I have a simple activity with a BottomNavigationView. I'm using fragments to implement the contents of the activity for the different pages.
When the user presses the back button, it's supposed to go back to the previously looked at page. The problem is, when you repeatedly switch back and forth between the pages (fragments), this entire history is recorded. Take this example:
A -> B -> A -> B -> C -> A -> C
Pressing the back button would result in the reverse, but instead I want this behaviour (I noticed it in the Instagram app):
C -> A -> B -> Exit App
So every fragment should only have one entry in the backstack. How do I do this? I do I remove the previous transactions for a fragment from the stack?
Is this at all possible using a FragmentManager? Or do I have to implement my own?
My Activity with the BottomNavigationView:
class ActivityOverview : AppCompatActivity() {
// Listener for BottomNavigationView
private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_home -> {
// "Home" menu item pressed
setActiveFragment(resources.getString(R.string.tag_fragment_home))
return#OnNavigationItemSelectedListener true
}
R.id.navigation_dashboard -> {
// "Dashboard" menu item pressed
return#OnNavigationItemSelectedListener true
}
R.id.navigation_settings -> {
// "Settings" menu item pressed
setActiveFragment(resources.getString(R.string.tag_fragment_settings))
return#OnNavigationItemSelectedListener true
}
}
false
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_overview)
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)
navigation.menu.findItem(R.id.navigation_home).setChecked(true)
// Set initial fragment
setActiveFragment(resources.getString(R.string.tag_fragment_home))
}
override fun onBackPressed() {
// > 1 so initial fragment addition isn't removed from stack
if (fragmentManager.backStackEntryCount > 1) {
fragmentManager.popBackStack()
} else {
finish()
}
}
// Update displayed fragment
fun setActiveFragment(tag: String) {
val fragment = if (fragmentManager.findFragmentByTag(tag) != null) {
// Fragment is already initialized
if (fragmentManager.findFragmentByTag(tag).isVisible) {
// Fragment is visible already, don't add another transaction
null
} else {
// Fragment is not visible, add transaction
fragmentManager.findFragmentByTag(tag)
}
} else {
// Fragment is not initialized yet
when (tag) {
resources.getString(R.string.tag_fragment_home) -> FragmentHome()
resources.getString(R.string.tag_fragment_settings) -> FragmentSettings()
else -> null
}
}
if (fragment != null) {
val transaction = fragmentManager.beginTransaction()
transaction.replace(R.id.container_fragment, fragment, tag)
transaction.addToBackStack(null)
transaction.commit()
}
}
}
At this point I'm pretty sure it doesn't work with FragmentManager, so I created a class to implement a stack that doesn't allow duplicates:
class NoDuplicateStack<T> {
val stack: MutableList<T> = mutableListOf()
val size: Int
get() = stack.size
// Push element onto the stack
fun push(p: T) {
val index = stack.indexOf(p)
if (index != -1) {
stack.removeAt(index)
}
stack.add(p)
}
// Pop upper element of stack
fun pop(): T? {
if (size > 0) {
return stack.removeAt(stack.size - 1)
} else {
return null
}
}
// Look at upper element of stack, don't pop it
fun peek(): T? {
if (size > 0) {
return stack[stack.size - 1]
} else {
return null
}
}
}
I then integrated this class into my activity:
class ActivityOverview : AppCompatActivity() {
val fragmentsStack = NoDuplicateStack<String>()
val fragmentHome = FragmentHome()
val fragmentSettings = FragmentSettings()
val fragmentHistory = FragmentHistory()
// Listener for BottomNavigationView
private val mOnNavigationItemSelectedListener = ...
override fun onCreate(savedInstanceState: Bundle?) {
...
}
override fun onBackPressed() {
if (fragmentsStack.size > 1) {
// Remove current fragment from stack
fragmentsStack.pop()
// Get previous fragment from stack and set it again
val newTag = fragmentsStack.pop()
if (newTag != null) {
setActiveFragment(newTag)
}
} else {
finish()
}
}
// Update displayed fragment
fun setActiveFragment(tag: String) {
val fragment = when (tag) {
resources.getString(R.string.tag_fragment_home) -> fragmentHome
resources.getString(R.string.tag_fragment_settings) -> fragmentSettings
resources.getString(R.string.tag_fragment_history) -> fragmentHistory
else -> null
}
if (fragment != null && !fragment.isVisible) {
fragmentManager.beginTransaction()
.replace(R.id.container_fragment, fragment, tag)
.commit()
fragmentsStack.push(tag)
}
}
}
I also faced the same problem, I did this which uses the system stack
val totalFragments = supportFragmentManager.backStackEntryCount
if (totalFragments != 0) {
val removed = supportFragmentManager.getBackStackEntryAt(totalFragments - 1)
poppedFragments.add(removed.name!!)
