Develop Reference

What is a view model and how can I use it to replace findViewById with View Binding and

I am working on a basic bluetooth app in android studio and I am having trouble with view binding. So far I have this in my MainActivity.kt
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
...
Later in the onCreate I have this line
val btnONOFF = findViewById<View>(R.id.btnONOFF) as Button
and I would like to replace the findViewById using viewbinding but I'm not sure what to replace that line with.
The android developers website says to use something like this
binding.name.text = viewModel.name
but I'm also not sure what a viewModel is.
Here is my ViewFragment.kt incase that is helpful
class ViewFragment : Fragment() {
private var _binding: ActivityMainBinding? = null
private val binding get() = _binding!!
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): RelativeLayout {
_binding = ActivityMainBinding.inflate(inflater, container, false)
return binding.root
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}}
Any help is appreciated, thanks!

You can find the tutorial of viewmodel from here.
ViewFragment.kt
class ViewFragment : Fragment() {
private var _binding: ActivityMainBinding? = null
private val binding get() = _binding!!
private val viewModel by viewModel<ActivityViewModel>()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): RelativeLayout {
_binding = ActivityMainBinding.inflate(inflater, container, false)
setupView()
return binding.root
}
private fun setupView(){
binding.text = viewModel.name
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
You can customise your ActivityViewModel.kt
class ActivityViewModel : ViewModel() {
val name = "Hello"
}
Note: by viewModel is koin injection.

Using Binding for accessing UI element of parent activity from fragment

So, I am trying to migrate from kotlin synthetic to Jetpack view binding.
Here is the kotlin synthetic code (works fine) that simply set visibility to invisible of TextView in the parent activity from fragment.
import kotlinx.android.synthetic.main.activity_main.*
class FirstFragment : Fragment() {
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(R.layout.fragment_first, container, false)
requireActivity().textView.visibility = View.INVISIBLE
return view
}
}
And here is what I'm doing to migrate:
import com.mypc.myapp.databinding.FragmentFirstBinding
import com.mypc.myapp.databinding.ActivityMainBinding
class FirstFragment : Fragment() {
private var _binding: FragmentFirstBinding? = null
private val binding get() = _binding!!
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentFirstBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.textView.visibility = View.INVISIBLE
binding.textview.setOnClickListener {
Navigation.findNavController(view).navigate(R.id.goto_secondfragment)
}
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
I'm getting error as 'Unsolved reference' at 'textview':
binding.textView.visibility = View.INVISIBLE
And at:
binding.textview.setOnClickListener {
Navigation.findNavController(view).navigate(R.id.goto_secondfragment)
}
Obviously the compiler is not able to find TextView that is in Activity
I've added this line:
import com.mypc.myapp.databinding.ActivityMainBinding

Since your binding is private to MainActivity you can refer to your textView from the MainActivity only. To show/hide this view from FirstFragment you can create a public function in MainActivity and call it from your FirstFragment.
class MainActivity: AppCompatActivity {
private var _binding: ActivityMainBinding? = null
private val binding get() = _binding!!
fun showHideTextView(visible: Boolean) {
binding.textView.isVisible = visible
}
}
And in your fragment, you can call:
(requireActivity() as MainActivity).showHideTextView(false) // This will hide the textView

First of all, you should define instance of activity view binding in baseActivity which is a parent class of your MainActivity, and then define method to change your text view like 'showTextView' , after that in the base fragment class initalize base activity instance with casting context object in onAttach method.
I provide you some code:
abstract class BaseRegisterActivity : BaseActivity() {
//---
protected lateinit var binding: ActivityRegisterBinding
private val navHostFragment by lazy {
supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as
NavHostFragment
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = DataBindingUtil.setContentView(this, R.layout.activity_register)
//---
}
fun showTextView() {
binding.textView.visibility = View.VISIBLE
binding.textView.setOnClickListener {
val fragment =
navHostFragment.childFragmentManager.fragments[0]
if (fragment is FirstFragment) {
//todo
}
}
}
}
abstract class BaseFragment : Fragment(), Injectable {
//--
lateinit var baseActivity: BaseRegisterActivity
override fun onAttach(context: Context) {
super.onAttach(context)
baseActivity = context as BaseRegisterActivity
}
//--
}

class ShopFragment : Fragment() {
var binding:FragmentShopBinding ?= null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
binding = FragmentShopBinding.inflate(inflater,container,false)
return binding?.root
}

