Develop Reference

Kotlin Change ViewText with an ID provided by a String

Goal: To get a ViewText resource and edit it from an activity, using a mutable string (because then the string can be changed to alter other ViewTexts in the same function).
Context: I'm making a grid using TableRows and TextViews that can be altered to form a sort of map that can be generated from an array.
Issue: The binding command does not recognise strings. See my comment "PROBLEM HERE".
Tried: getResources.getIdentifier but I've been told that reduces performance drastically.
An excerpt from gridmap.xml
<TextView
android:id="#+id/cell1"/>
GridMap.kt
package com.example.arandomadventure
import android.R
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.example.arandomadventure.databinding.GridmapBinding
class GridMap : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//sets the binding and assigns it to view
val binding: GridmapBinding = GridmapBinding.inflate(layoutInflater)
val view = binding.root
setContentView(view)
//creates a string variable
var cellID = "cell1"
//uses binding to set the background colour to teal
binding.cellID.setBackgroundResource(R.color.teal_200) //<- PROBLEM HERE (Unresolved Reference)
//getResources.getIdentifier is not an option as it degrades performance on a larger scale
}
}

A binding object is just an autogenerated class, whose class members are defined by the views in your layout XML. You can't add or access a field on a class with the syntax you showed - binding classes are no different from any other class. If you wanted to be able to access them by name, you could load them into a map
val viewMap = mapOf(
"cell1" to binding.cell1,
"cell2" to binding.cell2,
"cell3" to binding.cell3
)
then you can use the map to access them by name
var cellID = "cell1"
viewMap[cellID].setBackgroundResource(R.color.teal_200)
If you want the map to be a class member, you can set it like this
private lateinit var viewMap: Map<String,View>
override fun onCreate(savedInstanceState: Bundle?) {
//...
viewMap = mapOf(
"cell1" to binding.cell1,
"cell2" to binding.cell2,
"cell3" to binding.cell3
)
}
If your layout has hundreds of views and this becomes cumbersome, you may want to consider adding the views programmatically instead.
Edit
If you want to do this a more ugly, but more automatic way you can use reflection. To do this you need to add this gradle dependency:
implementation "org.jetbrains.kotlin:kotlin-reflect:1.7.0"
then you can build up the map programmatically with all views in the binding.
val viewMap = mutableMapOf<String,View>()
GridmapBinding::class.members.forEach {
try {
val view = it.call(binding) as? View
view?.let { v ->
viewMap[it.name] = v
}
}
catch(e: Exception) {
// skip things that can't be called
}
}
Or you can use this to call a method (keep in mind this will throw if no such class member exists):
var cellID = "cell1"
val view = GridmapBinding::class.members.filter { it.name == cellID }[0].call(binding)

Can't change the value of MutableList in a Kotlin class

I want to add the random generated integer into my MutableList in Player class when I use the random integer generator method located in Player class in my fragment then I want to pass this MutableList to Fragment with using Livedata(I'm not sure if i'm doing right with using livedata).Then show the MutableList in TextView.But MutableList returns the default value not after adding.
So what am i doing wrong ? What should i do ?
Thank you
MY CLASS
open class Player {
//property
private var playerName : String
private var playerHealth : Int
var playerIsDead : Boolean = false
//constructor
constructor(playerName:String,playerHealth:Int){
this.playerName = playerName
this.playerHealth = playerHealth
}
var numberss: MutableList<Int> = mutableListOf()
fun attack(){
//Create a random number between 1 and 10
var damage = (1..10).random()
//Subtract health points from the opponent
Log.d("TAG-DAMAGE-WRITE","$damage")
numberss.add(damage)
Log.d("TAG-DAMAGE-ADD-TO-LIST","$numberss")
Log.d("TAG-NUMBER-LIST-LATEST-VERSION","$numberss")
}
}
MY FRAGMENT
class ScreenFragment : Fragment() {
var nickname : String? = null
private lateinit var viewModel : DenemeViewModel
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_screen, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = ViewModelProvider(this).get(DenemeViewModel::class.java)
arguments?.let {
nickname = ScreenFragmentArgs.fromBundle(it).nickName
}
sFtextView.text = "Player : $nickname"
action()
}
private fun action(){
val health1 = (1..50).random()
val health2 = (1..50).random()
val superMan = Superman("Dusman",health1,)
while(superMan.playerIsDead == false){
//attack each other
superMan.attack()
sFtextsonuc.text = "Superman oldu"
viewModel.setData()
observeLiveData()
superMan.playerIsDead = true
}
}
fun observeLiveData(){
viewModel.damageList.observe(viewLifecycleOwner, Observer { dmgList ->
dmgList?.let {
sFtextsonuc.text = it.toString()
Log.d("TAG-THE-LIST-WE'VE-SENT-TO-FRAGMENT","$it")
}
})
}
}
MY VIEWMODEL
class DenemeViewModel : ViewModel() {
val damageList:MutableLiveData<MutableList<Int>> = MutableLiveData()
fun setData(){
damageList.value = Superman("",2).numberss
Log.d("TAG-VIEWMODEL","${damageList.value}")
}
}
MY LOG
PHOTO OF THE LOGS

