo: String?) =
                MeuFragmento().apply {
                    arguments = Bundle().apply {
                        putString(ARG_MEU_ATRIBUTO, valorDoAtributo)
                    }
                }
    }
}

To instill your fragment:

val meuFragmento = MeuFragmento.novaInstancia("texto")

Newinstance with Android Studio

When you are creating a new fragment, leave the option "Include Fragment Factory methods?" and the code will be generated with the pattern described above.

Generated code:

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [BlankFragment.newInstance] factory method to
 * create an instance of this fragment.
 */
class BlankFragment : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_blank, container, false)
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment BlankFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
                BlankFragment().apply {
                    arguments = Bundle().apply {
                        putString(ARG_PARAM1, param1)
                        putString(ARG_PARAM2, param2)
                    }
                }
    }
}