BottomSheetDialogFragment.viewBinding

I struggle to do a property delegate for ViewBinding on BottomSheets.
The general Idea is similar to this
For Fragments i use something like this
fun <T : ViewBinding> Fragment.viewBinding(viewBindingFactory: (View) -> T) =
FragmentViewBindingDelegate(this, viewBindingFactory)
On BottomSheetsDialogFragments which are Fragments it does not accept the delegate.
fun <T : ViewBinding> BottomSheetDialogFragment.viewBinding(viewBindingFactory: (View) -> T) =
FragmentViewBindingDelegate(this, viewBindingFactory)
The Lifecycle of BottomSheets would be the same as on regular Fragments, so i would not expect any problems.
Anyone came up with a solution on this ?

You can still use the FragmentViewBindingDelegate and extension from Gabor.
You just also need to inflate the view inside onCreateView().
For example:
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.google.android.material.bottomsheet.BottomSheetDialogFragment
import com.zhuinden.fragmentviewbindingdelegatekt.viewBinding
class ExampleBottomSheet : BottomSheetDialogFragment() {
//Using ::bind here since the view is already inflated in onCreateView()
private val binding by viewBinding(YourCustomViewBinding::bind)
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.your_custom_view, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//Use binding here or wherever you need it
}
}

Implement ViewBinding in BottomSheetFragment like this (Works for me):
class CustomBottomSheet : BottomSheetDialogFragment() {
private lateinit var binding: CustomBottomSheetBinding
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
binding = CustomBottomSheetBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//onClick listener
binding.button.setOnClickListener {
Toast.makeText(context, "Clicked", Toast.LENGTH_LONG).show()
}
}
}

This works:
class CampaignBottomSheet : BottomSheetDialogFragment() {
private var _binding: MenuCampaignsBinding? = null
private val binding get() = _binding!!
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
_binding = MenuCampaignsBinding.inflate(layoutInflater)
binding.startCampaign.setOnClickListener { println("__print::CampaignBottomSheet") }
return binding.root
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}

Unlike Fragment class, BottomSheetDialogFragment doesn't have a constructor that accepts layout resource.
You can create a custom dialog for it. Basically, copy everything from AppCompatDialogFragment and BottomSheetDialogFragment.

Where to Initialize lateinit ? Giving error "kotlin.UninitializedPropertyAccessException: lateinit property db has not been initialized"

MainActivity.kt
class MainActivity : AppCompatActivity() {
lateinit var db:Database
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
db=Room.databaseBuilder(applicationContext,Database::class.java,"Users").build() //Error is shown here
}
}
AddUserFragment.kt
class AddUserFragment : Fragment() {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
val view= inflater.inflate(R.layout.fragment_add_user, container, false)
view.btn_add.setOnClickListener {
val id=et_Uid.text.toString()
val name=et_Name.text.toString()
val email=et_Email.text.toString()
val users=Users(id,name,email)
val mainActivity=MainActivity()
mainActivity.db.myDao().addUser(users) //Error is shown here
Toast.makeText(activity,"Added",Toast.LENGTH_LONG).show()
}
return view
}}
Where to initialize db so not to get kotlin.UninitializedPropertyAccessException: lateinit property db has not been initialized

You are creating fresh instance of MainActivity which is not required!
Every Fragment has the activity instance which they associated with
Just cast that activity as MainActivity
(activity!! as MainActivity).db.myDao().addUser(users)

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