None of the other instances of this question are solving my problem. I have a Fragment that appears at the end of a transaction sequence. It is meant to close the app when a Timer contained within it completes:
var terminalTimer: Timer? = null
class TerminalFragment : Fragment() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_terminal, container, false)
}
override fun onStart() {
super.onStart()
initUi()
startCountDown()
}
override fun onStop() {
super.onStop()
AppLog.i(TAG, "onStop()")
stopCountDown()
}
private fun startCountDown() {
if (terminalTimer == null) {
terminalTimer = Timer()
terminalTimer!!.schedule(object : TimerTask() {
override fun run() {
AppLog.i(TAG, "Terminal countdown finished")
{
activity?.finish()
}
}, 5000)
}
}
private fun stopCountDown() {
AppLog.i(TAG, "stopCountDown()")
terminalTimer?.cancel()
terminalTimer?.purge()
terminalTimer = null
}
private fun returnToStart() {
AppLog.i(TAG, "returnToStart()")
(context as MainActivity).restartFlow() // calls popBackStackImmediate() for every fragment in the backstack, returning user to the beginning of their flow
}
companion object {
#JvmStatic
fun newInstance(terminalType: String, amountLoaded: Double) =
TerminalFragment().apply {
arguments = Bundle().apply {
}
}
}
}
stopCountDown() is being called whenever the fragment is navigated away from, but it somehow survives sometimes and closes the app from another Fragment. Using logs, I've also discovered that there appears to be 2 instances of this timer sometimes. How do I insure that this countdown is never active outside of this fragment and is cancelled/ destroyed in the Fragment's onStop()?
Related
I am using StateFlow in my app and in my Fragment I use this to -
private var job: Job? = null
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
job = lifecycleScope.launchWhenResumed {
viewModel.getData().collect {
// ...
}
}
}
override fun onPause() {
job?.cancel()
super.onPause()
}
As you see I cancel the job in onPause. How could I use a generalized function so that I can avoid doing the job?.cancel in every fragment.
I prefer not to use a BaseFragment
A simple solution would be to utilize the fragments lifecycle to automatically cancel the job when it is paused.
fun CoroutineScope.launchUntilPaused(lifecycleOwner: LifecycleOwner, block: suspend CoroutineScope.() -> Unit){
val job = launch(block = block)
lifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver {
override fun onPause(owner: LifecycleOwner) {
job.cancel()
lifecycleOwner.lifecycle.removeObserver(this)
}
})
}
//Usage
class MyFragment: Fragment() {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
lifecycleScope.launchUntilPaused(this){
someFlow.collect{
...
}
}
}
}
If you have many of these jobs per fragment, I would advice to use a custom CoroutineScope instead, to avoid having many lifecycle observers active.
class CancelOnPauseScope(lifecycleOwner: LifecycleOwner): CoroutineScope by MainScope(){
init{
lifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver{
override fun onPause(owner: LifecycleOwner) {
cancel()
lifecycleOwner.lifecycle.removeObserver(this)
}
})
}
}
class MyFragment: Fragment() {
private val scope = CancelOnPauseScope(this)
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
scope.launch{
someFlow.collect{
...
}
}
}
}
a new way:
// Start a coroutine in the lifecycle scope
lifecycleScope.launch {
// repeatOnLifecycle launches the block in a new coroutine every time the
// lifecycle is in the STARTED state (or above) and cancels it when it's STOPPED.
repeatOnLifecycle(Lifecycle.State.STARTED) {
}
}
public class AnyOfYourFragments extends AbsractFragment{
//you do here what you want to do
}
And in your AbstractFragment:
public abstract class AbstractFragment extends Fragment{
private var job: Job? = null
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
job = lifecycleScope.launchWhenResumed {
viewModel.getData().collect {
// ...
}
}
}
override fun onPause() {
job?.cancel()
super.onPause()
}
}
I don't know kotlin, so my code is kind of mix with java but i'm sure you got the idea
MyActivity is...
private var preso: ClientResultPresentationFragment? = null
private var presoHelper: PresentationHelper? = null
private val presoListener = object: PresentationHelper.Listener{
override fun initSecondDisplay(display: Display?) {
Log.d("preso", "initSecondDisplay()")
preso = MytPresentationFragment.newInstance(this#MyActivity, display)
preso!!.show(fragmentManager, PRESO) // PRESO is a static value.
