Develop Reference

BaseFragment with viewbinding

To use viewbinding in an android app I am basically creating base classes for Activity & Fragment to remove boilerplate of everytime writing inflating code.
ACTIVITY:
BaseActivity with viewbinding:
abstract class BaseActivity<VB : ViewBinding> : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = getViewBinding()
}
abstract fun getViewBinding(): VB
}
MainActivity:
class MainActivity : BaseActivity<ActivityMainBinding>() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(binding.root)
//we can directly use binding now and it works fine inside activity
//binding.view.doSomething()
}
override fun getViewBinding(): ActivityMainBinding = ActivityMainBinding.inflate(layoutInflater)
}
FRAGMENTS :
BaseFragment:
abstract class BaseFragment<VB : ViewBinding> : Fragment() {
var binding: VB? = null
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding = getViewBinding(view)
}
abstract fun getViewBinding(view: View): VB
}
DemoFragment:
class DemoFragment : BaseFragment<DemoFragmentBinding>() {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//problem is here
binding.txtData.text="Something"
}
override fun getViewBinding(view: View): DemoFragmentBinding = DemoFragmentBinding.bind(view)
}
demo_fragment.xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ui.fragments.DemoFragment">
<TextView
android:id="#+id/txt_data"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="Hello" />
</FrameLayout>
Problem : Unable to access views using binding inside Demofragment. I don't know why it works with activity and not with fragment.
2nd way that I don't want todo:
implementation 'androidx.fragment:fragment-ktx:1.3.1'
class DemoFragment : Fragment(R.layout.demo_fragment) {
lateinit var binding: DemoFragmentBinding
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding = DemoFragmentBinding.bind(view).apply {
txtData.text = "Hello World"
}
}
}

You need to override onCreateView in BaseFragment and initialize the viewbinding
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
_binding = getViewBinding()
return binding.root
}
Then change this line
override fun getViewBinding(view: View): DemoFragmentBinding = DemoFragmentBinding.bind(view)
with
override fun getViewBinding() = DemoFragmentBinding.inflate(layoutInflater)
BaseFragment:
abstract class BaseFragment<VB : ViewBinding> : Fragment() {
private var _binding: VB? = null
val binding get() = _binding!!
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
_binding = getViewBinding()
return binding.root
}
abstract fun getViewBinding(): VB
}
DemoFragment:
class DemoFragment : BaseFragment<DemoFragmentBinding>() {
override fun getViewBinding() = DemoFragmentBinding.inflate(layoutInflater)
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.apply {
txtData.text = "Something"
}
}
}

Here is another way to implement this factory abstraction with ViewBinding. I am sharing the implementation code below. I am using genrics here. If anyone needs further explanation, I am here for that. Make sure you have enabled viewbinding feature already into the build.gradle file. Then use the following BaseFragment.kt as your fragment abstraction.
BaseFragment:
typealias Inflate<T> = (LayoutInflater, ViewGroup?, Boolean) -> T
abstract class BaseFragment<V: ViewBinding>(
private val inflate: Inflate<V>
) : Fragment() {
private lateinit var _binding: V
val binding get() = _binding
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
_binding = inflate(inflater, container, false)
return binding.root
}
}
N:B: Know more about typealias.
HomeFragment:
// Implement the BaseFragment like below
class HomeFragment : BaseFragment<FragmentHomeBinding>(FragmentHomeBinding::inflate) {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
// usages by calling public variable 'binding' from base class
binding.message.text = "update $value"
}
}

I looked through the documentation, I'm not sure if this breaks what you wanted with the abstract pattern in the BaseFragment, but I tested your code with this change and it worked. Only change was in the DemoFragment:
//Add this for the onCreateView implementation
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
binding = DemoFragmentBinding.inflate(LayoutInflater.from(context), null, false)
val view = binding!!.root
return view
}
Then I tested in onViewCreated:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//problem is here
binding?.txtData?.text="Something"
}
And it worked. The documentation I looked at was this section
I think doing this still allows you to avoid some boilerplate, but the onCreateView override is going to be necessary for every fragment, because of the different viewbinding inflation (e.g. DemoFragmentBinding.inflate etc etc)

