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How to get data from fragment to activity? [duplicate]

This question already has answers here:
Passing data between a fragment and its container activity
(16 answers)
Closed 1 year ago.
How to correctly transfer data from a fragment to an activity? I do as follows:
1- Create an interface
interface IProfileToActivity {
fun profileInfo(data: AllHeroes.Global)
}
2- Then I inheritance in the activity
class ProfileActivity : AppCompatActivity(), IProfileToActivity {
private lateinit var myBinding: ActivityProfileBinding
override fun profileInfo(data: AllHeroes.Global) {
myBinding.tvUsername.text = data.name
myBinding.tvDivision.text = data.rank.rankName
Log.i("Apex Info 3", data.toString())
}
}
3- sending from a fragment
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
(activity as? IProfileToActivity)?.profileInfo(allInfoApexResponse.global)
mHeroesAdapter.heroesList(allAdapterListHero)
}
but nothing happens, why? what did I do wrong?

You need not create an interface here. You can use requireActivity() to get a reference to the parent activity. Using it you can access public fields and functions of you activity.
class ProfileActivity : AppCompatActivity() {
private lateinit var myBinding: ActivityProfileBinding
fun profileInfo(data: AllHeroes.Global) {
myBinding.tvUsername.text = data.name
myBinding.tvDivision.text = data.rank.rankName
Log.i("Apex Info 3", data.toString())
}
}
And in your fragment:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
(requireActivity as ProfileToActivity).profileInfo(allInfoApexResponse.global)
mHeroesAdapter.heroesList(allAdapterListHero)
}

There are many ways to pass data from fragment to activity:
Using shared ViewModel.
A ViewModel is used to manage and store UI related data in a
lifecycle conscious way.
~Read more
class SharedViewModel: ViewModel() {
private val currItems: MutableLiveData<List<Item>> =
MutableLiveData<List<Item>>(listOf())
fun getCurrItem(): LiveData<List<Item>> {
return currItems
}
fun sendCurrItems(items: MutableList<Item>) {
currItems.postValue(items)
}
}
class ItemFragment: Fragment() {
private val sharedModel: SharedViewModel by activityViewModels()
}
MainActivity: AppCompactActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val model = ViewModelProvider(this).get(SharedViewModel::class.java)
}
}
In the above class, data is being stored and updated using an MutableList. Thing to be noted here is, the above class is a singleton class, i.e. once it is created, it gets destroyed only when the activity is ended.
Let us assume that an item has to be shared from a ItemFragment to the MainActivity
One callback has to be implemented the MainActivity. For that, one can use an Interface
interface ItemListener{
fun sendItem(item : MutableList<Item>)
}
ItemFragment:
class ItemFragment: Fragment() {
override fun sendItems(items: MutableList<Item>?) {
// Send an Item from here as well as update it
}
// Or just simply call sendItem method.
}
MainActivity:
class MainActivity: AppCompactActivity(){
fun receiveItem(context : Context){
private var mCallback: ItemListener? = null
mCallback = context
}
}

How to implement a BaseActivity in mvvm architecture? Without using dependency Injection

I am currently learning MVVM architecture.
I tried to make a BaseActivity class.
My BaseActivity:
abstract class BaseActivity<ViewModel : BaseViewModel, Binding : ViewDataBinding> :
AppCompatActivity(),
EventListener {
lateinit var binding: Binding
private var viewModel: ViewModel? = null
override fun onCreate(savedInstanceState: Bundle?, persistentState: PersistableBundle?) {
super.onCreate(savedInstanceState, persistentState)
binding = DataBindingUtil.setContentView(this, layoutid)
this.viewModel = viewModel ?: getViewModel()
binding.setVariable(getBindingVariable(), viewModel)
binding.executePendingBindings()
}
#get: LayoutRes
abstract val layoutid: Int
abstract fun getViewModel(): ViewModel
abstract fun getBindingVariable(): Int
private fun getViewModelClass(): Class<ViewModel> {
val type = (javaClass.genericSuperclass as ParameterizedType).actualTypeArguments[0]
return type as Class<ViewModel>
}
}
Now I am using this BaseActivity in my SplashActivity:
class SplashActivity : BaseActivity<SplashActivityViewModel, ActivitySplashBinding>() {
private lateinit var viewModel: SplashScreenViewModel
override fun onFailure(message: String) {}
override fun onStarted() {}
override fun onSuccess() {}
override fun getViewModel(): SplashActivityViewModel {
viewModel = ViewModelProvider(this).get(SplashActivityViewModel::class.java)
return viewModel
}
override fun getBindingVariable(): Int {
return BR.splash_viewmodel
}
override val layoutid: Int
get() = R.layout.activity_splash
}
I have used following answer as a reference to implement my BaseActivity.kt: https://stackoverflow.com/questions/55289334/how-to-have-generic-viewmodel-in-baseactivty-class
But I am getting a blank white screen while running the app.
Can someone please tell me what is the problem here or how to make this BaseActivity (without using dependency injection)?