for (idx in totalFragments - 1 downTo 0) {
val fragment = supportFragmentManager.getBackStackEntryAt(idx)
if (!poppedFragments.contains(fragment.name)) {
supportFragmentManager.popBackStack(fragment.name, 0)
return
}
}
finish()
return
}
super.onBackPressed()
and then added this while launching the fragment
if (poppedFragments.contains(tag)) {
poppedFragments.remove(tag)
}
Related
We have implemented bottom navigation as described here:
https://developer.android.com/guide/navigation/navigation-ui#bottom_navigation
https://medium.com/androiddevelopers/navigation-multiple-back-stacks-6c67ba41952f
We are using navigation version 2.4.1, which supports multiple backstacks out of the box. This saves fragment state so that in navigating from main fragment A -> B -> C -> B using the bottomnav, state of fragment B is saved and restored upon return. This is as intended and much requested behaviour.
However, for one of the fragments in our bottomnav menu, I would like the possibility to NOT save the state. This is due to some confusing behaviour when navigating using talkback. Is there a way in the navigation framework to set a flag to not save state for a single fragment? Or any other way to programmatically clear savedstate without actually doing so "manually" by resetting the UI elements in fragment onDestroy/onResume or similar?
What I did was just use the same androidx.navigation.ui.NavigationUI.setupWithNavController logic but change the saveState and other logic specific to my use case. You could apply this when navigating to one specific fragment.
this.findViewById<BottomNavigationView>(R.id.bottom_navigation).apply {
setOnItemSelectedListener { item ->
val builder = NavOptions.Builder().setLaunchSingleTop(true)
val destinationId = item.itemId
item.isChecked = true
if (
navController.currentDestination!!.parent!!.findNode(item.itemId)
is ActivityNavigator.Destination
) {
builder.setEnterAnim(R.anim.nav_default_enter_anim)
.setExitAnim(R.anim.nav_default_exit_anim)
.setPopEnterAnim(R.anim.nav_default_pop_enter_anim)
.setPopExitAnim(R.anim.nav_default_pop_exit_anim)
} else {
builder.setEnterAnim(R.animator.nav_default_enter_anim)
.setExitAnim(R.animator.nav_default_exit_anim)
.setPopEnterAnim(R.animator.nav_default_pop_enter_anim)
.setPopExitAnim(R.animator.nav_default_pop_exit_anim)
}
if (item.order and Menu.CATEGORY_SECONDARY == 0) {
builder.setPopUpTo(
navController.graph.findStartDestination().id,
inclusive = false,
saveState = false
)
}
val options = builder.build()
return#setOnItemSelectedListener try {
navController.navigate(destinationId, null, options)
// Return true only if the destination we've navigated to matches the MenuItem
(navController.currentDestination?.id ?: false) == destinationId
} catch (e: IllegalArgumentException) {
false
}
}
// Do nothing on reselect
setOnItemReselectedListener {}
val weakReference = WeakReference(this)
navController.addOnDestinationChangedListener(
object : NavController.OnDestinationChangedListener {
override fun onDestinationChanged(
controller: NavController,
destination: NavDestination,
arguments: Bundle?
) {
// Hide BottomNavigationView from top level fragments
if (topLevelDestinations.any { it == destination.id }) {
this#apply.visibility = View.VISIBLE
} else this#apply.visibility = View.GONE
// Highlight item in BottomNavigationView
val view = weakReference.get()
if (view == null) {
navController.removeOnDestinationChangedListener(this)
return
}
view.menu.forEach { item ->
if (destination.id == item.itemId) {
item.isChecked = true
}
}
}
})
}
I am using a ViewPager having 2 pages. First page of that ViewPager is MainFragment. MainFragment has ViewPager as bottomNavigationView. Each page has a FragmentContainerView and By default they contains HomeFragment, CommunityFragment and NotificationFragment respectively.
This is the Source Code and this is the APK of the project. So you can test it and improve it easily.
