Why can't I use an intent to transition back to a previous fragment in my Android app?

Question

I make a transition from a fragment to an activity but I am unable to transition back to the fragment without my app crashing.

Here is my fragment code:

package com.riverstonetech.gositeuk.ui.scotland

import android.content.Intent
import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ArrayAdapter
import android.widget.ProgressBar
import androidx.fragment.app.Fragment
import com.google.firebase.firestore.FirebaseFirestore
import com.riverstonetech.gositeuk.CountriesActivity
import com.riverstonetech.gositeuk.R
import com.riverstonetech.gositeuk.RegionActivity
import kotlinx.android.synthetic.main.fragment_scotland.*

class ScotlandFragment : Fragment() {

    // Access a Cloud Firestore instance
    val db = FirebaseFirestore.getInstance()
    lateinit var adapter : ArrayAdapter<String>

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

        (requireActivity() as CountriesActivity).initializeCustomActionBar(R.drawable.scotland_flag, R.string.title_regions)

        var regions : ArrayList<String>

        val docRef = db.collection("UKSites").document("Scotland")

        val progressBar: ProgressBar = root.findViewById(R.id.regionsLoadingProgressBar)

        docRef.get()
            .addOnSuccessListener { document ->

                progressBar?.visibility = ProgressBar.VISIBLE

                if (document != null) {

                    regions = document.get("Regions") as ArrayList<String>

                    adapter = ArrayAdapter(requireContext(), R.layout.list_item, regions)

                    regionsListView.adapter = adapter

                    regionsListView.setOnItemClickListener { parent, view, position, id ->

                        val intent = Intent(activity!!, RegionActivity::class.java)
                        intent.putExtra("SUB_COUNTRY", regions[position])
                        startActivity(intent)


                    }

                    progressBar?.visibility = ProgressBar.GONE

                } else {
                    Log.d("Debug", "No such document")
                }
            }
            .addOnFailureListener { exception ->
                Log.d("Debug", "get failed with ", exception)
            }

        return root
    }
}

And here is the relevant code in my activity class RegionActivity :

    fun previousSubCountryListButtonClicked(view: View) {

        val intent: Intent = Intent(this, ScotlandFragment::class.java)
        startActivity(intent)

    }

Here is the error output in the logcat window:

2020-02-10 15:46:54.089 27008-27008/com.riverstonetech.gositeuk E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.riverstonetech.gositeuk, PID: 27008
    java.lang.IllegalStateException: Could not execute method for android:onClick
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:402)

I don't have enough knowledge of fragments and activity to work out why this doesn't work so any help would be appreciated.

Answer 1

You are making this way more complicated than it needs to be.

To return from RegionActivity to the previous Activity/Fragment , you just need to call finish() . That will destroy RegionActivity and return to whatever Activity was underneath it, in the same state it was in when you launched RegionActivity .

Answer 2

我使用了finish()而不是尝试使用意图切换到片段。