you have overridden the wrong onCreate
override fun onCreate(savedInstanceState: Bundle?) {
I did play around with something like that few years ago, you can find my approach here

How to use abstraction with ViewBinding with base activity?

I was making a base class so that all bindings for child will be set in base
I have done till this
abstract class BaseActivity2<B : ViewBinding?, T : BaseViewModel?> : AppCompatActivity() {
private var viewBinding: B? = null
private var baseViewModel: T? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
}
but am unable to get a way to bind view in oncreat()
generally we bind layout in view binding as
binding = ActivityLoginBinding.inflate(layoutInflater)
setContentView(binding.root)
but i am looking for generalized way in base activity

You can declare a lambda property in the constructor to create the binding object
abstract class BaseActivity<B : ViewBinding>(val bindingFactory: (LayoutInflater) -> B) : AppCompatActivity() {
private lateinit var binding: B
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = bindingFactory(layoutInflater)
setContentView(binding.root)
}
}
You can also define binding as lazy property
private val binding: B by lazy { bindingFactory(layoutInflater) }
Then you need to override nothing in your activities
class MainActivity : BaseActivity<ActivityMainBinding>(ActivityMainBinding::inflate)

Other answer will also solve problem but I would like to do in a clean way.
My Base Class
abstract class BaseVMActivity<VM : ViewModel, B : ViewBinding> : BaseActivity() {
lateinit var viewModel: VM
lateinit var binding: B
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel = ViewModelProvider(this, factory).get(getViewModelClass())
binding = getViewBinding()
setContentView(binding.root)
}
private fun getViewModelClass(): Class<VM> {
val type = (javaClass.genericSuperclass as ParameterizedType).actualTypeArguments[0]
return type as Class<VM>
}
abstract fun getViewBinding(): B
}
My activity:
class MainActivity : BaseVMActivity<AppViewModel, ActivityMainBinding>() {
override fun getViewBinding() = ActivityMainBinding.inflate(layoutInflater)
}
Now I can directly access viewModel or binding:
fun dummy(){
binding.bvReport.text = viewModel.getReportText()
}

It's cleaner to override binding object getter inside the child activity I think. So:
abstract class VBActivity<VB : ViewBinding> : AppCompatActivity() {
protected abstract val binding: VB
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(binding.root)
}
}
And lets say MainActivity will be something like:
class MainActivity : VBActivity<ActivityMainBinding>() {
override val binding get() = ActivityMainBinding.inflate(layoutInflater)
}

State Management with ViewModel on Android when on a flow

Basically I have a state management system using ViewModel that looks like this:
class ViewModelA: ViewModel() {
private val repository: RepositoryA by inject()
private val _stateLiveData = MutableLiveData<ViewState>()
val stateLiveData: LiveData<ViewState> get() = _stateLiveData
private val _eventLiveData = SingleLiveEvent<ViewEvent>()
val eventLiveData: LiveData<ViewEvent> get() = _eventLiveData
private val exceptionHandler = CoroutineExceptionHandler { _, _ ->
_stateLiveData.postValue(ViewState.Error)
}
fun loadList() {
if (_stateLiveData.value is ViewState.Loading) return
launch(exceptionHandler) {
_stateLiveData.run {
value = ViewState.Loading
value = repository.getDocumentList().let {
if (it.isEmpty()) ViewState.Error
else ViewState.Data(it)
}
}
}
}
}
But whenever I am sharing a ViewModel with several Fragments, it becomes bigger and bigger. I am looking for a solution for this, because I don't want to centralize all the logic for an entire application flow inside a ViewModel and I also don't want to pass arguments here and there all the time.
PS: Sorry about my bad english.
Edit: Clarify a bit the question.