Your Superman is evidently part of some ongoing game, not something that should be created and then destroyed inside the action function. So you need to store it in a property. This kind of state is usually stored in a ViewModel on Android so it can outlive the Fragment.
Currently, you are creating a Superman in your action function, but anything created in a function is automatically sent do the garbage collector (destroyed) if you don't store the reference in a property outside the function.
Every time you call the Superman constructor, such as in your line damageList.value = Superman("",2).numberss, you are creating a new instance of a Superman that has no relation to the one you were working with in the action() function.
Also, I recommend that you do not use LiveData until you fully grasp the basics of OOP: what object references are, how to pass them around and store them, and when they get sent to the garbage collector.
So, I would change your ViewModel to this. Notice we create a property and initialize it with a new Superman. Now this Superman instance will exist for as long as the ViewModel does, instead of only inside some function.
class DenemeViewModel : ViewModel() {
val superman = Superman("Dusman", (1..50).random())
}
Then in your frgament, you can get this same Superman instance anywhere you need to use it, whether it be to deal some damage to it or get the current value of its numberss to put in an EditText.
Also, I noticed in your action function that you have a while loop that repeatedly deals damage until Superman is dead. (It also incorrectly observes live data over and over in the loop, but we'll ignore that.) The problem with this is that the while loop is processed to completion immediately, so you won't ever see any of the intermediate text. You will only immediately see the final text. You probably want to put some delays inside the loop to sort of animate the series of events that are happening. You can only delay easily inside a coroutine, so you'll need to wrap the while loop in a coroutine launch block. In a fragment when working with views, you should do this with viewLifecycleOwner.lifecycleScope.launch.
Finally, if you set playerIsDead to true on the first iteration of the loop, you might as well remove the whole loop. I'm guessing you want to wrap an if-condition around that line of code. But since your code above doesn't modify player health yet, there's no sensible way to determine when a player should be dead, so I've commented out the while loop
private fun action() = viewLifecycleOwner.lifecycleScope.launch {
val superMan = viewModel.superman
//while(superMan.playerIsDead == false){
//attack each other
superMan.attack()
sFtextsonuc.text = "Superman oldu"
delay(300) // give user a chance to read the text before changing it
sFtextsonuc.text = superMan.numberss.joinToString()
delay(300) // give user a chance to read the text before changing it
// TODO superMan.playerIsDead = true
//}
}

In Android Kotlin, what's the right way to pass a onclick event into a viewholder?

