So I have an activity with DrawerLayout. I can switch to Fragment1 which contains TabLayout with three other fragments (NestedFragment1, NestedFragment2, NestedFragment3). I want to be able to save data in each NestedFragments since I make API calls inside them. I tried to override onSaveInstanceState and save the data but SavedInstanceState was always null.
Fragment1 code:
class Fragment1 : Fragment() {
private lateinit var viewPager: ViewPager
private lateinit var tabLayout: TabLayout
private lateinit var pagerAdapter: PagerAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
pagerAdapter = ForecastPagerAdapter(childFragmentManager)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.fragment_forecast, container, false)
viewPager = view.findViewById(R.id.view_pager)
viewPager.offscreenPageLimit = 3
viewPager.adapter = pagerAdapter
tabLayout = view.findViewById(R.id.tabs)
tabLayout.setupWithViewPager(viewPager)
return view
}
}
Example of nested fragment code:
class NestedFragment : Fragment() {
private lateinit var recyclerView: RecyclerView
private lateinit var recyclerViewAdapter: HourForecastAdapter
private lateinit var swipeRefreshLayout: SwipeRefreshLayout
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
recyclerViewAdapter = HourForecastAdapter()
}
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view = inflater!!.inflate(R.layout.fragment_day_forecast, container, false)
swipeRefreshLayout = view.findViewById(R.id.swipe_refresh_layout_hour)
swipeRefreshLayout.apply {
this.setOnRefreshListener {
performQuery()
}
}
recyclerView = view.findViewById(R.id.recycler_view_hour_forecast)
recyclerView.adapter = recyclerViewAdapter
recyclerView.layoutManager = LinearLayoutManager(activity)
return view
}
fun performQuery() {
// ...
recyclerViewAdapter.forecastList = result.hourly.data
recyclerViewAdapter.notifyDataSetChanged()
}
}
I want to save forecastList (List) which is returned by performQuery method. Every time I switch to Fragment 1 all data from nested fragments is gone.
This is the code used for switching fragments:
navigationView.setNavigationItemSelectedListener {
var fragment = when (it.itemId) {
R.id.nav_map -> Fragment0()
R.id.nav_forecast -> Fragment1()
R.id.nav_app_info -> Fragment2()
else -> Fragment1()
}
replaceFragment()
it.isChecked = true
drawerLayout.closeDrawers()
true
}
}
Edit: added function for fragment replacement:
fun replaceFragment(fragment: android.support.v4.app.Fragment){
val fragmentName = fragment::class.java.simpleName
val isFragmentInBackStack = fragmentManager.popBackStackImmediate(fragmentName, 0)
if (!isFragmentInBackStack) {
fragmentManager.beginTransaction()
.replace(R.id.main_activity_frame, fragment)
.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE)
.addToBackStack(fragmentName)
.commit()
}
}
First, you have to call .addToBackstack(null) before you commit your transaction. This will affect your back-button also.
See #documentation:
Add this transaction to the back stack. This means that the transaction will be remembered after it is committed, and will reverse its operation when later popped off the stack.
Why this works this way? Your application doesn't known you want to open old fragment instead of creating new one (because you actually asked for creating new fragment). Also, you have to tell your application - "Ey, you! Don't create new fragment, but get the old one from backstack if there is any".
You can check how to do it fe. here: How to resume Fragment from BackStack if exists
PS: It's good practice to creating fragment not by constructor, but by static method "getInstance(): Fragment".
So I managed to solve this problem by using fragment "caching":
fun cacheFragment(fragment: android.support.v4.app.Fragment) {
Log.d("Caching", "Working with ${fragment.javaClass.simpleName}")
var findFragment = supportFragmentManager.findFragmentByTag(fragment.javaClass.simpleName)
if (findFragment == null) {
Log.d("Caching", "Creating new instance of ${fragment.javaClass.simpleName}")
findFragment = fragment.javaClass.newInstance()
}
supportFragmentManager.beginTransaction()
.replace(R.id.main_activity_frame, findFragment, fragment.javaClass.simpleName)
.addToBackStack(null)
.commit()
}
When a user selects an item from nav bar, we check if the fragment already exists in the back stack and then we can reuse it.
Related
i am currently programming an app in Android Studio and i am having a big issue. The main problem is, that i want an activity with a fragment in it and this fragment has got a spinner. I wanted to find the spinner by id, but it always returned null and i read that i can't use findViewById if it is not in the ContentView i just set. So i am currently trying to find the fragment that contains the spinner, but i also can't find the fragment, i tried findFragmentById and findViewById from the FragmentManager. I always get a TypeCastException and if i try findFragmentById(...)!! it throws a NullPointer.