}
override fun clearPreso(switchToInline: Boolean) {
if (preso != null) {
preso!!.dismiss()
preso = null
}
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_my)
// Must open second display at the same time.
onCreatePreso()
refinedResultData = intent.extras!!.getParcelable(RESULT_DATA)
Log.d("result", "${resultData.toString()}")
init(resultData!!)
}
private fun init(data: ResultData){
initView(data)
preso!!.syncData(data)
}
private initView(data: ResultData){
// TODO: initViews...
}
private fun onCreatePreso(){
presoHelper = PresentationHelper(this, presoListener)
presoHelper!!.enable()
}
override fun onResume() {
super.onResume()
presoHelper?.onResume()
}
override fun onPause() {
presoHelper?.onPause()
super.onPause()
}
My Presentation Fragment is...
var mView: View? = null
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
Log.d("preso", "onCreateView()")
mView = LayoutInflater.from(context).inflate(R.layout.fragment_my, container, false)
return mView
}
fun syncData(data: ResultData){
Log.d("preso", "syncData()->${data.toString()}")
initView()
// return >>> here...
mView!!.tv_title.text = "${data.title}" // <<< crash here >>>
// TODO: set initial data
}
fun initView(){
// initViews...
}
companion object {
fun newInstance(context: Context?, display: Display?): MyPresentationFragment {
val frag = MyPresentationFragment()
frag.setDisplay(context, display)
return frag
}
}
And the log is...
"resultData.toString()"
initSecondDisplay()
"syncData()->${data.toString()}"
crash------------------
if I just uncomment return part in syncData() of Presentation Fragment(It will not access the views)
"resultData.toString()"
initSecondDisplay()
"syncData()->${data.toString()}"
onCreateView()
So, syncData() is called earlier than onCreateView(). What should I do? I moved preso!!.syncData() after preso!!.show(fragmentManager, PRESO) and it's the same.
Since FragmentManager operations is async, you should send a callback from your fragment to the activity in the fragment OnViewCreated or maybe OnResume and only then send the data from the activity to the fragment.
Or you can just use ViewModel and LiveData to provide your data to fragments
I have a TimerService that I'd like to bind to with a TimerFragment, so I can call the Service's methods and observe its LiveData in the fragment. The problem I'm running into is that when I start my fragment, it's telling me that the lateinit var timerService hasn't been initialized by the time I try to use it in onStart. I thought I was starting the service and binding to it by that time in the fragment lifecycle, so I'm not sure what's causing the issue.
My fragment code is as follows:
class TimerFragment : Fragment() {
private lateinit var scaleUp: ObjectAnimator
private lateinit var alphaDown: ObjectAnimator
private lateinit var timerService: TimerService
private var bound = false
private val connection = object : ServiceConnection {
override fun onServiceConnected(name: ComponentName?, service: IBinder?) {
val binder = service as TimerService.LocalBinder
timerService = binder.getService()
bound = true
}
override fun onServiceDisconnected(name: ComponentName?) {
bound = false
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setHasOptionsMenu(true)
requireActivity().startService(Intent(requireContext(), TimerService::class.java))
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_timer, container, false)
}
override fun onStart() {
super.onStart()
Intent(requireContext(), TimerService::class.java).also{ intent ->
requireActivity().bindService(intent, connection, Context.BIND_AUTO_CREATE)
}
timerService.secondsElapsed.observe(viewLifecycleOwner, Observer {
updateTimerUI(it)
})
timerService.timerState.observe(viewLifecycleOwner, Observer {
updateButtons(it)
})
}
override fun onStop() {
super.onStop()
requireActivity().unbindService(connection)
bound = false
}
// other stuff
}
i have an issue with an app that use ViewPager for display fragment. All works fine until the app goes in background and be killed from OS. It seems that after restore i have 2 IncidentScreenFragment that handle events, one with a null presenter (MVP) that crash my app.
