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How can I handle back button pressed with a dialog fragment?

I'm a total newbie, and my app has a main activity and a test-taking activity. Normally pressing back button in the test activity takes you back to main activity. This is fine, but I want to add a confirmation dialog asking if they really want to abandon the test first. So far I have the following in the test activity:
override fun onBackPressed() {
var exit = ExitTestDialogFragment()
exit.show(supportFragmentManager,"exit")
}
class ExitTestDialogFragment : DialogFragment() {
override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
return activity?.let {
val builder = AlertDialog.Builder(it)
builder.setTitle("Leave Test?")
builder.setMessage("Your score will be lost.")
.setPositiveButton("OK",
DialogInterface.OnClickListener { dialog, id ->
// This is where I'd like to return to Main Activity
})
.setNegativeButton("Cancel",
DialogInterface.OnClickListener { dialog, id ->
dialog.dismiss()// User cancelled the dialog
})
// Create the AlertDialog object and return it
builder.setCancelable(false)
builder.create()
} ?: throw IllegalStateException("Activity cannot be null")
}
}
I can't seem to figure out how how do what would normally be the Activity's super.onBackPressed() from the dialog fragment. Like I said, I'm super new to android, so may need a bit of an ELI5 answer.

call finish() or this.finish() inside your DialogInterface.OnClickListener. Method finish() will destroy current activity that call it, in this case its test-taking activity

You should call mainActivity from your dialog positive Button.
.setPositiveButton("OK",
DialogInterface.OnClickListener { dialog, id ->
// here you can get your current activity
//then dismiss your dialog and finish current activity
//call context.finish or activity.finish here. It will
//finish this activity
//and will take you to the previous activity (in your case
//to mainActivity)
})
If you need any further help feel free to mention it in the comments

Add this in the container dialog
dialog?.setOnKeyListener { dialog, keyCode, event ->
if (keyCode == KeyEvent.KEYCODE_BACK && event.action == KeyEvent.ACTION_UP) {
handleBack() // your code
return#setOnKeyListener true
} else
return#setOnKeyListener false
}

how can i press back just to close the app?

I implemented this function in the mainActivity of my app to ask to press back twice to exit the application, everything works but it asks me to double back press even when I want to close a fragment, how can I limit it only to the main screen?
override fun onBackPressed() {
if (backPressedTime + 2000 > System.currentTimeMillis()) {
super.onBackPressed()
}else{
Toast.makeText(this, "Premere ancora per tornare indietro", Toast.LENGTH_SHORT).show()
}
backPressedTime = System.currentTimeMillis()
}

You have to use the OnBackPressedCallBack Interface which will provide a function named handleOnBackPressed() that is called when you click navigate back button.
If your app is a Single Activity App, then you have to call finish() function that will finish your activity and this will lead to exit from the app.
You can reach finish() by using requireActivity() in the specific fragment.
If you are using Navigation Component, try to put this function in your First Destination Fragment:
private fun setOnBackButtonClickListener() {
val onBackPressedCallback = object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
if (backPressedTime + 2000 > System.currentTimeMillis()) {
requireActivity.finish()
} else {
Toast.makeText(this, "Premere ancora per tornare indietro",
Toast.LENGTH_SHORT).show()
}
}
}
requireActivity().onBackPressedDispatcher.addCallback(this, onBackPressedCallback)
}
and if you are not using Navigation Component, try to use the same function in the fragment you want to end the app from.

custom back button - Android Navigation

I have a form and want to get a confirmation message from the user before the user leaves it.
i want provide custom back button when user touch this button:
i try this:
val onBackPressedCallback = object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
}
}
requireActivity().onBackPressedDispatcher.addCallback(this,onBackPressedCallback)
but only seems to work for providing custom back behavior to the built-in software/hardware back button and not the back arrow button
How can I do this?

Use onSupportNavigateUp, and replace yourCurrentFragmentID to your current fragment id. All these should be done in MainActivity.
navController = findNavController(R.id.nav_host_fragment)
setupActionBarWithNavController(navController!!)
override fun onSupportNavigateUp(): Boolean {
return when(navController?.currentDestination?.id) {
R.id.yourCurrentFragmentID -> {
showDialog()
true
}
else -> navController?.navigateUp()!!
}
}
Edit
If your fragment already use onOptionsItemSelected, you can handle the logic by checking itemId.
override fun onOptionsItemSelected(item: MenuItem): Boolean {
val id = item.itemId
if (id == R.id.save) {
// your save button code logic
}else if(id ==android.R.id.home){
// display confirmation message
}
return super.onOptionsItemSelected(item)
}

Use this code to set Activity on backpress.
override fun onBackPressed() {
if (isDiscardChanges) {
discardDialog()
} else {
super.onBackPressed()
}
}