Is there any difference in these two ways?
I've been using the seond way and it works so far, yet I found the first way upon reading tutorial articles.
1st:
class FlowersAdapter(private val onClick: (Flower) -> Unit) :
ListAdapter<Flower, FlowersAdapter.FlowerViewHolder>(FlowerDiffCallback) {
/* ViewHolder for Flower, takes in the inflated view and the onClick behavior. */
class FlowerViewHolder(itemView: View, val onClick: (Flower) -> Unit) :
RecyclerView.ViewHolder(itemView) {
private val flowerTextView: TextView = itemView.findViewById(R.id.flower_text)
private val flowerImageView: ImageView = itemView.findViewById(R.id.flower_image)
private var currentFlower: Flower? = null
init {
itemView.setOnClickListener {
currentFlower?.let {
onClick(it)
}
}
}
/* Bind flower name and image. */
fun bind(flower: Flower) {
currentFlower = flower
flowerTextView.text = flower.name
if (flower.image != null) {
flowerImageView.setImageResource(flower.image)
} else {
flowerImageView.setImageResource(R.drawable.rose)
}
}
}
}
First way of writing
2nd:
class FlowerViewHolder(itemView: View) :
RecyclerView.ViewHolder(itemView) {
private val flowerTextView: TextView = itemView.findViewById(R.id.flower_text)
private val flowerImageView: ImageView = itemView.findViewById(R.id.flower_image)
private var currentFlower: Flower? = null
/* Bind flower name and image. */
fun bind(flower: Flower) {
currentFlower = flower
flowerTextView.text = flower.name
if (flower.image != null) {
flowerImageView.setImageResource(flower.image)
} else {
flowerImageView.setImageResource(R.drawable.rose)
}
itemView.setOnClickListener {
onClick(flower)
}
}
}
Second way of writing
Appreicate your time and effort in telling me the differences.

From the perceptive of separation of concern, all the clickListeners are supposed to be handled in the Activity or Fragment and Adapters are meant just to wrap around the items, in your case Flower and present them in a way which can be used by the RecyclerView to display on the screen.
With that being said, the core logic of clickListeners is to be moved out of the bind method into the activity/fragment and that's precisely whats the firstMethod is all about. Matter of fact, I haven't noticed any performance improvement by employing the FirstMethod over the second one yet I insist on using FirstOne because its more of code organizing.

IMHO I feel like the adapter should know nothing about click listeners or any details about the ViewHolder; so I wouldn't pass the callback through the adapter.
I like passing the callback to my ViewHolder but instead of mapping into the init block I do it on the onBind hook from the adapter where I receive the view as a parameter. Also, I pass or update the ViewHolders directly into my Adapters. And then have some generic functions to compute whether the data-set has changed or not.
If you do it like this, you have the benefit that you may build 1 generic adapter and use it elsewhere without really minding how many different types of ViewHolder you may have to implement later on as it is completely agnostic.
TLDR;
So based on what you've provided us I would use the good things of both approaches. Binding the callback into the bind hook and passing the callback through the constructor of the ViewHolder

How can I iterate over all views known to the data binder?

I have three TextInputEditText views in my layout where the user can type in specific information.
On the click of a Button this information is stored in my database.
After the user clicks this Button, I want to clear all TextInputEditText fields.
Right now, I am doing this by hardcoding:
private fun clearAllEditTextFields() {
Timber.d("clearAllEditTextFields: called")
binding.bookTitleEditText.text = null
binding.bookAuthorEditText.text = null
binding.bookPageCountEditText.text = null
}
Since this is bad, I would like to use a dynamic for each loop to identify all views of type TextInputEditText known to binding and clear their content:
private fun clearAllEditTextFields() {
Timber.d("clearAllEditTextFields: called")
for (view in binding.views) {
if (view is TextInputEditText) {
view.text = null
}
}
Unfortunately, there is no such field binding.views.
Is there still a way to achieve this or something with the same properties?
What I have tried so far
I have used a BindingAdapter. In my Util class, where all my extension functions go, I have created an EditText extension function clearText annotated as BindingAdapter and JvmStatic:
#JvmStatic
#BindingAdapter("clearText")
fun EditText.clearText(#NotNull shouldClear: Boolean) {
Timber.d("clearText: called")
if (shouldClear) text = null
}
In XML:
<com.google.android.material.textfield.TextInputEditText
android:id="#+id/book_title_edit_text"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:imeActionId="100"
android:imeOptions="actionNext"
android:inputType="text"
android:text="#={viewModel.bookTitle}"
app:clearText="#{viewModel.clearAllEditTextFields}"
/>
In my ViewModel class, I have created a var clearAllEditTextFields = false which is modified in the clearAllEditTextFields() function which gets called inside my ViewModel:
...
var clearAllEditTextFields = false
clearAllEditTextFields()
...
private fun clearAllEditTextFields() {
Timber.d("clearAllEditTextFields: called")
clearAllEditTextFields = true
}
According to Logcat, my extension function is called when my ViewModel is initialized. However, when clearAllEditTextFields() gets called, it does not trigger a new call to the extension function.