My HomeActivity looks like:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
presenter.onViewCreated()
initViews(savedInstanceState)
}
private fun initViews(savedInstanceState: Bundle?){
mapView.onCreate(savedInstanceState)
mapView.getMapAsync(this)
initFragment()
initMenu()
}
private fun initFragment(){
homeFragment = HomeScreenFragment.newInstance()
incidentFragment = IncidentScreenFragment.newInstance()
chatFragment = ChatFragment.newInstance()
weatherFragment = WeatherFragment.newInstance()
viewPager.adapter = ViewPagerAdapter(supportFragmentManager, this)
viewPager.offscreenPageLimit = 4
viewPager?.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
override fun onPageScrollStateChanged(state: Int) {}
override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}
override fun onPageSelected(position: Int) {bottom_navigation.currentItem = position}
})
}
override fun getFragmentByPos(pos: Int): Fragment {
return when(pos){
0 -> homeFragment
1 -> incidentFragment
2 -> chatFragment
3 -> weatherFragment
else -> {
homeFragment
}
}
}
And my Adapter:
class ViewPagerAdapter internal constructor(fm: FragmentManager, activity:infinite_software.intelligence_center.intelligencecenter.ui.home.FragmentManager) : FragmentPagerAdapter(fm) {
private val COUNT = 4
private val activity = activity
override fun getItem(position: Int): Fragment{
var fragment: Fragment? = null
when (position) {
0 -> fragment = activity.getFragmentByPos(0)
1 -> fragment = activity.getFragmentByPos(1)
2 -> fragment = activity.getFragmentByPos(2)
3 -> fragment = activity.getFragmentByPos(3)
}
return fragment!!
}
override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
super.destroyItem(container, position, `object`)
}
override fun getCount(): Int {
return COUNT
}
override fun getPageTitle(position: Int): CharSequence? {
return "Section " + (position + 1)
}
}
Each Fragment have a static method that return new Fragment:
companion object {
fun newInstance(): HomeScreenFragment {
return HomeScreenFragment()
}
}
When the app has been killed in background i figure out that there is 2 objects (Fragment) that listen to event, one with Presenter correctly instantiate and one without.
Below my abstract BaseFragment class:
abstract class BaseFragment<P : BasePresenter<BaseView>> : BaseView,Fragment() {
protected lateinit var presenter: P
override fun getContext(): Context {
return activity as Context
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
return super.onCreateView(inflater, container, savedInstanceState)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
presenter = instantiatePresenter()
}
override fun showError(error: String) {
(activity as BaseActivity<BasePresenter<BaseView>>).showError(error)
}
override fun showError(errorResId: Int) {
(activity as BaseActivity<BasePresenter<BaseView>>).showError(errorResId)
}
abstract fun onBackPressed(): Boolean
/**
* Instantiates the presenter the Fragment is based on.
*/
protected abstract fun instantiatePresenter(): P
abstract val TAG: String
Incident Fragment code:
class IncidentScreenFragment: BaseFragment<IncidentScreenPresenter>(), BaseView, IncidentView, AlertFilterListener, AlertItemClickListener, IncidentDetailListener {
var rvAdapter : IncidentAdapter? = null
var state : Int = LIST_STATE
override fun instantiatePresenter(): IncidentScreenPresenter {
return IncidentScreenPresenter(this)
}
override val TAG: String
get() = "INCIDENT"
override fun getContext(): Context {
return activity as Context
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
super.onCreateView(inflater, container, savedInstanceState)
return inflater.inflate(R.layout.fragment_incident, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
initViews()
presenter.onViewCreated()
initObserve()
}
private fun initViews(){
//Reclycler view
alertRV.layoutManager = LinearLayoutManager(context)
rvAdapter = IncidentAdapter(ArrayList(), context, this)
alertRV.adapter = rvAdapter
//Apply Listeners
headerBox.setFilterListener(this)
incidentDetailView.setListener(this)
}
override fun initObserve() {
//Init observe presenter model
val alertObserver = Observer<ArrayList<AlertModel>> { alerts ->
Timber.d("Data received from Presenter [$alerts]")
showAlertList(alerts)
}
presenter.filteredAlertList.observe(context as BaseActivity<BasePresenter<BaseView>>,alertObserver)
}
override fun updateThisFilters(boxState: Boolean, level: Int) {
presenter.updateFilterList(boxState,level)
}
fun showOnlyThisLevel(level:Int){
presenter.showOnlyThisLevel(level)
headerBox.disableBoxExcept(level)
