Develop Reference

When flow collect stop itself?

There is ParentFragment that shows DialogFragment. I collect a dialog result through SharedFlow. When result received, dialog dismissed. Should I stop collect by additional code? What happens when dialog closed, but fragment still resumed?
// ParentFragment
private fun save() {
val dialog = ContinueDialogFragment(R.string.dialog_is_save_task)
dialog.show(parentFragmentManager, "is_save_dialog")
lifecycleScope.launch {
dialog.resultSharedFlow.collect {
when (it) {
ContinueDialogFragment.RESULT_YES -> {
viewModel.saveTask()
closeFragment()
}
ContinueDialogFragment.RESULT_NO -> {
closeFragment()
}
ContinueDialogFragment.RESULT_CONTINUE -> {
// dont close fragment
}
}
}
}
}
class ContinueDialogFragment(
#StringRes private val titleStringId: Int,
#StringRes private val messageStringId: Int? = null
) : DialogFragment() {
private val _resultSharedFlow = MutableSharedFlow<Int>(1)
val resultSharedFlow = _resultSharedFlow.asSharedFlow()
override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
return activity?.let { context ->
AlertDialog.Builder(context)
.setTitle(getString(titleStringId))
.setMessage(messageStringId?.let { getString(it) })
.setPositiveButton(getString(R.string.dialog_yes)) { _, _ ->
_resultSharedFlow.tryEmit(RESULT_YES)
}
.setNegativeButton(getString(R.string.dialog_no)) { _, _ ->
_resultSharedFlow.tryEmit(RESULT_NO)
}
.setNeutralButton(getString(R.string.dialog_continue)) { _, _ ->
_resultSharedFlow.tryEmit(RESULT_CONTINUE)
}
.create()
} ?: throw IllegalStateException("Activity cannot be null")
}
companion object {
const val RESULT_YES = 1
const val RESULT_NO = 0
const val RESULT_CONTINUE = 2
}
}

When a Flow completes depends on its original source. A Flow built with flowOf or asFlow() ends once it reaches the last item in its list. A Flow built with the flow builder could be finite or infinite, depending on whether it has an infinite loop in it.
A flow created with MutableSharedFlow is always infinite. It stays open until the coroutine collecting it is cancelled. Therefore, you are leaking the dialog fragment with your current code because you are hanging onto its MutableSharedFlow reference, which is capturing the dialog fragment reference. You need to manually cancel your coroutine or collection.
Or more simply, you could use first() instead of collect { }.
Side note, this is a highly unusual uses of a Flow, which is why you're running into this fragile condition in the first place. A Flow is for a series of emitted objects, not for a single object.
It is also very fragile that you're collecting this flow is a function called save(), but you don't appear to be doing anything in save() to store the instance state such that if the activity/fragment is recreated you'll start collecting from the flow again. So, if the screen rotates, the dialog will reappear, the user could click the positive button, and nothing will be saved. It will silently fail.
DialogFragments are pretty clumsy to work with in my opinion. Anyway, I would take the easiest route and directly put your behaviors in the DialogFragment code instead of trying to react to the result back in your parent fragment. But if you don't want to do that, you need to go through the pain of calling back through to the parent fragment. Alternatively, you could use a shared ViewModel between these two fragments that will handle the dialog results.

I believe you will have a memory leak of DialogFragment: ParentFragment will be referencing the field dialog.resultSharedFlow until the corresponding coroutine finishes execution. The latter may never happen while ParentFragment is open because dialog.resultSharedFlow is an infinite Flow. You can call cancel() to finish the coroutine execution and make dialog eligible for garbage collection:
lifecycleScope.launch {
dialog.resultSharedFlow.collect {
when (it) {
ContinueDialogFragment.RESULT_YES -> {
viewModel.saveTask()
closeFragment()
cancel()
}
ContinueDialogFragment.RESULT_NO -> {
closeFragment()
cancel()
}
ContinueDialogFragment.RESULT_CONTINUE -> {
// dont close fragment
}
}
}
}

registerForActivityResult() outside onCreate() with Compose

So I am trying to launch the intent Intent.ACTION_OPEN_DOCUMENT. I first tried with startActivityForResult but I noticed it was depreciated so I tried to find another way to do this. So I found the registerForActivityResult method but it turns out it must run after onCreate() has finished :
Note: While it is safe to call registerForActivityResult() before your fragment or activity is created, you cannot launch the ActivityResultLauncher until the fragment or activity's Lifecycle has reached CREATED.
Since I am using Jetpack Compose and setContent is in onCreate() my Activity has actually never finished creating because all my Composables functions are run in the setContent of my MainActivity
So how can I achieve this ?

Using the latest version of activity-compose you can use rememberLauncherForActivityResult() to register a request to Activity#startActivityForResult.
Something like:
val result = remember { mutableStateOf<Uri?>(null) }
val launcher = rememberLauncherForActivityResult(ActivityResultContracts.OpenDocument()) {
result.value = it
}
Button(onClick = { launcher.launch(arrayOf("application/pdf")) }) {
Text(text = "Open Document")
}
result.value?.let {
//...
}

How to Pass finish() from Activity class as a function parameter (So the code can be reused in Kotlin)?