This is my MainActivity:
class MainActivity : AppCompatActivity() {
private val manager: FragmentManager? = supportFragmentManager
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
showDeviceFragment()
val fragment = manager!!.findFragmentById(R.id.fragment_holder) as DeviceFragment
val options = arrayOf("Wandhalterung (Arm)", "Gestellhalterung (Arm)", "Gestellhalterung")
fragment.option.adapter = ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, options)
}
fun showDeviceFragment() {
val transaction = manager!!.beginTransaction()
val fragment = DeviceFragment()
transaction.add(R.id.fragment_holder, fragment, "DEVICE_FRAGMENT")
transaction.addToBackStack(null)
transaction.commit()
}
}
And this is the DeviceFragment:
class DeviceFragment : Fragment() {
lateinit var option : Spinner
companion object {
fun newInstance(): DeviceFragment {
return DeviceFragment()
}
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(R.layout.fragment_device, container, false)
option = view.spinner
return inflater?.inflate(R.layout.fragment_device, container, false)
}
}
The fragment_holder just is a FrameLayout.
Thanks in advance
Few things:
1) No need to hold reference for supportFragmentManager, use it directly (because i am not sure if it will be null when Activity is initialized)
2) Try removing addToBackStack(null) and using findFragmentByTag("DEVICE_FRAGMENT")
3) Most importantly, Don't try to access "things" of Fragment from Activity, do those Adapter initialization/fill in the Fragment itself. Because Fragment has its own lifecycle and you may try to access "things" at wrong lifecycle
In my application, I have a ViewPager2 and a TabLayout. The app is composed of 4 tabs. The 3rd one dynamically loads a list fragment.
I have a problem opening the 4th tab, but only when I didn't opened the 3rd one before.
By example, this will crash:
Open app, show 1st tab. Click on 4th tab. => App will crash with following error:
java.lang.IllegalArgumentException: No view found for id 0x7f080105 (my.package:id/root_frame) for fragment ListFragment{6190d6d (6304bfad-1db2-464d-a524-7e3450243bcc) id=0x7f080105}
But if I proceed as following:
Open app, show 1st tab. Click on 3rd tab. Click on 4th tab. => App won't crash.
It looks like when I change tab, it "swipe" through all tabs between the current tab and the clicked one, causing fragments to start initialising.
Here's the code of the 3rd fragment:
class ListRootFragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
return inflater.inflate(R.layout.list_root_fragment, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val transaction = fragmentManager!!.beginTransaction()
transaction.replace(R.id.root_frame, ListFragment.newInstance())
transaction.commit()
}
companion object {
fun newInstance(): ListRootFragment {
val fragment = ListRootFragment()
val args = Bundle()
fragment.arguments = args
return fragment
}
}
}
My ListFragment:
class ListFragment : Fragment() {
lateinit var globalData: GlobalData
private lateinit var listView: ListView
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
globalData = (this.activity as ContentActivity).globalData
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View { // Inflate the layout for this fragment
val rootView: View =
inflater.inflate(R.layout.fragment_list, container, false)
listView = rootView.findViewById<ListView>(R.id.categoriesList)
val categoriesList = globalData.getCategories()
val adapter = this.getActivity()?.applicationContext?.let { CategoryAdapter(it, categoriesList) }
listView.adapter = adapter
listView.setOnItemClickListener { _, _, position, _ ->
// ...
}
return rootView
}
companion object {
fun newInstance(): ListFragment {
val fragment = ListFragment()
val args = Bundle()
fragment.arguments = args
return fragment
}
}
}
Here's the code of my ViewPagerAdapter:
class ViewPagerAdapter(fragmentActivity: FragmentActivity) :
FragmentStateAdapter(fragmentActivity) {
override fun createFragment(position: Int): Fragment {
return when(position){
0 -> HomeFragment.newInstance()
1 -> MapViewFragment.newInstance()
2 -> ListRootFragment.newInstance()
3 -> MoreFragment.newInstance()
else -> HomeFragment.newInstance()
}
}
override fun getItemCount(): Int {
return TAB_COUNT
}
companion object {
private const val TAB_COUNT = 4
}
}
And the Activity that contains the view pager:
class ContentActivity : AppCompatActivity() {
lateinit var globalData: GlobalData
lateinit var viewPager: ViewPager2
lateinit var tabLayout: TabLayout
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_content)
globalData = applicationContext as GlobalData
viewPager = findViewById(R.id.pager)
tabLayout = findViewById(R.id.tab_layout)
viewPager.setAdapter(createCardAdapter())
viewPager.isUserInputEnabled = false
TabLayoutMediator(tabLayout, viewPager,
TabConfigurationStrategy { tab, position ->
when (position) {
0 -> tab.text = "Home"
1 -> tab.text = "Map"
2 -> tab.text = "List"
3 -> tab.text = "More"
else -> tab.text = "undefined"
}
}).attach()
}
private fun createCardAdapter(): ViewPagerAdapter? {
return ViewPagerAdapter(this)
}
}
Is there a way to prevent tabs 2+3 to load when going from 1 to 4 or, if not, how can I prevent this error ?
