I am using the following fragment to show an onboarding screen on the first launch of the application. Should I inflate my layout in onCreateView or in onViewCreated? I don't quite understand how to decide on this. Also, do I need to create a ViewModel for my code?
class OnBoardingFragment : Fragment() {
private lateinit var viewPager: ViewPager
private lateinit var dotsLayout: LinearLayout
private lateinit var sliderAdapter: SliderAdapter
private lateinit var dots: Array<TextView?>
private lateinit var letsGetStarted: Button
private lateinit var next: Button
private lateinit var animation: Animation
private var currentPos: Int = 0
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val navOptions = NavOptions.Builder().setPopUpTo(R.id.onBoardingFragment, true).build()
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_onboarding, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewPager = view.findViewById(R.id.slider);
dotsLayout = view.findViewById(R.id.dots);
letsGetStarted = view.findViewById(R.id.get_started_btn);
next = view.findViewById(R.id.next_btn)
sliderAdapter = SliderAdapter(requireContext())
viewPager.adapter = sliderAdapter;
addDots(0);
viewPager.addOnPageChangeListener(changeListener);
next.setOnClickListener {
viewPager.currentItem = currentPos + 1
}
letsGetStarted.setOnClickListener {
findNavController().navigate(R.id.action_onBoardingFragment_to_loginFragment)
}
}
private fun addDots(position: Int) {
dots = arrayOfNulls(2)
dotsLayout.removeAllViews();
for (i in dots.indices) {
dots[i] = TextView(requireContext())
dots[i]!!.text = HtmlCompat.fromHtml("•", HtmlCompat.FROM_HTML_MODE_LEGACY)
dots[i]!!.setTextColor(
ContextCompat.getColor(
requireContext(),
android.R.color.darker_gray
)
)
dots[i]!!.textSize = 35F
dotsLayout.addView(dots[i])
}
if (dots.isNotEmpty()) {
dots[position]!!.setTextColor(
ContextCompat.getColor(
requireContext(),
R.color.wine_red
)
)
}
}
private var changeListener: ViewPager.OnPageChangeListener =
object : ViewPager.OnPageChangeListener {
override fun onPageScrolled(
position: Int,
positionOffset: Float,
positionOffsetPixels: Int
) {
}
override fun onPageSelected(position: Int) {
addDots(position)
currentPos = position
animation =
AnimationUtils.loadAnimation(requireContext(), android.R.anim.fade_in)
if (position == 0) {
letsGetStarted.visibility = View.INVISIBLE
next.animation = animation
next.visibility = View.VISIBLE
} else {
letsGetStarted.animation = animation
letsGetStarted.visibility = View.VISIBLE
next.visibility = View.INVISIBLE
}
}
override fun onPageScrollStateChanged(state: Int) {}
}
}`
The Android framework calls Fragment's onCreateView to create the view object hierarchy. Therefore, it's correct to inflate the layout here as you did.
onViewCreated is called afterwards, usually you find views and setup them. So, your code is ok.
Regarding the ViewModel, in your sample code you're just configuring the UI so you won't need it. If instead, you need to obtain some data from an API service, transform it, show the states of "loading data", "data retrieved" and "there was an error retrieving data", then you would like not to do those things in the fragment and you could consider using an MVVM approach.
Some references:
https://developer.android.com/guide/fragments/lifecycle#fragment_created_and_view_initialized
https://guides.codepath.com/android/Creating-and-Using-Fragments
https://developer.android.com/topic/architecture
onCreateView is where you inflate the view hierarchy, and return it (so the Fragment can display it). If you're handling that inflation yourself, you need to override onCreateView so you can take care of it when the system makes that request. That's why it's named that way - when the view (displayed layout) is being created, this function is called, and it provides a View.
onViewCreated is called after the Fragment's view has already been created and provided to it for display. You get a reference to that view passed in, so you can do setup stuff like assigning click listeners, observing View Models that update UI elements, etc. You don't inflate your layout here because it won't be displayed (unless you're explicitly inflating other stuff and adding it to the existing view for some reason, which is more advanced and probably not what you're talking about).
So onCreateView is really concerned with creating a view hierarchy for display, and onViewCreated is for taking that displayed hierarchy and initialising your stuff. You might not need to implement onCreateView at all (e.g. if you use the Fragment constructor that takes a layout ID, so it sets it up for you) in which case you'd just implement onViewCreated instead. Or if you are handling it yourself in onCreateView, and you don't have much setup code, you might run that on the View you've inflated before you return it, and not bother with onViewCreated at all.
It's worth getting familiar with the Fragment lifecycle if you haven't already, just so you know the basic way the system moves between states and the callbacks it calls as it does so (and have a look at the documentation for the callback methods too!)
