在 Android 应用中的活动之间切换后，如何切换回之前的片段？

Question

I have one custom fragment, Fragment A and two custom activities, Activity A and Activity B. I have a button on each of them in the top left hand corner which when clicked should go back to the previous fragment or activity. I switch from Fragment A to Activity A using an intent(...) call and the same thing when switching from Activity A to Activity B. I switch from Activity B to Activity A with an intent(...) call but I cannot switch from Activity A to fragment A using an intent(...) call. I have tried using finish() in Activity A to get back to Fragment A but it sometimes results in Activity B being displayed if I have previously visited it before trying to switch to Fragment A. Any help in solving this conundrum would be greatly appreciated.

Here is the code for Fragment A:

package com.riverstonetech.gositeuk.ui.scotland

import android.content.Intent
import android.content.Intent.getIntent
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 androidx.fragment.app.FragmentManager
import com.google.firebase.firestore.FirebaseFirestore
import com.riverstonetech.gositeuk.CountriesActivity
import com.riverstonetech.gositeuk.R
import com.riverstonetech.gositeuk.RegionActivity
import com.riverstonetech.gositeuk.returnToFragment
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 fragmentTransaction = returnToFragment.fragmentManager.beginTransaction()
        fragmentTransaction.add(R.id.navigation_scotland, this)
        fragmentTransaction.addToBackStack("ScotlandFragment")
        fragmentTransaction.commit()

        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
    }
}

Here is the relevant code for Activity A:

    fun previousSubCountryListButtonClicked(view: View) {

        if ( returnToFragment.fragmentManager.backStackEntryCount > 0) {

            returnToFragment.fragmentManager.popBackStack()

        }

    }

Here is the relevant code for my Activity B:

    fun listPreviousSitesClicked(view: View) {

        var intent: Intent

        when (previousActivityName) {

            "CountyActivity" -> {
                intent = Intent(this, CountyActivity::class.java)
                intent.putExtra("SUB_COUNTRY", subCountry)
                startActivity(intent)
            }
            "RegionActivity" -> {
                intent = Intent(this, RegionActivity::class.java)
                intent.putExtra("SUB_COUNTRY", subCountry)
                startActivity(intent)
            }

            else -> Log.i("INFO", "Unknown activity")

        }


    }

Here is the code for my object returnToFragment

package com.riverstonetech.gositeuk

import androidx.fragment.app.FragmentActivity

object returnToFragment: FragmentActivity() {

    var fragmentManager = supportFragmentManager

}

Answer 1

You are switching from Fragment A to Activity A using the intent function.

you are doing the same thing when moving forward from Activity A to Activity B .

When you are going back, finish Activity B then finish Activity A . Fragment A will then be visible to the user.

Don't go back by calling the intent method, just use finish.