EDIT / WORKAROUND:
Ok so I found a workaround for this bug. Instead of using a combinaison of ViewPager2 and TabLayout, I now use a BottomNavigation for the exact same result, but without the swiping effect.
In my case it works because I only need 4 tabs, but for more complex apps with more tabs, it wouldn't work, so if anyone knows how to fix it...
To disable smoothScroll, use another TabLayoutMediator constructor:
TabLayoutMediator(tabLayout, viewPager, /*autoRefresh=*/ true, /* smoothScroll= */false
TabConfigurationStrategy { tab, position ->
//...
}
}).attach()
I have a fragment class that contains a ViewPager with two sites. These sites contain a few widgets like CheckBoxes and I want them to stay checked when the orientation changes.
MainFragment:
class StatsFragment: Fragment() {
private val fragmentStatsCat = StatsCategoryFragment()
private val fragmentStatsMon = StatsMonthFragment()
private lateinit var pager: ViewPager
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view: View = inflater.inflate(R.layout.fragment_stats, container, false)
pager = view.findViewById(R.id.stats_container)
val pagerAdapter = StatsScreenSlidePagerAdapter(childFragmentManager)
pager.adapter = pagerAdapter
return view
}
private inner class StatsScreenSlidePagerAdapter(fm: FragmentManager): FragmentStatePagerAdapter(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {
override fun getItem(position: Int): Fragment {
return if (position == 0) {
fragmentStatsCat
} else {
fragmentStatsMon
}
}
override fun getCount(): Int = 2
override fun saveState(): Parcelable? {
return null
}
}
}
One of the ViewPagerFragments:
class StatsMonthFragment: Fragment() {
companion object {
private const val CHECKBOX_KEY = "isChecked"
private const val CATEGORY_KEY = "category"
}
private lateinit var btnPrevCat: ImageButton
private lateinit var btnNextCat: ImageButton
private lateinit var cbAllCats: CheckBox
private lateinit var categories: List<Category>
private var i: Int = 0
private var isCbChecked: Boolean? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
if(savedInstanceState != null) {
i = savedInstanceState.getInt(CATEGORY_KEY)
isCbChecked = savedInstanceState.getBoolean(CHECKBOX_KEY)
}
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.fragment_stats_months, container, false)
btnNextCat = view.findViewById(R.id.btn_next_cat)
btnPrevCat = view.findViewById(R.id.btn_prev_cat)
cbAllCats = view.findViewById(R.id.cb_all_cats)
categories = DatabaseInitializer.getInstance().getAllCategories(AppDatabase.getInstance(context).categoryDao())
if(isCbChecked == null || isCbChecked!!) {
val initFragment = StatsSelectedFilterFragment() //This is just a fragment with a TextView; I use fragments for that for the CustomAnimations
initFragment.setText(categories[i].cat_name)
childFragmentManager.beginTransaction().add(R.id.container_stats_categories, initFragment).commit()
} else {
val fragment = StatsSelectedFilterFragment()
fragment.setText(getString(R.string.all_categories))
childFragmentManager.beginTransaction()
.replace(R.id.container_stats_categories, fragment)
.commit()
}
btnNextCat.setOnClickListener {
val fragment = StatsSelectedFilterFragment()
fragment.setText(categories[i].cat_name)
childFragmentManager.beginTransaction()
.setCustomAnimations(R.anim.slide_in_right, R.anim.slide_out_left)
.replace(R.id.container_stats_categories, fragment)
.commit()
}
btnPrevCat.setOnClickListener {
val fragment = StatsSelectedFilterFragment()
fragment.setText(categories[i].cat_name)
childFragmentManager.beginTransaction()
.setCustomAnimations(R.anim.slide_in_left, R.anim.slide_out_right)
.replace(R.id.container_stats_categories, fragment)
.commit()
}
cbAllCats.setOnCheckedChangeListener{_,checked->
if(checked) {
val fragment = StatsSelectedFilterFragment()
fragment.setText(getString(R.string.all_categories))
childFragmentManager.beginTransaction()
.replace(R.id.container_stats_categories, fragment)
.commit()
} else {
val fragment = StatsSelectedFilterFragment()
fragment.setText(categories[i].cat_name)
childFragmentManager.beginTransaction()
.replace(R.id.container_stats_categories, fragment)
.commit()
}
