I have tried to simplify my problem as much as possible, I hope it is clear what I am asking.
I would like to obtain in the fragment the value of the variable pto1 after modifying it through the onClickEvent function of class B.
I understood that doing so is not possible because when I have
val classA = A ()
in the fragment,a new instance of class A is recreated and a new pto1 it is recreated and set to 0.0 .
how can i access pto1 from fragment after modifying it with class B?
class A {
var pto1 = 0.0
fun changeValue(a: Double){
pto1 = a
}
}
--------------------------------
class B {
val classA = A()
fun onClickEvent(b:Double){
classA.changeValue(b)
}
}
--------------------------------
fragment D {
val classA = A()
onCreateView( ... ){
val botton = view.findViewById<Button>(R.id.button)
button.setOnClickListner{
val f = classA.pto1
}
}
}
There is a couple of options here
Make it static
class A {
companion object {
var pto1 = 0.0
}
}
Is this a View Model problem?
Use the navgraph viewmodel or a viewmodel from the activity.
Make it persistent: you can use the SharedPreferences or ROOM to save it.
Make the host of both fragments have it and then fragments can acces it. If the host is the activity:
class MyActivity {
val a = A()
fun getA() = a
}
(requireActivity() as? MyActivity).?getA()
Is this a navigation result?
Take a look here How to get a result from fragment using Navigation Architecture Component?
Related
I use Koin and Fragment + ViewModel per screen.
In my HomeFragment I have list with post.
When user selects post I navigate user to PosDetailsFragment and I want to display info about post.
class HomeFragment : Fragment() {
private val homeViewModel by viewModel<HomeViewModel>()
//when user select post I set that value to LeadViewModel (I want to make that viewModel as common for some fragment)
leadViewModel.state.selectedPost.value = action.post
}
class PostDetailsFragment : Fragment() {
private val leadViewModel by sharedViewModel<LeadViewModel>()
//always null
val post = leadViewModel.state.selectedPost.value
}
My Koin module:
viewModel { LeadViewModel() }
viewModel { HomeViewModel(get(bottomNavigationCommander), get()) }
viewModel { AddPostViewModel() }
What is wrong? It looks like instance of LeadViewModel in PostDetailsFragment is completely different than in HomeFragment?
Try making the val as backing field
val post
get() = leadViewModel.state.selectedPost.value
Probably it has a simple solution that I cant see. I have a fragment with a ViewModel, The Viewmodel has a method inside of it that I want to call from my fragment and supply the arguments for. but when I try to call the method it shows an error "Unsolved Reference"
class DetailFragmentViewModel : ViewModel() {
private val repo = Crepository.get()
private val itemIdlivedata = MutableLiveData<UUID>()
var crimeLiveDate: LiveData<Crime?> = Transformations.switchMap(itemIdlivedata){ it ->
repo.getitem(it) }
fun LoadItem(itemuuid:UUID){
itemIdlivedata.value = itemuuid
}
}
Fragment Class:
private val crimeDetailVM : ViewModel by lazy {
ViewModelProvider(this).get(DetailFragmentViewModel::class.java)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
...
crimeDetailVM.LoadItem <- Unsolved Reference
}
Thanks for the help!
EDIT:IT HAS A SIMPLE SOLUTION, I DID NOT CAST THE VIEW MODEL TO THE VIEW MODEL CLASS,THANKS FOR THE HELP EVERYONE
You are doing downcasting DetailFragmentViewModel to ViewModel. That is why you are not accessing to DetailFragmentViewModel methods.
Use
private val crimeDetailVM : DetailFragmentViewModel by lazy {
ViewModelProvider(this).get(DetailFragmentViewModel::class.java)
}
Instead of
private val crimeDetailVM : ViewModel by lazy {
ViewModelProvider(this).get(DetailFragmentViewModel::class.java)
}
Also this way is not idiomatic i suggest you to use kotlin extension
val viewModel by viewModels<DetailFragmentViewModel>()
But before do that you need to add the dependency which is Fragment KTX to your app gradle file.
https://developer.android.com/kotlin/ktx
You need activity context
try:
ViewModelProvider(requireActivity()).get(DetailFragmentViewModel::class.java)
you can use also extend view model by ActivityViewModel
eg.-> class DetailFragmentViewModel(application:Application) : AndroidViewModel(applivation){}
This video (MVVM & Nested Fragments/Views: ViewModel Contracts - By Marcos Paulo Damesceno, Bret Erickson
droidcon San Francisco 2019
) shows a way to deal with communication between activities/fragments using ViewModel.
I am implementing it for learning purpose but I got stuck.