Now if i am in HomeFragment and I click on a profile button so It transact to ProfileFragment and from there setting and so on. And on clicking on back button it get back perfectly one-by-one. But it does not happens same with other FragmentContainerView. Even they get back directly to the parent fragment. Overall i am unable to handle the backstack between different ViewPagers and fragments.
To avoid the confusion of FragmentContainers i transact it like this
val containerId = (view?.parent as ViewGroup).id
activity?.supportFragmentManager?.beginTransaction()?.add(containerId, profileFragment)?.addToBackStack(null)?.commit()
Now the handling of BackPressed() in MainActivity is here
if (view_pager_main_activity?.currentItem == 0)
{
if (view_pager_main_fragment?.currentItem == 0)
{
val recyclerView = findViewById<RecyclerView>(R.id.recycler_view_home)
val appbarHome = findViewById<AppBarLayout>(R.id.appbar_home)
val layoutManager = recyclerView?.layoutManager as LinearLayoutManager
when {
layoutManager.findFirstCompletelyVisibleItemPosition() == 0 -> {
super.onBackPressed()
}
supportFragmentManager.backStackEntryCount != 0 -> {
supportFragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE)
}
else -> {
layoutManager.scrollToPositionWithOffset(0, 0)
appbarHome.setExpanded(true)
//recyclerView.smoothScrollToPosition(0)
}
}
}
else
{
// Otherwise, select the previous step.
view_pager_main_fragment?.setCurrentItem(view_pager_main_fragment.currentItem - 1, false)
}
}
else
{
// Otherwise, select the previous step.
view_pager_main_activity?.currentItem = view_pager_main_activity.currentItem - 1
}
I checked your code and the problem was the usage of
supportFragmentManager.popBackStack(null,FragmentManager.POP_BACK_STACK_INCLUSIVE)
If you read the description of the flag POP_BACK_STACK_INCLUSIVE it says:
If set, and the name or ID of a back stack entry has been supplied,
then all matching entries will be consumed until one that doesn't
match is found or the bottom of the stack is reached. Otherwise, all
entries up to but not including that entry will be removed.
So it was removing the multiple entries at once.
The reason it worked for Home screen was that it never reached that case. It always went in the first case of:
layoutManager.findFirstCompletelyVisibleItemPosition() == 0 -> {
super.onBackPressed()
}
And that's what you exactly need for your case just call super.onBackPressed() when you want to pop only one fragment at once. So your final code becomes like this:
In your MainActivity's onBackPressed()
override fun onBackPressed() {
if (view_pager_main_activity?.currentItem == 0) {
if (view_pager_main_fragment?.currentItem == 0) {
val recyclerView = findViewById<RecyclerView>(R.id.listRecyclerView)
val appbarHome = findViewById<AppBarLayout>(R.id.appbar_home)
val layoutManager = recyclerView?.layoutManager as LinearLayoutManager
when {
layoutManager.findFirstCompletelyVisibleItemPosition() == 0 -> {
super.onBackPressed()
}
//This is never reached. It can be removed
supportFragmentManager.backStackEntryCount != 0 -> {
supportFragmentManager.popBackStack(
null,
FragmentManager.POP_BACK_STACK_INCLUSIVE
)
}
else -> {
layoutManager.scrollToPositionWithOffset(0, 0)
appbarHome.setExpanded(true)
//recyclerView.smoothScrollToPosition(0)
}
}
} else if (supportFragmentManager.backStackEntryCount != 0) {
super.onBackPressed()
} else {
// Otherwise, select the previous step.
view_pager_main_fragment?.setCurrentItem(
view_pager_main_fragment.currentItem - 1,
false
)
}
} else if (supportFragmentManager.backStackEntryCount != 0) {
super.onBackPressed()
} else {
// Otherwise, select the previous step.
view_pager_main_activity?.currentItem = view_pager_main_activity.currentItem - 1
}
}
Edit 1: From the comments
I want to clear the backstack when bottom nav selection changes.
If you want to clear the selection when you change the bottom navigation selection changes then you've to set a listener and clear the back stack in your MainFragment as following:
view?.bottomNavView?.setOnNavigationItemSelectedListener { item ->
//check if item is being re-selected then just return and don't do anything
if (bottomNavView.selectedItemId == item.itemId){
return#setOnNavigationItemSelectedListener false
}
//if the bottom nav item selection changes then clear the back stack of previous tab
parentFragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE)
when (item.itemId) {
R.id.homeFragment -> viewPager2.setCurrentItem(0, false)
R.id.searchFragment -> viewPager2.setCurrentItem(1, false)
R.id.notificationsFragment -> viewPager2.setCurrentItem(2, false)
}
true
}
And the rest can remain same. Try this out and do let me know.