Uses https://github.com/hoc081098/ViewBindingDelegate
abstract class BaseFragment<VB : ViewBinding>(#LayoutRes layoutId: Int) : Fragment(layoutId) {
protected abstract val binding: VB
}
import com.hoc081098.viewbindingdelegate.*
class MainFragment: BaseFragment<FragmentMainBinding>(R.layout.fragment_main) {
override val binding by viewBinding()
}

Android BottomSheetDialogFragment blinking

I startActivity from BottomSheetDialogFragment.
But when I finish the Activity, the BottomSheetDialogFragment is blinking.
My case is like this one BottomSheetDialog background blinking
But there is no solution.
Here is my screen shot
The code is simple and basic.
MainActivity.class
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val bottomSheetFragment = BottomSheetFragment()
button.setOnClickListener {
bottomSheetFragment.show(supportFragmentManager, "")
}
}
}
BottomSheetFragment.class
class BottomSheetFragment: BottomSheetDialogFragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
return inflater.inflate(R.layout.fragment_bottom_sheet, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
button.setOnClickListener {
startActivity(Intent(context!!, Test2Activity::class.java))
}
}
}

Your Bottom sheet is not Blinking. its the effect of activity when you get back to MainActivity.
in your MainActivity Please implement overridePendingTransition before onCreate()
overridePendingTransition(0,0) // due to this default effect will remove

Android Navigation Component saveState and restoreState

Guys I need your help.
I use android navigation component and want to save backstack after user press button and restore it after. I found 2 methods
navController.saveState(): Bundle and navController.restoreState(bundle: Bundle).
But i have problem in use it. Seems like saveState work greate (i see bundle, and backstack inside), but i dont understand how to use restoreState, because the documentation says:
Restores all navigation controller state from a bundle. This should be called before any call to setGraph.
https://developer.android.com/reference/kotlin/androidx/navigation/NavController#restorestate
Okay, i did it, seems like backstack restored, but on screen i see first fragment (instead of the one I had when I saved it). What i do wrong?
Code:
FirstFragment
private val TAG = this::class.java.name
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_first, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
btn_forward.setOnClickListener { findNavController().navigate(R.id.action_firstFragment_to_secondFragment) }
btn_back.setOnClickListener { requireActivity().onBackPressed() }
}
}
SecondFragment
class SecondFragment : Fragment() {
private val TAG = this::class.java.name
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_second, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
btn_forward.setOnClickListener { findNavController().navigate(R.id.action_secondFragment_to_thirdFragment) }
btn_back.setOnClickListener { requireActivity().onBackPressed() }
}
}
ThirdFragment
class ThirdFragment : Fragment() {
private val TAG = this::class.java.name
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_third, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
btn_finish.setOnClickListener {
(requireActivity() as MainActivity).saveState() //here save bundle
requireActivity().finishAfterTransition()
}
btn_back.setOnClickListener { requireActivity().onBackPressed() }
}
}
MainActivity
class MainActivity : AppCompatActivity() {
private val TAG = "MySuperActivity"
lateinit var navController: NavController
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
Log.d(TAG, "onCreate($savedInstanceState) called")
initNavController()
}
private fun initNavController() {
val navHostFragment = nav_host_fragment as NavHostFragment
val graphInflater = navHostFragment.navController.navInflater
val graph = graphInflater.inflate(R.navigation.main_graph)
navController = navHostFragment.navController
navHostFragment.childFragmentManager
if (App.instance.savedBundle != null) {
Log.d(TAG, "bundle: ${App.instance.savedBundle}")
navController.restoreState(App.instance.savedBundle)
graph.startDestination = R.id.thirdFragment
}
navController.graph = graph
Log.d(TAG, "navController.currentDestination: ${navController.currentDestination}")
Log.d(TAG, "navController.graph.startDestination: ${navController.graph.startDestination}")
}
fun saveState(){
App.instance.savedBundle = navController.saveState()
Log.d(TAG, "saveState() : ${App.instance.savedBundle}")
}
}
here some logs: logs
full code:github

I am not sure if my answer helps you, but I had many issues trying to save the navigation state from handling rotations. The issue that I had comes from an old version of the navigation component, I update to the most recent, and it fixes the issue:
def android_navigation = '2.3.4'
implementation "android.arch.navigation:navigation-fragment-ktx:$android_navigation"
implementation "android.arch.navigation:navigation-ui-ktx:$android_navigation"
implementation "androidx.navigation:navigation-dynamic-features-fragment:$android_navigation"