}
return view
}
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
val isAllCatsChecked = cbAllCats.isChecked
outState.putBoolean(CHECKBOX_KEY, isAllCatsChecked)
outState.putInt(CATEGORY_KEY, i)
}
}
Now on every screen rotation, the fragment gets recreated twice, first with savedInstanceState != null and then with savedInstanceState == null, which means that I don't have access to the old settings in the Fragments. As I know, it is because the fragment gets recreated, and then the MainFragment containing the viewpager gets also recreated, which means that the fragments within the viewPager get created a second time. I have tried something like this in the MainFragment:
private lateinit var fragmentStatsCat: StatsCategoryFragment
private lateinit var fragmentStatsMon: StatsMonthFragment
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
if(savedInstanceState == null) {
fragmentStatsMon = StatsMonthFragment()
fragmentStatsCat = StatsCategoryFragment()
} else {
//Finding old fragments
}
}
Maybe this would solve the problem (I am not sure), but I don't know how I can find the fragments, as they are inside a ViewPager.
EDIT
I have now found a solution to find the fragments when the activity is recreated:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
if(savedInstanceState == null)
{
fragmentStatsMon = StatsMonthFragment()
fragmentStatsCat = StatsCategoryFragment()
} else {
fragmentStatsMon = childFragmentManager.getFragment(savedInstanceState, FRAG_MONTH_TAG) as StatsMonthFragment
fragmentStatsCat = childFragmentManager.getFragment(savedInstanceState, FRAG_CAT_TAG) as StatsCategoryFragment
}
}
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
childFragmentManager.putFragment(outState, FRAG_CAT_TAG, fragmentStatsCat)
childFragmentManager.putFragment(outState, FRAG_MONTH_TAG, fragmentStatsMon)
}
This puts a reference in the Bundle with which I can get the fragment afterwards. But now, I have another problem. When the activity is recreated, it throws the following exception:
java.lang.IllegalStateException: Fragment already added: StatsCategoryFragment{f06ec65 (a1991f39-3af4-4a74-9aeb-79274beae04a) id=0x7f09014a}
I don't know how to solve that because I don't really manually add the fragments. Also, I don't really get it because the viewpager and the adapter also get recreated, don't they? So why are the fragments still attached to the adapter?
I also don't know in which line of code this happens, I could neither find it out in the logcat nor by debugging.
Put this line in AndroidManifest.xml in the entry of your Activity in which you are loading your Fragments:
android:configChanges="layoutDirection|keyboardHidden|orientation|screenSize"
By this, Data will not be reset when your Fragment is recreated by any condition.
Example:
<activity
android:name=".activity.MainActivity"
android:configChanges="layoutDirection|keyboardHidden|orientation|screenSize"
android:label="#string/app_name"></activity>
Check out this similar question
https://www.google.com/url?sa=t&source=web&rct=j&url=https://stackoverflow.com/questions/15313598/once-for-all-how-to-correctly-save-instance-state-of-fragments-in-back-stack&ved=2ahUKEwja6rasobzjAhVh1uAKHRakDXIQFjAAegQIBhAB&usg=AOvVaw0Hg_vwSnBayxV1EJfKOUZk
I have an Activity with a ViewPager containing Fragments that are summoned with custom buttons. Currently, my custom adapter's getItem method is being called, but the pager is going blank rather than going to the new fragment
Here is my adapter :
class ScreenSlidePagerAdapter(fragmentManager: FragmentManager) : FragmentStatePagerAdapter(fragmentManager) {
private val NUM_FRAGMENTS = 2
override fun getCount(): Int = NUM_FRAGMENTS
override fun getItem(position: Int): Fragment {
var fragment: Fragment = WelcomeFragment.newInstance()
when (position) {
0 -> fragment = WelcomeFragment.newInstance()
1 -> fragment = LanguageSelectFragment.newInstance()
}
println(position)
return fragment
}
}
Here is the method that gets called on button click. The views are given a tag corresponding to their Fragment's position in the adapter, and this is retrieved on click to pull up the right fragment.