If you only want to go back from Activity, then you can add within AndroidManifest.xml child class Activity.
android:parentActivityName="Parent_Activity_Name

OnBackPressedCallback is being called, but app is not going back

I recently updated my dependencies to include the OnBackPressedCallback change from an interface into an abstract class.
I have set things up according to the new documentation here but I feel like things are not working as they should.
My fragment's OnCreate looks a lot like the documentation:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
requireActivity().onBackPressedDispatcher.addCallback(this) {
backPressed()
}
}
When I press the back button, the code in backPressed() is run, but nothing more happens.
I have tried calling handleBackPressed() and requireActivity().onBackPressedDispatcher.onBackPressed() and requireActivity().onBackPressed() from inside the callback, but those all cause a StackOverflowError because it seems to run that callback recursively.
There has got to be something really obvious I am missing...

There has got to be something really obvious I am missing...
You forget to disable your custom callback in you fragment before asking Activity to handle back pressed.
My solutiuon suitable for me:
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final OnBackPressedCallback callback = new OnBackPressedCallback(true) {
#Override
public void handleOnBackPressed() {
if (/*situation to handle back pressing*/){
//here handle your backPress in your fragment
} else {
setEnabled(false); //this is important line
requireActivity().onBackPressed();
}
}
};
requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);
}

When you register an OnBackPressedCallback, you are taking on the responsibility for handling the back button. That means that no other on back pressed behavior is going to occur when you get a callback.
If you're using Navigation, you can use your NavController to pop the back stack:
requireActivity().onBackPressedDispatcher.addCallback(this) {
backPressed()
// Now actually go back
findNavController().popBackStack()
}

This works for me in androidx.appcompat:appcompat:1.1.0
requireActivity().onBackPressedDispatcher.addCallback(
this,
object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
Log.d(TAG, "Fragment back pressed invoked")
// Do custom work here
// if you want onBackPressed() to be called as normal afterwards
if (isEnabled) {
isEnabled = false
requireActivity().onBackPressed()
}
}
}
)

You can also remove callback instead of setting enabled if it's no longer needed. I use it with nested graph like this because when you touch back in a nested nav graph with it's NavHostFragment, it removes it from main fragment back stack instead of opening last fragment in nested nav graph.
// Get NavHostFragment
val navHostFragment =
childFragmentManager.findFragmentById(R.id.nested_nav_host_fragment)
// ChildFragmentManager of the current NavHostFragment
val navHostChildFragmentManager = navHostFragment?.childFragmentManager
val callback = object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
val backStackEntryCount = navHostChildFragmentManager!!.backStackEntryCount
if (backStackEntryCount == 1) {
// We are at the root of nested navigation, remove this callback
remove()
requireActivity().onBackPressed()
} else {
navController?.navigateUp()
}
}
}
requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, callback)

unsaved warning on back pressed in fragment

I want to show dialog when user press back or quit from fragment if there are some data unsaved. I am trying to override onbackpressed but unfortunately I got error lateinit property barcodeList has not been initialized. how to solve it?
here is my script on activity:
override fun onBackPressed() {
val theFragment = supportFragmentManager.fragments
for(i in 0 until theFragment.size)
{
if(theFragment[i].tag == "stocker_fragment")
{
StockerFragment().onBackPressed()
}
}
}
and this is in fragment:
fun onBackPressed() {
var check = false
// this barcodeList variable error.
for(i in 0 until barcodeList.size)
{
if(barcodeList[i].barcode.trim()=="")
{
check = true
break
}
}
if (check)
{
AlertHelper(context).onBackPressedAlert()
}
}
FYI: I have initialized barcodeList on onCreateView and everything is fine. only error in onBackPressed.
And my last question is, how do i know if user quit from fragment without pressing back button?

I think the problem is in your onBackPressed() implementation in the Activity. With the line StockerFragment().onBackPressed() you are creating a new instance of the StockerFragment and calling onBackPressed() on it, rather than calling it on the instance that is actively being used.
You should be able to adjust your Activity onBackPressed() like so:
override fun onBackPressed() {
val theFragment = supportFragmentManager.fragments
for(i in 0 until theFragment.size)
{
if(theFragment[i].tag == "stocker_fragment")
{
(theFragment[i] as StockerFragment).onBackPressed()
}
}
}
You can also make this a bit more kotliny like so:
override fun onBackPressed() {
supportFragmentManager.fragments.forEach { fragment ->
if (fragment is StockerFragment) {
fragment.onBackPressed()
}
}
}
You'll probably also want to figure out a way to decide whether the fragment's onBackPressed has determined that the Activity should stick around or not. Then, if the fragment is happy, you should call super.onBackPressed() in the Activity so that the expected back behavior (leave the Activity) happens.