Related
I'm using a interface to switch from recycler View to details activitas. my interface function works. position is coming. But I can't switch to Details Activity. I think the soproduct is from context. How can I solve this problem? Thank you
class OrderFragment : Fragment() , OnMovieClickListener {
private lateinit var linearLayoutManager: LinearLayoutManager
private lateinit var adapter: RvAdapter
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view : View = inflater.inflate(R.layout.fragment_order, container, false)
val orderApiService = OrderApiService()
val api = orderApiService.getDataa(requireActivity())
api.myOrdersAssigned().enqueue(object : Callback<List<BaseModel>?> {
override fun onResponse(
call: Call<List<BaseModel>?>,
response: Response<List<BaseModel>?>
) {
val arrayOrder = response.body()
val layoutManager: LinearLayoutManager = LinearLayoutManager(activity)
recyclerViewMyOrders.setLayoutManager(layoutManager)
adapter = RvAdapter(arrayOrder as ArrayList<BaseModel>,this#OrderFragment)
recyclerViewMyOrders.setAdapter(adapter)
adapter.notifyDataSetChanged()
if(response.isSuccessful){
response.body()?.let {
}
}
}
override fun onFailure(call: Call<List<BaseModel>?>, t: Throwable) {
print(t.message.toString())
}
})
return view
}
override fun onMovieItemClicked(position: Int) {
println("Clicked : " + position.toString())
val intent = Intent(requireContext().applicationContext,DetailsActivity::class.java)
startActivity(intent)
}
}
My Interface Function :
override fun onMovieItemClicked(position: Int) {
println("Clicked : " + position.toString())
val intent = Intent(requireContext().applicationContext,DetailsActivity::class.java)
startActivity(intent)
}
Create your variable Context inside your Fragment like this :
private Context context;
Than you initialize it inside onCreateView like this :
context = view.getContext();
And insite you functio, instead of calling requireContext().applicationContext as parameter, call context
The code in on Java but you can easily convert it to Kotlin
I have a question first: why don't you use the DetailFragment instead of a whole new Activity (because your OrderFragment and Detail can be both in a single Activity)
Still want to use Activity
On your interface's override method, try to change requireContext().applicationContext to requireContext() only. Please reply me your println works or not.
Change to Fragment
I know 2 ways to move to another fragment programmatically:
parentFragmentManager.beginTransaction()
.replace<DestinationFragment>(R.id.fragmentContainer)
findNavController().navigate(action) // if you are using Navigation Components
P/s:
I'm also a Android newbie and I see something can be improved in your source code, please correct me if I have something wrong
Adapter and LinearLayoutManager don't have to be a class's property because you no longer need to use them outside API call, so just change their scope to inside onResponse()
I have suffered from doing things with view in onCreateView() (because they are not fully inflated yet ?), so considering move your logic to onViewCreated() for a safe bet.
I am using nested recyclerview.
In the picture, the red box is the Routine Item (Parent Item), and the blue box is the Detail Item (Child Item) in the Routine Item.
You can add a parent item dynamically by clicking the ADD ROUTINE button.
Similarly, child items can be added dynamically by clicking the ADD button of the parent item.
As a result, this function works just fine.
But the problem is in the code I wrote.
I use a ViewModel to observe and update parent item addition/deletion.
However, it does not observe changes in the detail item within the parent item.
I think it's because LiveData only detects additions and deletions to the List.
So I put _items.value = _items.value code to make it observable when child items are added and deleted.
This way, I didn't even have to use update code like notifyDataSetChanged() in the child adapter.
In the end it is a success, but I don't know if this is the correct code.
Let me know if you have additional code you want!
In Fragment.kt
class WriteRoutineFragment : Fragment() {
private var _binding : FragmentWriteRoutineBinding? = null
private val binding get() = _binding!!
private lateinit var adapter : RoutineAdapter
private val vm : WriteRoutineViewModel by viewModels { WriteRoutineViewModelFactory() }
override fun onCreateView(inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?): View? {
_binding = FragmentWriteRoutineBinding.inflate(inflater, container, false)
adapter = RoutineAdapter(::addDetail, ::deleteDetail)
binding.rv.adapter = this.adapter
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
getTabPageResult()
// RecyclerView Update
vm.items.observe(viewLifecycleOwner) { updatedItems ->
adapter.setItems(updatedItems)
}
}
private fun getTabPageResult() {
val navController = findNavController()
navController.currentBackStackEntry?.also { stack ->
stack.savedStateHandle.getLiveData<String>("workout")?.observe(
viewLifecycleOwner, Observer { result ->
vm.addRoutine(result) // ADD ROUTINE
stack.savedStateHandle?.remove<String>("workout")
}
)
}
}
private fun addDetail(pos: Int) {
vm.addDetail(pos)
}
private fun deleteDetail(pos: Int) {
vm.deleteDetail(pos)
}
}
ViewModel
class WriteRoutineViewModel : ViewModel() {
private var _items: MutableLiveData<ArrayList<RoutineModel>> = MutableLiveData(arrayListOf())
val items: LiveData<ArrayList<RoutineModel>> = _items
fun addRoutine(workout: String) {
val item = RoutineModel(workout, "TEST")
_items.value?.add(item)
// _items.value = _items.value
}
fun addDetail(pos: Int) {
val detail = RoutineDetailModel("TEST", "TEST")
_items.value?.get(pos)?.addSubItem(detail) // Changing the parent item's details cannot be observed by LiveData.