A simple for loop doesn't exist to loop over the views in the binding object and you can try the following to keep your code conscice.
Scope Functions
binding.apply{
bookTitleEditText.text = null
bookAuthorEditText.text = null
bookPageCountEditText.text = null
}
scope functions are a good go iff there are few views and we end up with quite a boiler-plate code if the number of views is large, in which cases I think Binding-Adapter would be a good choice
#BindingAdapter("clear_text")
fun EditText.clearText(shouldClear : Boolean?){
shouldClear?.apply{
if(shouldClear)
text = null
}
}
ViewModel
private val _shouldClear = MutableLiveData<Boolean>()
val shouldClear : LiveData<Boolean>
get() = _shouldClear
fun setClearStatus(status : Boolean){
_shouldClear.value = status
}
//since clearing a text is an event and not state, reset the clear_status once it's done
fun resetClearStatus(){
_shouldClear.value = nul
}
XML
<EditText
......
app:clear_text = "#{yourViewModel.shouldClear}"
...... />
ActivityClass
...
binding.lifecycleOwner = this
...
private fun clearAllEditTextFields() {
yourViewModel.setClearStatus(true)
yourViewModel.resetClearStatus()
}
Edit:
add binding.lifecycleOwner = this in your activity class and its used for observing LiveData with data binding. The view will observe for text changes at runtime.

Create a linearlayout (or similar) called, for example, text_fields_linear layout enclosing all of your textfields. then do:
private fun clearAllEditTextFields() {
for (item in binding.textFieldsLinearLayout) {
item.text = null
}
}

Why this strange behaviour of the `by lazy` delegate in fragments

A few days ago, I posted this question about using synthetic properties when you include the same layout in a screen multiple times.
The answer was awesome but after I tried it more for a few days, I noticed a strange behaviour:
When going forward from the fragment (the one containing the references to the view obtained by the lazy delegate) and then coming back ( I use transaction.commit() and manager.popBackStack(), to do this ), the labels will be empty. I already checked with the debugger if anything is null there, and nothing is.
The only solution that seems to work is replacing the by lazy with lateinit var and assigning them in onViewCreated.
Do you know why? Is the solution I used still "good" as a kotlin idiom?
I include the two pieces of code for the sake of completeness:
Partially working one:
private val foundTitle by lazy { detailContainer1.title }
private val foundDescription by lazy { detailContainer1.description }
private val wantedTitle by lazy { detailContainer2.title }
private val wantedDescription by lazy { detailContainer2.description }
Always working one:
private lateinit var foundTitle: TextView
private lateinit var foundDescription: TextView
private lateinit var wantedTitle: TextView
private lateinit var wantedDescription: TextView
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
foundTitle = detailContainer1.title
foundDescription = detailContainer1.description
wantedTitle = detailContainer2.title
wantedDescription = detailContainer2.description
}
Thanks in advance

Fragment's have their view destroyed when they get removed - but lazy fields do not clear their reference so they are essentially leaking previous view.
If possible You should always have unique view IDs within your project, even if they are not within same layout - having duplicates can cause multiple problems (like yours).
If you were able to use kotlin extensions directly, it would generate code for finding, caching and clearing the view cache when fragments view is destroyed automatically.
Try to "get" views from fragments cache instead of assigning them to fields:
private val foundTitle
get() = detailContainer1.title
private val foundDescription
get() = detailContainer1.description
private val wantedTitle
get() = detailContainer2.title
private val wantedDescription
get() = detailContainer2.description