On my action, I use the onBackPressed() method. When I compare the fragment that triggered the event, the id is never the same and always falls into the else-statement. What's wrong?
override fun onBackPressed() {
val navHost = this.supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
val pressed = navHost?.childFragmentManager.fragments?.get(0) as IOnBackPressed
var currentFragment = navHost?.childFragmentManager.fragments?.get(0)
pressed?.onBackPressed()?.takeIf { it }?.let {
when (currentFragment.id) {
R.id.myfragmet -> {
// implementation
}
else -> {
super.onBackPressed()
}
}
}
}
I want to know from what fragment I returning when I press the back button, so that I can do the necessary action. Let me simplify the code:
override fun onBackPressed() {
// get the nav host in the action
val navHost = this.supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
// get the current fragment in the nav host
var currentFragment = navHost?.childFragmentManager.fragments?.get(0)
// Verify the fragment to do a action
when (currentFragment.id) {
R.id.myfragmet -> {
// implementation
}
else -> {
super.onBackPressed()
}
}
}
But the currentFragment.Id is never equals R.id.myfragemnt
I have a problem switching between fragments using my bottom navigation view.it loads first and i can switch between the fragments for the first time but if a fragment was already loaded and try to navigate back to it. My app crashes showing an error i listed below.
Here is my code
private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener{
when (it.itemId) {
R.id.vegetables -> {
showFragment(VegetablesFragment(),VegetablesFragment().javaClass.simpleName)return#OnNavigationItemSelectedListener true
}
R.id.fruits -> {
showFragment(FruitsFragment(),FruitsFragment().javaClass.simpleName)
return#OnNavigationItemSelectedListener true
}
R.id.grocery -> {
showFragment(GroceryFragment(),GroceryFragment().javaClass.simpleName)
return#OnNavigationItemSelectedListener true
}
else -> return#OnNavigationItemSelectedListener false
}
}
private fun showFragment(fragment : Fragment ,fragmentName :String) {
val transaction = manager.beginTransaction()
val currentFragment = manager.primaryNavigationFragment
if (currentFragment != null) {
transaction.hide(currentFragment)
}
val fragmentTemp = manager.findFragmentByTag(fragmentName)
if (fragmentTemp == null){
transaction.add(R.id.fragmentHolder,fragment,fragmentName)
Log.d("ac1001","case 2")
} else {
Log.d("ac1001","case 1")
transaction.show(fragment)
}
transaction.setPrimaryNavigationFragment(fragment)
transaction.setReorderingAllowed(true)
transaction.commitNowAllowingStateLoss()
}
Error:
java.lang.IllegalArgumentException: Fragment VegetablesFragment{d4a075d (f9739b50-c0fc-47c1-80d1-dc413ffd5a09)} is not an active fragment of FragmentManager FragmentManager{5b1a8d2 in HostCallbacks{2810da3}}
I tried searching everywhere but couldn't find an answer.
The error is occuring on my transaction.show(..)
Thanks in advance.
Try with this code. change your showFragment function to ->
fun showFragment(fragment: Fragment ,fragmentName :String) {
val transaction = supportFragmentManager.beginTransaction()
transaction.replace(R.id.fragmentHolder, fragment)
transaction.addToBackStack(fragmentName)
transaction.commit()
}
Hope this will help you.
Fixed it by changing my code to:
private fun showFragment(fragment : Fragment ,fragmentName :String) {
val transaction = manager.beginTransaction()
val currentFragment = manager.primaryNavigationFragment
if (currentFragment != null) {
transaction.hide(currentFragment)
}
val fragmentTemp = manager.findFragmentByTag(fragmentName)
if (fragmentTemp == null){
transaction.add(R.id.fragmentHolder,fragment,fragmentName)
} else {
transaction.show(fragmentTemp)
}
transaction.setPrimaryNavigationFragment(fragmentTemp)
transaction.setReorderingAllowed(true)
transaction.commitNowAllowingStateLoss()
}
I have set of Fragments navigates inside activity. While I called findFragmentByTag() the fragments onCreateView() and onViewCreated() are called again and the data is reset to normal. how to prevent the recreation of fragment?