_items.value = _items.value // is this right way?
}
fun deleteDetail(pos: Int) {
if(_items.value?.get(pos)?.getSubItemSize()!! > 1)
_items.value?.get(pos)?.deleteSubItem() // is this right way?
else
_items.value?.removeAt(pos)
_items.value = _items.value // is this right way?
}
}
This is pretty standard practice when using a LiveData with a mutable List type. The code looks like a smell, but it is so common that I think it's acceptable and people who understand LiveData will understand what your code is doing.
However, I much prefer using read-only Lists and immutable model objects if they will be used with RecyclerViews. It's less error prone, and it's necessary if you want to use ListAdapter, which is much better for performance than a regular Adapter. Your current code reloads the entire list into the RecyclerView every time there is any change, which can make your UI feel laggy. ListAdapter analyzes automatically on a background thread your List for which items specifically changed and only rebinds the changed items. But it requires a brand new List instance each time there is a change, so it makes sense to only use read-only Lists if you want to support using it.
I'm trying to populate a spinner with data using room, I'm getting no errors but my spinner isn't displaying anything. I think it might have something to do with how I'm calling initFirstUnitSpinnerData() in my onCreateView method? But I'm having no luck. I'm using kotlin.
Thanks in advance.
DAO:
#Query("SELECT firstUnit FROM conversion_table WHERE category LIKE :search")
fun getByCategory(search: String): LiveData<List<String>>
Repository:
fun getByCategory(search: String): LiveData<List<String>>{
return conversionsDAO.getByCategory(search)
}
View Model:
fun getByCategory(search: String): LiveData<List<String>> {
return repository.getByCategory(search)
}
Fragment:
class UnitsFragment : Fragment() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
private lateinit var mConversionsViewModel: ConversionsViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(R.layout.fragment_units, container, false)
mConversionsViewModel = ViewModelProvider(this).get(ConversionsViewModel::class.java)
initFirstUnitSpinnerData()
return view
}
private fun initFirstUnitSpinnerData() {
val spinnerFirstUnit = view?.findViewById<Spinner>(R.id.firstUnitSpinner)
if (spinnerFirstUnit != null) {
val allConversions = context?.let {
ArrayAdapter<Any>(it, R.layout.support_simple_spinner_dropdown_item)
}
mConversionsViewModel.getByCategory("Distance")
.observe(viewLifecycleOwner, { conversions ->
conversions?.forEach {
allConversions?.add(it)
}
})
spinnerFirstUnit.adapter = allConversions
spinnerFirstUnit.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
override fun onItemSelected(
parent: AdapterView<*>?,
view: View?,
position: Int,
id: Long
) {
Toast.makeText(requireContext(), "$allConversions", Toast.LENGTH_LONG).show()
}
override fun onNothingSelected(parent: AdapterView<*>?) {
}
}
}
}
}
This is the kind of thing you should debug really - click on the left gutter for the first line of initFirstUnitSpinnerData (the val spinnerFirstUnit one), click the Debug App button up near the Run one, and it'll pause when it hits that breakpoint you added.
Then you can move through, step by step, looking at the values of stuff and checking if it looks right, and how the code executes. It's a super useful thing to learn and it'll save you a lot of headaches!
Anyway I'm guessing your problem is that you're calling initFirstUnitSpinnerData from inside onCreateView - the latter is called by the Fragment when it needs its layout view inflating, which you do and then return it to the Fragment.
So inside initFirstUnitSpinnerData, when you reference view (i.e. the Fragment's view, which it doesn't have yet, because onCreateView hasn't returned it yet) you're getting a null value. So spinnerFirstUnit ends up null, and when you null check that, it skips setting up the adapter.
Override onViewCreated (which the Fragment calls when it has its layout view) and call your function from there, it'll be able to access view then - see if that helps!
I am using a gridlayout in a fragment on which the user can switch the amount of items shown per line (by pressing a button he can switch currently between 6 and 4 but might extend on adding a third option).
When the user leaves the the fragment (switches to another fragment) and comes back later, I want to retain the information of how many items per line are shown.
After having tried different options (savedInstanceState: doesn't work as the activity is never recreated, getArguments: not a feasible option afaik, as I have to pass the information several times) I am using a sharedViewModel that is implemented anyways as some of information is observed.