How to change image in activity from fragment in Kotlin

In an android app I have an activity with several fragments. In one of these fragments I have an ImageButton. On click I want to let something happen in the activity directly, not in the fragment. In this case I want to set an image. Summed up, the ImageButton is in the fragment, but the ImageView I want to change on click is in the activity.
How do I achieve that? Whatever I've tried resulted in an app crash.
This is how my fragment.kt looks:
class Fragment1 : Fragment() {
companion object{
fun newInstance() = Fragment1()
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_1, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
imageButton.setOnClickListener{
imageView.setImageResource(R.drawable.example)
}
}
}

class Fragment1 : Fragment() {
var callbacks: OnFragmentCallbacks? = null
override fun onAttach(context: Context?) {
super.onAttach(context)
callbacks = activity as OnFragmentCallbacks
}
interface OnFragmentCallbacks{
fun changeImage(resourceId: Int)
}
companion object{
fun newInstance() = Fragment1()
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_1, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
imageButton.setOnClickListener{
callbacks?.changeImage(R.drawable.example)
}
}
In your Activity:
// Change FragmentName with name of your Fragment class
class MainActivity : AppCompatActivity(), FragmentName.OnFragmentCallbacks{
override fun changeImage(resouseId: Int){
imageView.setImageDrawable(getResources().getDrawable(resourceId))
// or
imageView.setImageResource(resourceId)
}
Just coded it in stackoverflow, may not be perfect

Trouble with NavController inside OnBackPressedCallback

I am getting a does not have a NavController set error inside a OnBackPressedCallback. Here is the code
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
fragmentView = inflater.inflate(R.layout.patient_info_fragment, container, false)
if(Utils.connectedToInternet()){
fragmentView.pastScreeningsButton.visibility = View.GONE
}
requireActivity().onBackPressedDispatcher.addCallback(object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
Navigation.findNavController(fragmentView).navigate(R.id.action_patientInfoFragment_to_patientsList)
}
})
setHasOptionsMenu(true)
return fragmentView
}
I am only getting this error when I come back into the fragment where this is implemented.
I have android:name="androidx.navigation.fragment.NavHostFragment" in the home fragment.
To clarify, I am using Navigation controller to do all my Navigation around my app and it works just fine. I only get this error inside this OnBackPressedCallback and only when the user navigates back into the fragment where this is implemented.
Let me know if you need to see any more of my code.

You might run into an issue with leaks of old instances of your fragment. Also it's not a good practice to store the created view within another variable like fragmentView. All in all your onCreateView implementation is doing too many things unrelated to its purpose.
I'd suggest to split up the functionality into relevant life-cycle methods and use the fragment.view directly within your callback. To not run into an issue with unattached views, you then bind and unbind the callback with the life-cycle.
class PatientInfoFragment: Fragment() {
private val callback = object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
Navigation.findNavController(view).navigate(R.id.action_patientInfoFragment_to_patientsList)
}
}
override fun onCreate(
savedInstanceState: Bundle?
) {
super.onCreate(savedInstanceState)
setHasOptionsMenu(true)
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View = inflater.inflate(R.layout.patient_info_fragment, container, false)
override fun onViewCreated(
view: View,
savedInstanceState: Bundle?
) {
if(Utils.connectedToInternet()){
view.pastScreeningsButton.visibility = View.GONE
}
}
override fun onStart() {
super.onStart()
requireActivity().onBackPressedDispatcher.addCallback(callback)
}
override fun onStop() {
callback.remove()
super.onStop()
}
}
The callback life-cycle binding can be bound with the fragment as lifecycle owner calling the other addCallback(LifecycleOwner, OnBackPressedCallback).
Additionally you could have a look into Android KTX and Kotlin Android Extensions to simplify your implementation.

Move your code in the onViewCreated and pass the view that is provided by the overriden method:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
requireActivity().onBackPressedDispatcher.addCallback(object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
Navigation.findNavController(view).navigate(R.id.action_patientInfoFragment_to_patientsList)
}
})
}
If that also doesn't work, replace the .navigate() with popBastack(R.id.framgment_where_you_want to go, false), in case your previous fragment stays on the backStack