}
fun showAlertList(list: ArrayList<AlertModel>){
rvAdapter?.updateData(list)
}
override fun onItemClick(model: AlertModel) {
presenter.loadAlertDetail(model)
}
override fun showAlertDetail(model: AlertModel) {
incidentDetailView.setUpFromModel(model)
WhiteWizard.slideLeftEffect(incidentDetailView,incidentListRootElement)
state = DETAIL_STATE
}
override fun onbackFromDetailPressed() {
WhiteWizard.slideRightEffect(incidentListRootElement,incidentDetailView)
state = LIST_STATE
}
override fun showLoader() {
loaderIncident.visibility = View.VISIBLE
}
override fun hideLoader() {
loaderIncident.visibility = View.INVISIBLE
}
override fun onBackPressed(): Boolean {
when(state){
LIST_STATE -> return false
DETAIL_STATE -> {
onbackFromDetailPressed()
return true
}
else -> return false
}
}
fun newInstance(): IncidentScreenFragment {
return IncidentScreenFragment()
}
}
When i click on the button in homePage to display fragment content i got:
Process: XXXXXX, PID: 3192
kotlin.UninitializedPropertyAccessException: lateinit property presenter has not been initialized
at infinite_software.intelligence_center.intelligencecenter.base.BaseFragment.getPresenter(BaseFragment.kt:11)
at XXXXXX.ui.home.incidentScreen.IncidentScreenFragment.showOnlyThisLevel(IncidentScreenFragment.kt:78)
at XXXXXX.ui.home.HomeActivity.filterDataWithSeverity(HomeActivity.kt:110)
at XXXXXX.ui.home.homeScreen.HomeScreenFragment.filterBy(HomeScreenFragment.kt:76)
at XXXXXX.ui.home.homeScreen.HomeScreenFragment$initViews$5.onClick(HomeScreenFragment.kt:56)
If i try to print the id of Fragment, i obtain 2 different ids from method call showOnlyThisLevel() and onBackPressed(). What i miss ?
After doing some research, it seems that the problem stems from the misnaming of FragmentPagerAdapter's method - being named getItem(), but not clearly specifying that the abstract method getItem(int position) is supposed to return a new instance of a fragment rather than just "get an instance of one".
Of course, there is not much we can do about an incorrect name after it's been out in the wild for 7 years, but at least we can fix the bug that stems from this issue in your code ;)
Without further ado, the cause of your NPE is that onCreateView (where your Presenter is instantiated) is never called.
This happens because you are creating the fragment here:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
...
homeFragment = HomeScreenFragment.newInstance()
incidentFragment = IncidentScreenFragment.newInstance()
}
You return this fragment from inside getItem(int position) in your FragmentPagerAdapter:
override fun getItem(position: Int): Fragment = when(position) {
...
1 -> activity.incidentFragment
...
}
So what we know about activity.incidentFragment is that in it, onCreateView() is never called.
This is caused by the fact that it's never actually added to a FragmentManager and never displayed on the screen.
That's because super.onCreate(savedInstanceState) in Activity recreates all Fragments, using their no-args constructor, via reflection, while keeping their tag (see findFragmentByTag).
So as you can see in this answer, or as I can quote here:
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
makeFragmentName(container.getId(), itemId));
The getItem(position) method is only called if the Fragment is not found by the fragment tag that the FragmentPagerAdapter sets for the fragment, which IS automatically recreated after low memory condition kills your app.
Therefore, YOUR new fragment (that you create by hand in the Activity) is NEVER used, and therefore it has no view, never initialized, never added to FragmentManager, it's not the same instance as what's actually inside your ViewPager, and it crashes when you call it. Boom!
Solution is to instantiate the Fragment inside FragmentPagerAdapter's getItem(position) method. To get an instance of the fragment, use this answer.
I am using Kotlin Android Extension to access view directly by their id.
I have a progress bar which I access directly in fragment using id i.e progress_bar
<ProgressBar
android:id="#+id/progress_bar"
style="#style/Widget.AppCompat.ProgressBar.Horizontal"
android:layout_width="match_parent"
android:layout_height="15dp"
android:indeterminate="true"/>
In fragment, I am showing and hiding it with this code
progress_bar.visibility = if (visible) View.VISIBLE else View.GONE
It is working perfectly until I rotate the screen. After that, it throws the exception
java.lang.IllegalStateException: progress_bar must not be null.
