i have 1 Activity with 3 Fragments. (A, B and C). So,
Activity -> FragmentContainerView with fragment A
<androidx.fragment.app.FragmentContainerView
android:id="#+id/host_fragment"
android:name="cl.gersard.shoppingtracking.ui.product.list.ListProductsFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="ListProductsFragment" />
Fragment A has a button to go to Fragment B
Fragment A -> Fragment B (with addToBackStack)
Then, i go to from Fragment B to Fragment C
Fragment B -> Fragment C (without addToBackStack)
i need when i save a item in Fragment C, come back to Fragment A, so i dont use addToBackStack.
The problem is when in Fragment C i use
requireActivity().supportFragmentManager.popBackStack()
or
requireActivity().onBackPressed()
the Fragment A appears but the method OnViewCreated in Fragment C is called so execute a validations that i have in that Fragment C.
I need from Fragment C come back to Fragment A without calling OnViewCreated of Fragment C
Code of interest
MainActivity
fun changeFragment(fragment: Fragment, addToBackStack: Boolean) {
val transaction = supportFragmentManager.beginTransaction()
.replace(R.id.host_fragment, fragment,fragment::class.java.simpleName)
if (addToBackStack) transaction.addToBackStack(null)
transaction.commit()
}
Fragment A (ListProductsFragment)
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
setupRecyclerView()
observeLoading()
observeProducts()
viewModel.fetchProducts()
viewBinding.btnEmptyProducts.setOnClickListener { viewModel.fetchProducts() }
viewBinding.fabAddPurchase.setOnClickListener { addPurchase() }
}
private fun addPurchase() {
(requireActivity() as MainActivity).changeFragment(ScanFragment.newInstance(),true)
}
Fragment B (ScanFragment)
override fun barcodeDetected(barcode: String) {
if (processingBarcode.compareAndSet(false, true)) {
(requireActivity() as MainActivity).changeFragment(PurchaseFragment.newInstance(barcode), false)
}
}
Fragment C (PurchaseFragment)
private fun observePurchaseState() {
viewModel.purchasesSaveState.observe(viewLifecycleOwner, { purchaseState ->
when (purchaseState) {
is PurchaseSaveState.Error -> TODO()
is PurchaseSaveState.Loading -> manageProgress(purchaseState.isLoading)
PurchaseSaveState.Success -> {
Toast.makeText(requireActivity(), getString(R.string.purchase_saved_successfully), Toast.LENGTH_SHORT).show()
requireActivity().supportFragmentManager.popBackStack()
}
}
})
}
The full code is here https://github.com/gersard/PurchaseTracking
OK, I think I see your issue. You are conditionally adding things to the backstack which put the fragment manager in a weird state.
Issue
You start on Main, add the Scanner to the back stack, but not the Product. So when you press back, you're popping the Scanner off the stack but the Product stays around in the FragmentManager. This is why get a new instance each and every time you scan and go back. Why this is happening is not clear to me - seems like maybe an Android bug? You are replacing fragments so it's odd that extra instances are building up.
One Solution
Change your changeFragment implementation to conditionally pop the stack instead of conditionally adding things to it.
fun changeFragment(fragment: Fragment, popStack: Boolean) {
if (keepStack) supportFragmentManager.popBackStack()
val transaction = supportFragmentManager.beginTransaction()
.replace(R.id.host_fragment, fragment,fragment::class.java.simpleName)
transaction.addToBackStack(null) // Always add the new fragment so "back" works
transaction.commit()
}
Then invert your current logic that calls changeFragment:
private fun addPurchase() {
// Pass false to not pop the main activity
(requireActivity() as MainActivity)
.changeFragment(ScanFragment.newInstance(), false)
}
And ...
override fun barcodeDetected(barcode: String) {
if (processingBarcode.compareAndSet(false, true)) {
// Pass true to pop the barcode that's currently there
(requireActivity() as MainActivity)
.changeFragment(PurchaseFragment.newInstance(barcode), true)
}
}
Related
I have couple of fragments (lets say A,B and C) replacing each other. In fragment A, there is a recyclerView which should be updated as an observer receives changes in a liveData. But the observer does not receive updates when I move to fragment B because fragment A is already destroyed.