You can have look on the code of the advanced navigation in android samples
fun BottomNavigationView.setupWithNavController(
navGraphIds: List<Int>,
fragmentManager: FragmentManager,
containerId: Int,
intent: Intent): LiveData<NavController> {
// Map of tags
val graphIdToTagMap = SparseArray<String>()
// Result. Mutable live data with the selected controlled
val selectedNavController = MutableLiveData<NavController>()
var firstFragmentGraphId = 0
// First create a NavHostFragment for each NavGraph ID
navGraphIds.forEachIndexed { index, navGraphId ->
val fragmentTag = getFragmentTag(index)
// Find or create the Navigation host fragment
val navHostFragment = obtainNavHostFragment(
fragmentManager,
fragmentTag,
navGraphId,
containerId
)
// Obtain its id
val graphId = navHostFragment.navController.graph.id
if (index == 0) {
firstFragmentGraphId = graphId
}
// Save to the map
graphIdToTagMap[graphId] = fragmentTag
// Attach or detach nav host fragment depending on whether it's the selected item.
if (this.selectedItemId == graphId) {
// Update livedata with the selected graph
selectedNavController.value = navHostFragment.navController
attachNavHostFragment(fragmentManager, navHostFragment, index == 0)
} else {
detachNavHostFragment(fragmentManager, navHostFragment)
}
}
// Now connect selecting an item with swapping Fragments
var selectedItemTag = graphIdToTagMap[this.selectedItemId]
val firstFragmentTag = graphIdToTagMap[firstFragmentGraphId]
var isOnFirstFragment = selectedItemTag == firstFragmentTag
// When a navigation item is selected
setOnNavigationItemSelectedListener { item ->
// Don't do anything if the state is state has already been saved.
if (fragmentManager.isStateSaved) {
false
} else {
val newlySelectedItemTag = graphIdToTagMap[item.itemId]
if (selectedItemTag != newlySelectedItemTag) {
// Pop everything above the first fragment (the "fixed start destination")
fragmentManager.popBackStack(firstFragmentTag,
FragmentManager.POP_BACK_STACK_INCLUSIVE)
val selectedFragment = fragmentManager.findFragmentByTag(newlySelectedItemTag)
as NavHostFragment
// Exclude the first fragment tag because it's always in the back stack.
if (firstFragmentTag != newlySelectedItemTag) {
// Commit a transaction that cleans the back stack and adds the first fragment
// to it, creating the fixed started destination.
fragmentManager.beginTransaction()
.attach(selectedFragment)
.setPrimaryNavigationFragment(selectedFragment)
.apply {
// Detach all other Fragments
graphIdToTagMap.forEach { _, fragmentTagIter ->
if (fragmentTagIter != newlySelectedItemTag) {
detach(fragmentManager.findFragmentByTag(firstFragmentTag)!!)
}
}
}
.addToBackStack(firstFragmentTag)
.setCustomAnimations(
R.anim.nav_default_enter_anim,
R.anim.nav_default_exit_anim,
R.anim.nav_default_pop_enter_anim,
R.anim.nav_default_pop_exit_anim)
.setReorderingAllowed(true)
.commit()
}
selectedItemTag = newlySelectedItemTag
isOnFirstFragment = selectedItemTag == firstFragmentTag
selectedNavController.value = selectedFragment.navController
true
} else {
false
}
}
}
// Optional: on item reselected, pop back stack to the destination of the graph
setupItemReselected(graphIdToTagMap, fragmentManager)
// Handle deep link
setupDeepLinks(navGraphIds, fragmentManager, containerId, intent)
// Finally, ensure that we update our BottomNavigationView when the back stack changes
fragmentManager.addOnBackStackChangedListener {
if (!isOnFirstFragment && !fragmentManager.isOnBackStack(firstFragmentTag)) {
this.selectedItemId = firstFragmentGraphId
}
// Reset the graph if the currentDestination is not valid (happens when the back
// stack is popped after using the back button).
selectedNavController.value?.let { controller ->
if (controller.currentDestination == null) {
controller.navigate(controller.graph.id)
}
}
}
return selectedNavController
}
this example code you can find the full code here
https://github.com/android/architecture-components-samples/tree/master/NavigationAdvancedSample