The variable gets null on screen rotation. How to solve this problem?
Fragment code
class SingleAppFragment : Fragment() {
private lateinit var appName: String
companion object {
fun newInstance(appName: String = ""): SingleAppFragment {
val fragment = SingleAppFragment()
val args = Bundle()
args.putString(Constants.EXTRA_APP_NAME, appName)
fragment.arguments = args
return fragment
}
}
private var mListener: OnFragmentInteractionListener? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
appName = if (arguments != null && !arguments.getString(Constants.EXTRA_APP_NAME).isEmpty()) {
arguments.getString(Constants.EXTRA_APP_NAME)
} else {
Constants.APP_NAME_FACEBOOK
}
}
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
return inflater!!.inflate(R.layout.fragment_single_app, container, false)
}
override fun onViewCreated(view: View?, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
initView()
setEventListeners()
}
private fun initView() {
var canShowSnackBar = true
web_single_app.webViewClient = object : WebViewClient() {
override fun onPageStarted(view: WebView?, url: String?, favicon: Bitmap?) {
super.onPageStarted(view, url, favicon)
showHideProgressBar(true)
canShowSnackBar = true
}
override fun onPageFinished(view: WebView?, url: String?) {
super.onPageFinished(view, url)
showHideProgressBar(false)
}
override fun onReceivedError(view: WebView?, request: WebResourceRequest?, error: WebResourceError?) {
web_single_app.stopLoading()
if (canShowSnackBar) {
mListener?.onErrorWebView()
canShowSnackBar = false
}
}
}
web_single_app.settings.javaScriptEnabled = true
web_single_app.loadUrl(Constants.APP_NAME_URL_MAP[appName])
}
private fun setEventListeners() {
back_web_control.setOnClickListener({
web_single_app.goBack()
})
}
fun showHideProgressBar(visible: Boolean) {
progress_bar_web_control.visibility = if (visible) View.VISIBLE else View.GONE
}
fun loadUrl(appName: String) {
web_single_app.loadUrl(Constants.APP_NAME_URL_MAP[appName])
}
override fun onAttach(context: Context?) {
super.onAttach(context)
if (context is OnFragmentInteractionListener) {
mListener = context
}
}
override fun onDetach() {
super.onDetach()
mListener = null
}
interface OnFragmentInteractionListener {
fun onErrorWebView()
}
}
Steps to reproduce:
Start Activity
Fragment get loaded
At Fragment load, I load an URL and show a progress bar
At loading the URL I rotate the phone and the progress bar variable gets null
In my case this bug happens from time to time. Of course, onViewCreated() is a good method to place your code in. But sometimes it's strangely not enough. And setRetainInstance(true) may help, may not. So sometimes this helps: access your Views with a view variable. You can even access them inside onCreateView(). You can use ?. for a guarantee that an application won't crash (of course, some views won't update in this case). If you wish to get context, use view.context.
In my case this bug reproduced only in Kotlin coroutines.
private fun showProgress(view: View) {
view.progressBar?.visibility = View.VISIBLE
}
private fun hideProgress(view: View) {
view.progressBar?.visibility = View.GONE
}
Then in code:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
showData(view)
}
private fun showData(view: View) {
showProgress(view)
adapter = SomeAdapter()
adapter.setItems(items)
val divider = SomeItemDecoration(view.context)
view.recycler_view?.run {
addItemDecoration(divider)
adapter = this#SomeFragment.adapter
layoutManager = LinearLayoutManager(view.context)
setHasFixedSize(true)
}
hideProgress(view)
}
In which method do you get the progress_bar by Id?
Please consider the fragment state lifecycle. Maybe you try to load it when the view is not ready yet.
Ensure your progress_bar variable is assigned only after the view is ready. For example in the
onViewCreated method.
See here the official Android lifecycle:
Update
As #CoolMind pointed out the diagram doesn't show the method onViewCreated.
The complete Android Activity/Fragment lifecycle can be found here:
Add retain intance true to the fragment so that it will not be destroyed when an orientation changes occurs
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
retainInstance=true
}
Also do a null check using safe call operator before accessing views
fun showHideProgressBar(visible: Boolean) {
progress_bar_web_control?.visibility = if (visible) View.VISIBLE else View.GONE
}