I have changed the the lifeCycle owner from viewLifeCycleOwner to this (fragment) but still the same result.
Here is some snippet of my code:
class MainActivity: AppCompatActivity() {
val fragments = listOf(fragmentA(), fragmentB(), fragmentC())
private fun moveToFragment(index: Int) {
if (fragments.isNotEmpty()) {
viewModel.selectedPage = index
val transaction = supportFragmentManager.beginTransaction()
transaction.replace(R.id.fragment_container, fragments[index])
transaction.commit()
}
}
}
class FragmentA(): Fragment{
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
fragmentAViewModel.listOfThings.observe(viewLifecycleOwner) { things ->
things?.let {
when (things.status) {
Status.SUCCESS -> {
thingsAdapter.submitList(things.data)
}
else -> {
thingsAdapter.submitList(emptyList())
}
}
}
}
}
I know that "replace" destroys the fragments but I also tried using HIDE/SHOW fragments but this pattern overlays fragments on top of each other and I wasn't able to get it fixed.
My question is what the best practice is here to make sure that the observer/recyclerView is already updated before going to the fragment. Otherwise the recyclerView will have old values and they change in few milliseconds after I go the fragmentA. The most obvious situation is when the recyclerView is supposed to be empty but when I go to fragmentA items are still there for a moment before they disappear.
I have a Home fragment with multiple buttons and when I click the Contact button, another fragment is opened. Inside this fragment I have two child fragments and two buttons, and I can switch between those child fragments using those buttons. The problem is when I press the Back Button, it switches back between child fragments and only after that it goes back to Home fragment, but I want to directly go back to Home Fragment.
This is how I'm opening the child fragments:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val contactsListFragment = ContactsListFragment()
val groupsListFragment = GroupsListFragment()
activity?.title = getString(R.string.contacts_and_groups)
openChildFragment(contactsListFragment)
binding.contactsButton.setOnClickListener {
openChildFragment(contactsListFragment)
}
binding.groupsButton.setOnClickListener {
openChildFragment(groupsListFragment)
}
}
private fun openChildFragment(fragment: Fragment) {
val childFragmentManager = childFragmentManager
val transaction: FragmentTransaction = childFragmentManager.beginTransaction()
transaction.replace(binding.contactsGroupsFl.id, fragment)
transaction.addToBackStack(null)
transaction.commit()
}
If anyone can help me with this issue would be great. Thanks!
I think you should add a listener for the back button in both of your fragments so that you can clear all the backstack when it's pressed. Something like this :
requireActivity().onBackPressedDispatcher.addCallback(
viewLifecycleOwner,
object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
for (i: Int in 1..parentFragmentManager.backStackEntryCount) {
parentFragmentManager.popBackStack()
}
}
})
I have an activity with two fragments added to it using :
fun addFragment(fragment: Fragment){
private val fragmentManager = supportFragmentManager
val fragmentTag = fragment::class.simpleName.toString()
val ft = fragmentManager.beginTransaction()
ft.add(R.id.fragments_container, fragment,fragmentTag)
ft.addToBackStack(fragmentTag)
ft.commit()
}
I add two fragments A and B to activity with this order:
A ---> B
when i press back button on phone it return from B to A as expected
but the problem is that when i call activity's onBackPressed method when clicking on a view for example:
imgBack.setOnClickListener {
onBackPressed()
}
it does not work like when i press back button on the phone
it returns to fragment A but not showing fragment A views as expected.