private fun switchScreens(view: View) {
val fragment = mPagerAdapter.getItem(view.getTag().toString().toInt())
val fragmentManager = supportFragmentManager
val fragmentTransaction = fragmentManager.beginTransaction()
fragmentTransaction.replace(R.id.main_view_pager, fragment)
fragmentTransaction.commit()
}
And my fragment:
class LanguageSelectFragment : Fragment() {
private var listener: OnFragmentInteractionListener? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_language_select, container, false)
}
fun onButtonPressed(uri: Uri) {
listener?.onFragmentInteraction(uri)
}
override fun onAttach(context: Context) {
super.onAttach(context)
if (context is OnFragmentInteractionListener) {
listener = context
} else {
}
}
override fun onDetach() {
super.onDetach()
listener = null
}
interface OnFragmentInteractionListener {
fun onFragmentInteraction(uri: Uri)
}
companion object {
#JvmStatic
fun newInstance() =
LanguageSelectFragment().apply {
arguments = Bundle().apply {
}
}
}
}
Do you have a ViewPager container for your framgents ?
If yes, that's not the way to use the pagerAdapter. You should see this link. It's in Java but you can easily adapt it to kotlin.
If no, I'm not sure what you are trying to do but I think the
ViewPager is what you need.
If you just want to switch fragments on a click, just use a FrameLayout to display the fragment you want and switch between them with transactions. I'm not familiar with kotlin but something like this should work.
private fun switchScreens(i: Integer) {
val fragment;
when (i) {
0 -> fragment = WelcomeFragment.newInstance()
1 -> fragment = LanguageSelectFragment.newInstance()
}
val fragmentManager = supportFragmentManager
val fragmentTransaction = fragmentManager.beginTransaction()
fragmentTransaction.replace(R.id.main_view_pager, fragment)
fragmentTransaction.commit()
}
If you want to slide to one fragment to another, you can use a ViewPager (see the link above).
Best
I want to create a dialog which contain's ViewPager inside it which have 3 pages and all pages have different layout structure. I want a solution by that i can set the layout content programmatically . I think this can be done by making fragments for each page but i don't know how to do this.
I go through these answers but i am not getting idea how to use them in my case.
Viewpager in Dialog?
ViewPager in Custom Dialog
ViewPager in simple Dialog
You can try and build your custom dialog through DialogFragment. Consider the XML layout would contain a ViewPager and the code to go about would be:
class PagerDialog : DialogFragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
return inflater.inflate(R.layout.element_fragment_pager_dialog, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
setupPager()
}
private fun setupPager() {
val pagerFragment1 = PagerFragment1.newInstance()
val pagerFragment2 = PagerFragment2.newInstance()
val pagerFragment3 = PagerFragment3.newInstance()
viewPager?.adapter = MyFragmentPagerAdapter(childFragmentManager).apply {
adapterReference = object : PageAdapterInterface {
override var fragmentList: List<Fragment> =
mutableListOf(pagerFragment1, pagerFragment2, pagerFragment3)
}
}
}
companion object {
const val tag = "PagerDialog"
}
}
I have used reference to the list because it might cause leaks when not handled correctly. So the PagerAdapterInterface would look like:
interface PageAdapterInterface {
var fragmentList: List<Fragment>
fun getItemCount() = fragmentList.size
#Throws(StackOverflowError::class)
fun getItemAt(index: Int) : Fragment {
if (index >= fragmentList.size) throw StackOverflowError()
return fragmentList[index]
}
}
Your view pager adapter can make use of this reference in manner that is accessing referentially like:
class MyFragmentPagerAdapter(childFragmentManager: FragmentManager) : FragmentStatePagerAdapter(childFragmentManager){
lateinit var adapterReference: PageAdapterInterface
override fun getItem(p0: Int): Fragment = adapterReference.getItemAt(p0)
override fun getCount(): Int = adapterReference.getItemCount()
}
Finally in your Activity or Fragment on create() or onViewCreated() functions respectively, you can initialize the dialog as shown:
class MyActivity: AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
// use childFragmentManager if the code is
// used within the Fragment
val prev = supportFragmentManager.findFragmentByTag(PagerDialog.tag)
if (prev != null) {
supportFragmentManager.beginTransaction()
.remove(prev)
.addToBackStack(null)
.commit()
}
PagerDialog().show(supportFragmentManager, PagerDialog.tag)
}
}
Note: DialogFragment is deprecated on > API 28 check out https://developer.android.com/reference/android/app/DialogFragment