Good day, y'all!
Today I was doing the Google Codelabs for Kotlin. I'm trying to use findViewById() in a function but it shows as an unresolved reference. I bet it's a fairly easy problem but I can't figure it out. this is my code
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
findViewById<Button>(R.id.done_button).setOnClickListener { addNickname(it) }
}
}
private fun addNickname(view: View) {
val editText = findViewById<EditText>(R.id.nickname_edit)
val nicknameTextView = findViewById<TextView>(R.id.nickname_text)
nicknameTextView.text = editText.text
nicknameTextView.visibility = View.VISIBLE
editText.visibility = View.GONE
view.visibility = View.GONE
}
When I try to assign the editText and the nickmaneTextView vals to the views I use findViewById() but it shows as unresolved reverence.
it's quite basic so I don't know where is the issue
I'll be very grateful for your help
Edit:
if I use
val editText = view.findViewById<EditText>(R.id.nickname_edit)
val nicknameTextView = view.findViewById<TextView>(R.id.nickname_text)
I get an error saying that the nicknameTextView is null and it crashes
You should add view
val editText = view.findViewById<EditText>(R.id.nickname_edit)
val nicknameTextView = view.findViewById<TextView>(R.id.nickname_text)
Ok I figured it out, the fun must be created inside the
class MainActivity: AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
'here'
}
I knew it was a dumb problem :(
Thank you for your help
Related
I am a beginner ,https://i.stack.imgur.com/k8z9T.jpgin the android studio whenever I try to use findViewById.It shows an error and they ask me to create its variable but I don't know how to create it . Please tell me, I am stuck here.
You just created a function outside of your MainActivity. You have to create it inside of your activity. According to your screenshot, you just try to create a Top-level Function not a Function because it's outside of your activity. When you need to create a Function you have to create that inside your activity. Keep your eyes on Curley Brackets {}.
See the explanation to understand.
In your screenshot
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
} /* Your activity end's on here*/
private fun addNickName(view: View) {
// Your instance
// val editText = findViewById<EditText>(R.id.nickName_edit)
}
So the answer is
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
private fun addNickName(view: View) {
// Your instance
// val editText = findViewById<EditText>(R.id.nickName_edit)
}
} /* Your activity end's on here*/
Hope you understand!. Thank you
Hello all,
I am new to Kotlin and was trying to keep recreating my code to get it easier for me to learn. i have created an dice app and it works. but everytime i create a new project and start. I always get the error on findViewById(R.id.) i make the layout first with all the ID`s assigned but no matter what i do i keep getting this error. I use Android Studio.
I hope someone can help me get this frustration out of my head.I want to know why it keeps getting that error. thanks in advance.
package com.example.dicedicebaby
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
//button action`
val rollButton: Button = findViewById(R.id.button)
//action of the button when pressed.
rollButton.setOnClickListener{ stones()}
}
}
fun stones(){
//The normal dice
val fDice=Dice(6)
//D20
val dDice = Dice(20)
//action of dice roll
val dice = fDice.roll()
//D20 action
val secondDice = dDice.roll()
//view
val resultView: TextView = findViewById(R.id.dice)
resultView.text = dice.toString()
val secondView: TextView = findViewById(R.id.Ddice)
secondView.text = secondDice.toString()
}
//makes the dice a dice.
class Dice(private val numSides:Int){
fun roll():Int{
return (1..numSides).random()
}
}
The suggested approach is to migrate to view binding.
Plus, you should declare the stones() function inside the MainActivity class body:
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
//action of the button when pressed.
binding.rollButton.setOnClickListener{ stones() }
}
fun stones(){
//The normal dice
val fDice=Dice(6)
//D20
val dDice = Dice(20)
//action of dice roll
val dice = fDice.roll()
//D20 action
val secondDice = dDice.roll()
//view
binding.dice.text = dice.toString()
binding.Ddice.text = secondDice.toString()
}
}
I can run Code A in Android Studio, I hope to preview UI when I'm designing, so I added Code B to Code A.