I didn't quite understand your question. However, if your question was as follows:
How can I share the same ViewModel Object and use it inside multiple Fragments.
You can check the documentation of ViewModelProvider which is a utility class that provides ViewModels for a specific scope like Activity.
Following is an example code of the usage of ViewModelProvider within two Fragments that will be created and used in the same Activity object:
// An example ViewModel
class SharedViewModel : ViewModel() {
val intLiveData = MutableLiveData<Int>() // an example LiveData field
}
// the first fragment
class Fragment1 : Fragment() {
private lateinit var viewModel: SharedViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel = requireActivity().let { activity ->
ViewModelProvider(activity).get(SharedViewModel::class.java)
}
}
}
// the other fragment
class Fragment2 : Fragment() {
private lateinit var viewModel: SharedViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel = requireActivity().let { activity ->
ViewModelProvider(activity).get(SharedViewModel::class.java)
}
}
}

Does Kotlin have a way to delegate the implementation of an interface to another class?

I am using one activity and three fragments for my application
Each fragment has an interface that is used to communicate with the logic
the activity implements this interface and calls the logic object (a persistent fragment) with the same arguments, so it looks something like this:
class Child : Fragment() {
private fun userInteraction() {
(activity as? ChildInteraction)?.askStuff()
}
interface ChildInteraction {
fun askStuff():Unit
}
}
class ParentActivity : AppCompatActivity(), ChildInteraction {
override fun askStuff() {
(supportFragmentManager.findFragmentByTag("LOGIC") as? ChildInteraction).askStuff()
}
}
class LogicFragment : Fragment(), ChildInteraction {
override fun askStuff() {
//do some work here
}
}
the thing is, that each interaction has 5-10 methods in it, and all ParentActivity does is pass on the message, is there a way to simplify the passing along?
I know you can't do this in Java but I was hoping there is a way for Kotlin to do it

Take a look on setTargetFragment and getTargetFragment. Here is an example of Fragment-to-Fragment communication:
interface ChildInteraction {
companion object
fun askStuff()
}
fun ChildInteraction.Companion.wrap(f: Fragment) = (f.targetFragment as? ChildInteraction)
class Child1 : Fragment() {
private fun userInteraction() {
ChildInteraction.wrap(this)?.askStuff()
}
}
class Child2 : Fragment() {
private fun userInteraction() {
ChildInteraction.wrap(this)?.askStuff()
}
}
class LogicFragment : Fragment(), ChildInteraction {
override fun askStuff() {
//do some work here
}
}
class ParentActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val logic ...
val child1 ...
child1.setTargetFragment(logic, 0)
val child2 ...
child2.setTargetFragment(logic, 0)
}
}

Now I know that this is probably what works for me, so I'll be still accepting the other answer, and because it taught me something I didn't know.
But after some work the way that I handled it was this:
The fragment that attaches looks like this:
class Child : Fragment() {
private var parent: ChildInteraction? = null
override fun onAttach(context: Context?) {
super.onAttach(context)
//this should throw an exception if it is not implemented correctly
parent = (context as LogicProvider).logic!! as Child.ChildInteraction
}
private fun userInteraction() {
parent!!.askStuff()
}
interface ChildInteraction {
fun askStuff():Unit
}
}
Then I have the LogicProvider interface like this:
interface LogicProvider {
val logic: Any?
}
and then the parent will implement logic providers that will pass on the arguments
class ParentActivity : AppCompatActivity(), LogicProvider {
override var logic: Logic? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
var frag: Fragment? = supportFragmentManager.findFragmentByTag("parent_logic")
if (frag == null) {
frag = Logic()
supportFragmentManager.beginTransaction().add(frag, "parent_logic").commitNow()
}
logic = frag as Logic
}
override fun onPause() {
super.onPause()
if (isFinishing)
supportFragmentManager.beginTransaction().remove(supportFragmentManager.findFragmentByTag("parent_logic")).commitNow()
}
}
that way the logic fragment is the only one that has to implement interfaces
class Logic : Fragment(), Child.ChildInteraction, Child2.ChildInteraction2 {
override fun askStuff() {
//do stuff here
}
override fun askStuff2() {
//do other stuff here
}
}