I feel like it's an overkill, as it is "just" an int (or even a bool, if there are just 2 states) and there might be a more simple ("built in"?) solution which might be similiar to activity's savedInstanceState.
Here is some code:
Fragment with GridLayout
class LibraryFragment : Fragment() {
private val model: SharedViewModel by activityViewModels()
private lateinit var gridlayoutManager: GridLayoutManager
private lateinit var thumbnailAdapter: ThumbnailAdapter
private lateinit var thumbnailRecyclerView: RecyclerView
private var booksPerLine = 4
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
_binding = FragmentLibraryViewerBinding.inflate(layoutInflater)
val view = libraryFragmentBinding.root
initRecyclerView()
return view
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
model.booksPerLine.observe(viewLifecycleOwner, Observer {
booksPerLine = it
switchNoOfBooksPerLine()
})
}
private fun initRecyclerView() {
thumbnailRecyclerView = libraryFragmentBinding.thumbnailRecyclerView
switchNoOfBooksPerLine()
thumbnailAdapter = ThumbnailAdapter { selectedBook: Book -> displaySelectedBook(selectedBook) }
thumbnailAdapter.setThumbnailList(listOf())
thumbnailRecyclerView.adapter = thumbnailAdapter
}
private fun switchNoOfBooksPerLine() {
gridlayoutManager = GridLayoutManager(requireContext(), booksPerLine, LinearLayoutManager.VERTICAL, false)
thumbnailRecyclerView.layoutManager = gridlayoutManager
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
return when (item.itemId) {
R.id.change_grid -> {
when (booksPerLine) {
4 -> model.setBooksPerLine(6)
6 -> model.setBooksPerLine(4)
}
true
}
}
}
}
SharedViewModel with grid information
class SharedViewModel : ViewModel() {
val booksPerLine = MutableLiveData<Int>()
internal fun setBooksPerLine(_booksPerLine: Int) {
booksPerLine.value = _booksPerLine
}
}
So the questions is, if there is a more simple/efficient way of retaining the Int? (bonus question: how efficient (in terms of ressource usage like memory) is a SharedViewModel actually?
Is there a built in method like savedInstanceState for activities for fragments, too?
I would suggest to keep the data in the activity. And in fragment get the data from activity in onViewCreated method like-
val data = (activity as MyActivity)?.data
Also, put back the data into the activity the other way when data changed-
(activity as MyActivity)?.data = changedData
This is the manual way. Keep in mind the data is nullable.
I'm trying to refresh the data in my fragment every time the user clicks on it in the Bottom Menu Navigation. I already wrote an interface which gets called each time the fragment gets selected by the user
The problem is that the method inside my fragment has no access to the view of the fragment (I guess):
MainMenu
viewPager = findViewById(R.id.frame_container)
viewPager!!.offscreenPageLimit = 5
viewPager!!.orientation = ViewPager2.ORIENTATION_HORIZONTAL
viewPager!!.adapter = pageAdapter
viewPager!!.currentItem = 0
viewPager!!.isUserInputEnabled = false
viewPager!!.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
override fun onPageSelected(position: Int) {
super.onPageSelected(position)
if(position == 2) {
val mFragment = ListFragment()
mFragment.ready(this#MainMenu)
}
}
})
The Interface "Ready":
interface ReadyInterface {
fun ready(activity: FragmentActivity?)
}
and the ListFragment:
class ListFragment: Fragment(), ReadyInterface {
var mView : View? = null
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.fragment_list, container, false)
this.mView = view
val user = FirebaseAuth.getInstance().currentUser
return if (user != null) {
view
} else {
val unregisteredView = inflater.inflate(R.layout.fragment_unregistred, container, false)
val registerNow = unregisteredView.findViewById<TextView>(R.id.textview_registernow)
unregisteredView
}
override fun ready(activity: FragmentActivity?) {
testText = mView!!.findViewById(R.id.test_text)
testText.text = "Test Text here"
Toast.makeText(activity!!.applicationContext,"Test",Toast.LENGTH_LONG).show()
}
This code here crashes with a "kotlin.KotlinNullPointerException" on line "testText.text = ...."
So I guess the fun ready hasn't got access to the view of my fragment because of the fragments lifecycle, am I right? How could I fix this?
There is no need to implement interface here. You can directly make ready() a member function of ListFragment and call it from onPageSelected(position: Int) in MainMenuActivity. Currently, the interface method is being called before onCreateView() causing it to throw null pointer exception as the view is not initialised yet.
You are creating a new instance of ListFragment() while calling ready on it. This new fragment is not attached to the ViewPager. This new instance also has not gone through any lifecycle methods, therefore, it's view is not yet initialized. Due to this, you get a NullPointerException while calling methods on a view.
To solve this you can instead fetch the current fragment from the ViewPager and call your method on it.