// 18:35 of the video
private const val VM_KEY = "view_model_contract_key"
fun <T> Fragment.viewModelContracts() = lazy {
val clazz: Class<ViewModel> = arguments?.getSerializable(VM_KEY) as Class<ViewModel>
val viewModelProvider = ViewModelProvider(requireActivity())
return#lazy viewModelProvider.get(clazz) as T
}
The ViewModelStoreOwner passed as parameter is an Activity, but if I have a Fragment inside another Fragment where both of them share the same ViewModel, the ViewModel returned by viewModelContracts() will be a different object as the one created by the Parent Fragment.
interface ChildViewModelContract {
// ...
}
class SomeViewModel : ViewModel(), ChildViewModelContract {
// ...
}
class ParentFragment: Fragment {
private val viewModel: SomeViewModel by viewModels()
// ...
}
class ChildFragment: Fragment {
private val viewModelContract: ChildViewModelContract by viewModelContracts()
// ...
}
The ideal solution would be to check in fun <T> Fragment.viewModelContracts() if the ViewModelProvider of the parent fragment has the ViewModel stored in it, and if not, use the ViewModelProvider of the Activity. But I'm not knowing how to do this.
fun <T> Fragment.viewModelContracts() = lazy {
val clazz: Class<ViewModel> = arguments?.getSerializable(VM_KEY) as Class<ViewModel>
val parentFragment = parentFragment
if (parentFragment != null) {
val viewModelProvider = ViewModelProvider(parentFragment)
// is there any way to do something like this?
if (viewModelProvider.isViewModelStored(clazz)) {
return#lazy viewModelProvider.get(clazz) as T
}
}
val viewModelProvider = ViewModelProvider(requireActivity())
return#lazy viewModelProvider.get(clazz) as T
}
I've tried extracting the value into a base class and having the ViewModels extend it. When I do that, however, the Observer isn't sticking to the LiveData. For instance, when I have a parent class with LiveData:
class Base : ViewModel() {
private val _ data = MutableLiveData()
val data: LiveData = _data
fun someEvent(foo: Foo) { // update _data }
}
class Derived : Base()
class Derived1 : Base()
Then get one of those ViewModels and observe data:
class Frag : Fragment {
onViewCreated() {
// get Derived, ViewModelProviders.of ...etc
derived.data.observe { // Doesn't observe changes }
}
}
Calling Base.someEvent(foo) doesn't notify the LiveData in the Fragment.
I want to avoid getting a reference to both subclasses and invoking someEvent on each. One thing to note is that I'm using a single Activity approach and all ViewModels are Activity scoped.
class Derived : Base()
and
class Derived1 : Base()
have their own instance of:
private val _ data = MutableLiveData()
val data: LiveData = _data
that means you need to
derived.data.observe { // do something }
derived1.data.observer { // do something }
derived.someEvent(someFoo)
derived1.someEvent(someFoo)
You are trying to achieve something in a wrong way.
I need to open one activity from several different points in the app. Let's say from Settings fragment, Main Activity and Navigation drawer (fragment). I don't want to copy/paste the same method and the method is very specific, it should be exactly the same (because it registeres Firebase events). How to structure the code in effective way? Where to put this method? One idea is to have a global ActivityUtils.kt file with just methods and it would be used to store these methods. I'm interested in the alternatives and what are pros and cons of each.
I would create a companion object in the Activity you need to open:
class YourActivity : AppCompatActivity() {
companion object {
fun start(ctx: Context) {
// put your logic here (registering of Firebase events)
val i = Intent(ctx, YourActivity::class.java)
ctx.startActivity(i)
}
}
}
And call it from another activity:
YourActivity.start(this)
or from another fragment:
YourActivity.start(context)
Use an extension method:
fun Activity.doMyStuff() {}
That can be called from any class extending Activity:
doMyStuff()
Extension functions like this shouldn't go inside a class, but rather inside a file. So if you were to make an ActivityUtils.kt file, don't have any sort of class ActivityUtils {} stuff in it. The function(s) should just go directly into the file.
Why not to use MVP?
Like,
interface IView {
val context: Context
}
interface IPresenter {
fun launchActivity(view: IView)
}
class MyActivityModel
{
var key = "key"
/*some other data*/
fun getParcelableObject(): Parcelable
{
return /*some parcelable from model data*/
}
}
class MyActivity : AppCompatActivity(), IView
{
override val context: Context
get() = this
}
class MyActivityPresenter() : IPresenter
{
private var model: MyActivityModel = MyActivityModel()
override fun launchActivity(view: IView)
{
val intent = Intent(view.context, MyActivity::class.java)
intent.putExtra(model.key, model.getParcelableObject())
view.context.startActivity(intent)
}
fun setSomeDataToModel(someData: Any) {
}
}
/*Everyone who wants to use presenter, must be a Context and implement IView*/
fun use()//in some fragment, or activity implementing IView
{
MyActivityPresenter().launchActivity(this)
//or
val presenter = MyActivityPresenter()
presenter.setSomeDataToModel("some data")
presenter.launchActivity(this)
}