I have to use this peice of code twice in two different places in two different activites. No good programmer would willingly want to use same code in multiple places without reusing it.
//when back key is pressed
override fun onBackPressed() {
dialog.setContentView(twoBtnDialog.root)
twoBtnDialog.title.text = getString(R.string.warning)
twoBtnDialog.msgDialog.text = getString(R.string.backPressWarning)
twoBtnDialog.ok.text = getString(R.string.exit)
twoBtnDialog.cancel.text = getString(R.string.cancel)
twoBtnDialog.ok.setOnClickListener {
//do nav back
finish()
dialog.dismiss()
}
twoBtnDialog.cancel.setOnClickListener {
dialog.dismiss() //just do nothing
}
dialog.window?.setBackgroundDrawable(ColorDrawable(Color.TRANSPARENT))
dialog.show()
}
I can move it to one place, but the problem is I have to pass in the finish() function from Activity Class to close the calling activity.
My simple question is how can I resue it ? Or How can I pass this function (finish()) to a different class (which is in some other file).

Take a function type parameter in your method.
fun doBackPress(finish: () -> Unit) {
// you need to invoke the finish method when necessary
finish.invoke()
}
Then you need to call the method and have to pass the finish() method from any other activity or fragment method like bellow.
override fun onBackPressed() {
doBackPress { finish() }
}

You could make an interface and extension function, which I think is less messy than trying to pass everything you need as parameters to a function, because it communicates intent better and makes it harder to do something wrong.
interface MyDialogOwner {
val dialog: Dialog
val twoBtnDialog: MyDialogBinding
fun Activity.handleBackPress() {
//the exact same content you have in your function now.
}
}
// In Activity:
override fun onBackPressed() = handleBackPress()
Your Activities should implement the interface, using your existing properties for dialog and twoBtnDialog (just add override in front of their declarations).
I'm assuming twoBtnDialog is a view binding.

Kotlin Flow.collect executes but does not update ui onConfigurationChanged

I'm using Flow to get data from Room then I call Flow.collect in my FragmentLogic class. Inside collect{} I do some work and update the View through an Interface( example: view.updateAdapter(collectData)). This works fine until an onConfigurationChanged is called and the screen rotates, the code inside collect executes and works in Logcat but anything that changes the UI does not work, the function updateAdapter() is called however nothing happens. One solution I found is to call the function beginObservingProductList() again in onStart() if savedinstance is not null but that creates two instances of the collect{} and they both show in logcat.
I want the UI changes to work even after onConfigurationChanged is called.
Room Dao class:
#Query("SELECT * FROM product")
fun observableList(): Flow<List<ProductEntity>>
then in the implementation:
productDao.observableList().map { collection ->
collection.map { entity ->
entity.toProduct
}
}.flowOn(DispatchThread.io())
And finally I collect the data and change the view:
private fun beginObservingProductList() = this.launch {
vModel.liveProductList.map {
mapToSelectionProduct(it)
}.collect {
ui { view.updateAdapter(it) }
if (it.isNotEmpty()) {
filledListState()
} else {
emptyListState()
}
updateCosts()
vModel.firstTime = false
}
}

Flow is not lifecycle aware, you should use LiveData to handle configuration changes.
To use LiveData with Flow,
implement androidx.lifecycle:lifecycle-livedata-ktx:2.2.0, then you can use .asLiveData() extension func.
Repository
fun getList()= productDao.observableList().map { collection ->
collection.map { entity ->
entity.toProduct
}
}.flowOn(DispatchThread.io())
ViewModel
val liveData = repository.getList().asLiveData()
Activity/Fragment
viewModel.liveData.observe(this,Observer{ list->
//do your thing
})

unsaved warning on back pressed in fragment

I want to show dialog when user press back or quit from fragment if there are some data unsaved. I am trying to override onbackpressed but unfortunately I got error lateinit property barcodeList has not been initialized. how to solve it?
here is my script on activity:
override fun onBackPressed() {
val theFragment = supportFragmentManager.fragments
for(i in 0 until theFragment.size)
{
if(theFragment[i].tag == "stocker_fragment")
{
StockerFragment().onBackPressed()
}
}
}
and this is in fragment:
fun onBackPressed() {
var check = false
// this barcodeList variable error.
for(i in 0 until barcodeList.size)
{
if(barcodeList[i].barcode.trim()=="")
{
check = true
break
}
}
if (check)
{
AlertHelper(context).onBackPressedAlert()
}
}
FYI: I have initialized barcodeList on onCreateView and everything is fine. only error in onBackPressed.
And my last question is, how do i know if user quit from fragment without pressing back button?

I think the problem is in your onBackPressed() implementation in the Activity. With the line StockerFragment().onBackPressed() you are creating a new instance of the StockerFragment and calling onBackPressed() on it, rather than calling it on the instance that is actively being used.
You should be able to adjust your Activity onBackPressed() like so:
override fun onBackPressed() {
val theFragment = supportFragmentManager.fragments
for(i in 0 until theFragment.size)
{
if(theFragment[i].tag == "stocker_fragment")
{
(theFragment[i] as StockerFragment).onBackPressed()
}
}
}
You can also make this a bit more kotliny like so:
override fun onBackPressed() {
supportFragmentManager.fragments.forEach { fragment ->
if (fragment is StockerFragment) {
fragment.onBackPressed()
}
}
}
You'll probably also want to figure out a way to decide whether the fragment's onBackPressed has determined that the Activity should stick around or not. Then, if the fragment is happy, you should call super.onBackPressed() in the Activity so that the expected back behavior (leave the Activity) happens.