Kotlin：切换片段时尚未初始化lateinit属性userDatabase

Question

I have an activity with Three Tabs and Four Fragments. On one of the tabs (Profile tab), I have a fragment (ProfileFragment) that has a button to redirect the user to another fragment (EditorFragment) to edit the user's profile.

class ProfileFragment : Fragment() {
   
 ...

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        val v = inflater.inflate(R.layout.fragment_profile, container, false)

        val btn = v.findViewById<View>(R.id.editProfileButton) as Button

        btn.setOnClickListener {
            val fragment = EditorFragment()
            val fragmentManager = activity!!.supportFragmentManager
            val transaction = fragmentManager.beginTransaction()
            transaction.replace(R.id.fragmentContainer, fragment)

           transaction.addToBackStack(null)
            transaction.commit()
        }
        return v
    }

The EditorFragment also belongs to the Profile Tab:

        class EditorFragment : Fragment() {
        
            private lateinit var userDatabase: DatabaseReference
            private var callback: AppCallback? = null
    
        fun setCallback(callback: AppCallback) {
            this.callback = callback
            userId = callback.onGetUserId()
            userDatabase = callback.getUserDatabase().child(userId)
        }


        override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            super.onViewCreated(view, savedInstanceState)

            populateInfo(view)
        }

    
       fun populateInfo(view: View) {
        userDatabase.addListenerForSingleValueEvent(object : ValueEventListener {
            override fun onDataChange(p0: DataSnapshot) {
             ...
            }

When I give priority to the EditorFragment to open first, everything goes well but when I am in ProfileFragment and try to use the button to redirect to Editor Fragment, the app crashes.

ERROR:

lateinit property userDatabase has not been initialized
at com.example.app.fragments.EditorFragment.populateInfo(EditorFragment.kt:138)

Which refers to this line on EditorFragment populateInfo():

userDatabase.addListenerForSingleValueEvent(object : ValueEventListener {

Aditional Information that may help:

• The button is functioning when I delete everything related to the issue.

Main Activity:

class MainActivity : AppCompatActivity(), MainCallback {
             
    private lateinit var userDatabase: DatabaseReference
    private var profileFragment: ProfileFragment? = null
    private var editorFragment: EditorFragment? = null

    ...

        navigationTabs.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
        ...

            override fun onTabSelected(tab: TabLayout.Tab?) {
                when(tab) {
                    profileTab -> {
                        if (profileFragment == null) {
                            profileFragment = ProfileFragment()
                            profileFragment!!.setCallback(this@MainActivity)
                        }
                        replaceFragment(profileFragment!!)

                        if (editorFragment == null) {
                            editorFragment = EditorFragment()
                            editorFragment!!.setCallback(this@MainActivity)
                        }
                        replaceFragment (editorFragment!!)
                    }
         ...


     fun replaceFragment(fragment: Fragment){
         supportFragmentManager.beginTransaction()
        .replace(R.id.fragmentContainer, fragment)
        .commit()
     }

Answer 1

When you give priority to EditorFragment to open first your onTabSelectListener in triggered hence calling your setCallBack that initializes your database, when you open the ProfileFragment first it is not triggering your onTabSelectedListener hence it doesnt call your setCallBack and it doesn't initializes your database. Let me know if it helps you to solve the problem.