Back From fragment B to Fragment A not working Kotlin-CodePudding

I have two fragments in my Kotlin code. When I'm pressing some of the buttons then the First fragment will inflate the second fragment. The second fragment is displayed and all works fine but when I'm pressing the back button then the Phone is going to the Home page (The application is minimized), when I click on the Recently viewed apps that open all the Opened applications on the screen and choosing my Application (that is opened) then the application got back to Fragment Alike its suppose to be.

But I don't understand why the application is minimized when I'm clicking on the back button? I just want it to go back to fragment A and do not minimize the application.

This is the code to inflate the second fragment:

                    val fragment2 = details_frag()
                    val fragmentManager: FragmentManager? = fragmentManager
                    val fragmentTransaction: FragmentTransaction =
                        fragmentManager!!.beginTransaction()


                    if (resources.configuration.orientation == Configuration.ORIENTATION_LANDSCAPE) {

                        fragmentTransaction.apply {
                            replace(R.id.fragSec, fragment2)
                            commit()
                        }
                    } else {
                        fragmentTransaction.apply {

                            replace(R.id.flFragment, fragment2)
                            commit()
                        }
                    }

The Code in the Main Activity that inflate the first fragment is:

if (resources.configuration.orientation == Configuration.ORIENTATION_LANDSCAPE) {

            supportFragmentManager.beginTransaction().apply {
                replace(R.id.fragLand, firstFrag)
                commit()
            }

            supportFragmentManager.beginTransaction()
                .add(
                    R.id.fragSec,
                    details_frag::class.java,
                    null

                ) //    .addToBackStack(null)
                .commit()


        } else {

            supportFragmentManager.beginTransaction().apply {
                replace(R.id.flFragment, firstFrag)
                commit()
            }
        }

I don't see something unusual here, it all works just great but it's just minimize my app when I'm going from the second fragment to the first fragment... (The first is inserted inside the Main Activity like you can see and I just swap the first fragment with the second one when someone clicks on something in my code...)

Thank you!!!

CodePudding user response：

You need to call addToBackstack in the FragmentTransaction (like you're doing in the second example). That makes the current transaction you're performing (replacing fragment A with B) a new state on the stack. Then when the user hits back, that state can be popped off and the transaction reversed, so you're back with fragment A in place.

If you don't add the transaction to the backstack, it becomes part of the most recent state, which is when you added A - that state becomes "added A and then replaced it with B", and when you pop that off, it goes back to "before you added A"