But Code B can't work, why? How can I fix it?
Code A
class MainActivity : ComponentActivity() {
private val handleMeter by viewModels<HandleMeter>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
SoundMeterTheme {
Surface(color = MaterialTheme.colors.background) {
Greeting(handleMeter)
}
}
}
}
}
#Composable
fun Greeting(handleMeter: HandleMeter) {
...
}
Code B
#Preview(showBackground = true)
#Composable
fun DefaultPreview() {
SoundMeterTheme {
val handleMeter by viewModels<HandleMeter>()
Greeting(handleMeter)
}
}
Unfortunately, you can't.
Preview does not support creating ViewModels and NavHost yet, for our bad.
But what you can do instead is to use a fake data or a static data into ui, until the design finish and when you are ready to actually run it, replace the static data with the view model data.
You can use dagger and hilt to inject the view model constructor and then call up the hilt view model in the preview e.g.
#HiltViewModel
class DataFieldsViewModel #Inject constructor(
) : ViewModel() {
Then in your preview code for your composable
#Preview(showBackground = true)
#Composable
fun PreviewDataFieldsScreen() {
DataFieldsScreen(
navController = rememberNavController(),
viewModel = hiltViewModel()
)
}
Is there a way to save map/mutableMap into savedInstanceState?
other than using ViewModel functions. I'm curious to know his point...
thanks in advance
I worked on it. wonder why i didn't find anyone asking about this before, probably there are better ways. but in case that someone needs to know how this is done. i did it this way...
i used onSaveInstanceState to check if the map was initialized, then proceeded
override fun onSaveInstanceState(savedInstanceState: Bundle) {
super.onSaveInstanceState(savedInstanceState)
if (::answersMap.isInitialized){
val keys = (answersMap.keys).toIntArray()
val values = (answersMap.values).toBooleanArray()
savedInstanceState.putIntArray(KEYS, keys)
savedInstanceState.putBooleanArray(VALUE, values)
}
}
also on the onCreate function I retrieved the arrays and created the mutablemap i needed
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val keysArray = savedInstanceState?.getIntArray(KEYS) ?: IntArray(0)
val valuesArray = savedInstanceState?.getBooleanArray(VALUE) ?: BooleanArray(0)
answersMap = mutableMapOf<Int, Boolean>().apply {
for (i in keysArray.indices) this [keysArray[i]] = valuesArray[i]
}
in case you were wondering about the answerMap type
private lateinit var answersMap : MutableMap<Int, Boolean>
IT WORKED!!!
When defining a global android.widget variable, e.g. TextView, is it preferable to use lateinit or by lazy? I initially thought using by lazy would be preferred as its immutable but I'm not entirely sure.
by lazy example:
class MainActivity: AppCompatActivity() {
val helloWorldTextView by lazy { findViewById(R.id.helloWorldTextView) as TextView }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
updateTextView(helloWorldTextView)
}
fun updateTextView(tv: TextView?) {
tv?.setText("Hello?")
}
}
lateinit example:
class MainActivity: AppCompatActivity() {
lateinit var helloWorldTextView: TextView
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
helloWorldTextView = findViewById(R.id.helloWorldTextView) as TextView
updateTextView(helloWorldTextView)
}
fun updateTextView(tv: TextView?) {
tv?.setText("Hello?")
}
}
Are there any benefits of using one over the other when defining a global android.widget var/val? Are there any pitfalls with using by lazy to define a android.widget val? Is the decision just based on whether you want a mutable or immutable value?
There's one pitfall with by lazy. The widget property would be read-only and therefore technically final (in Java terms). But there's no documented guarantee that onCreate() is called only once for an instance. Also findViewById() could return null.
So using lateinit is preferable and you'll get an exception to tell you if the val was used before onCreate().
A third possibility would be Android synthetic properties. Then you don't need to worry about the variables at all.
import kotlinx.android.synthetic.main.activity_main.*
helloWorldTextView.text = "Hello?"