onBackPressed:
override fun onBackPressed() {
if (fragmentManager.backStackEntryCount > 1) {
fragmentManager.popBackStack()
} else {
finish()
}
}
if you imgBack are in fragmentB call
imgBack.setOnClickListener {
activity?.onBackPressed()
}
There is a huge bug I am trying to figure out in my latest project using Kotlin. So how the app works is that it has a Bottom Navigation Activity, and on click on the icons on the Bottom menu, it replaces the container with the respected fragment. On onCreate of the activity, I instantiate all the different fragments with a function defined in a companionObject within the fragments, which returns itself (kind of like a static factory method in java):
override fun onCreate(savedInstanceState: Bundle?) {
{...}
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)
fragment1 = Fragment1.newInstance()
fragment2 = Fragment2.newInstance()
}
Then I have this switch to replace the container to the respected fragment on click:
private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.f1 -> {
replaceFragment(fragment1)
return#OnNavigationItemSelectedListener true
}
R.id.f2 -> {
replaceFragment(fragment2)
return#OnNavigationItemSelectedListener true
}
}
false
}
{...}
fun replaceFragment(destFragment: Fragment) {
supportFragmentManager
.beginTransaction()
.replace(R.id.container, destFragment)
.addToBackStack(destFragment.toString())
.commit()
}
The fragments are communicating. If you where to click on both fragments, and thereby cause their lifecycles to execute, the code works fine. However, if you do changes in frag1, invoking a communication between the fragments, without having clicked on frag2 in advance, the app crashes. The reason is this line in frag2:
fun saveList(){
val sharedpref : SharedPreferences = context!!.getSharedPreferences("sharedPrefs", MODE_PRIVATE)
{...}
}
Turns out that the context is null, if the user has never invoked the frag2 lifecycle by clicking it. Any ideas to how to fix this problem?
Use Activity context for these case
fun saveList() {
activity?.let {
val sharedpref: SharedPreferences =
it.getSharedPreferences("sharedPrefs", MODE_PRIVATE)
{ }
}
}
Android Studio 3.4
I have a simple stock forecast app that uses single activity called ForecastActivity and 3 fragments called LoadingFragment, ForecastFragment, and RetryFragment
The RetryFragment will be added first using the following code in the
`ForecastActivity`:
private fun startRetryFragment() {
fragmentManager?.let {
val fragmentTransaction = it.beginTransaction()
fragmentTransaction.replace(R.id.forecastActivityContainer, RetryFragment(), "RetryFragment")
fragmentTransaction.commit()
}
}
I have a button in the RetryFragment that will start the ForecastActivity again.
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
btnRetry.setOnClickListener {
startActivity(Intent(activity, ForecastActivity::class.java))
}
}
Then the LoadingFragment will start using this code in the ForecastActvity
private fun startLoadingFragment() {
fragmentManager?.let {
val fragmentTransaction = it.beginTransaction()
fragmentTransaction.replace(R.id.forecastActivityContainer, LoadingFragment(), "LoadingFragment")
fragmentTransaction.commit()
}
}
Then after loading has completed the ForecatActivity will start the ForecastFragment
private fun startForecastFragment() {
fragmentManager?.let {
val fragmentTransaction = it.beginTransaction()
fragmentTransaction.replace(R.id.forecastActivityContainer, RetryFragment(), "ForecastFragment")
fragmentTransaction.commit()
}
In my ForecastActivity I am trying to remove the fragments from the backstack, basically, from here I just want to finish the app. However, as I didn't add any to the backstack I don't expect the count to greater than zero. However, I was wondering how can I end the app and prevent the RetryFragment displaying again?
override fun onBackPressed() {
fragmentManager?.let {
if(it.backStackEntryCount > 0) {
it.popBackStackImmediate()
}
else {
super.onBackPressed()
}
}
}
However, when I click the back from when I am on the ForecastFragment I expect the application to finish. However, the RetryFragment is displayed and then I have to click the back button again to end the app.
Is there something wrong doing this in the RetryFragment
Basically, I just want to go back to the ForecastActivity from the RetryFragment to start again.
startActivity(Intent(activity, ForecastActivity::class.java))
Many thanks for any suggestions.
I think your issue is that you're re-launching the ForecastActivity again from the RetryFragment. If you restructure your code so that the RetryFragment can trigger a retry function in ForecastActivity, you could just replace the RetryFragment with the next appropriate fragment instead of calling startActivity() to create a new ForecastActivity.