Create a function for a button that is inside a fragment - kotlin

Question

I've made an app with 4 fragments, each of which represents the app page. Now, inside one of the fragments I've got a ToggleButton. I am trying to get OnClickListener so that it changes the button's background colour once clicked. I'm coding this in my MainActivity.kt and not in the Fragments. However, it crashes the app without logcat.
package com.example.myassignment
import android.graphics.Color
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.fragment.app.Fragment
import com.example.myassignment.Fragments.DestinationsFragment
import com.example.myassignment.Fragments.HelpFragment
import com.example.myassignment.Fragments.HomeFragment
import com.example.myassignment.Fragments.SettingsFragment
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.fragment_settings.*
class MainActivity : AppCompatActivity() {
private val helpFragment = HelpFragment()
private val settingsFragment = SettingsFragment()
private val homeFragment = HomeFragment()
private val destinationsFragment = DestinationsFragment()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
replaceFragment(homeFragment)
bottom_navigation.setOnNavigationItemSelectedListener{
when(it.itemId){
R.id.ic_home -> replaceFragment(homeFragment)
R.id.ic_destinations -> replaceFragment((destinationsFragment))
R.id.ic_help -> replaceFragment(helpFragment)
R.id.ic_settings -> replaceFragment(settingsFragment)
}
true
}
// This is the onclick for the button which is inside a fragment (SettingsFragment)
btnReset.setOnClickListener { resetColour() }
}
// Function for the onclick function
private fun resetColour() {
btnReset.setBackgroundColor(Color.parseColor("#3E3E3E"))
}
private fun replaceFragment(fragment: Fragment){
if (fragment !=null){
val transaction = supportFragmentManager.beginTransaction()
transaction.replace(R.id.fragment_container, fragment)
transaction.commit()
}
}
}
And here's my SettingsFragment code (I haven't changed anything)
package com.example.myassignment.Fragments
import android.graphics.Color
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.example.myassignment.R
import kotlinx.android.synthetic.main.fragment_settings.*
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"
/**
* A simple [Fragment] subclass.
* Use the [SettingsFragment.newInstance] factory method to
* create an instance of this fragment.
*/
class SettingsFragment : Fragment() {
// TODO: Rename and change types of parameters
private var param1: String? = null
private var param2: String? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
param1 = it.getString(ARG_PARAM1)
param2 = it.getString(ARG_PARAM2)
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_settings, container, false)
}
companion object {
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* #param param1 Parameter 1.
* #param param2 Parameter 2.
* #return A new instance of fragment SettingsFragment.
*/
// TODO: Rename and change types and number of parameters
#JvmStatic
fun newInstance(param1: String, param2: String) =
SettingsFragment().apply {
arguments = Bundle().apply {
putString(ARG_PARAM1, param1)
putString(ARG_PARAM2, param2)
}
}
}
}
Here's the XML for the fragment, the button I'm trying to change is btnReset
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
xmlns:app="http://schemas.android.com/apk/res-auto"
tools:context=".Fragments.SettingsFragment"
android:background="#color/black">
<TextView
android:id="#+id/txtSettings"
android:layout_width="323dp"
android:layout_height="102dp"
android:layout_marginTop="16dp"
android:background="#color/orange"
android:gravity="center"
android:text="Settings"
android:textAlignment="center"
android:textColor="#color/black"
android:textSize="60sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="#+id/txtNotifications"
android:layout_width="223dp"
android:layout_height="48dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="12dp"
android:layout_marginRight="12dp"
android:background="#color/grey"
android:gravity="center"
android:text="Notifications"
android:textAlignment="center"
android:textColor="#color/black"
android:textSize="20sp"
app:layout_constraintEnd_toStartOf="#+id/btnNotifications"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/txtSettings" />
<TextView
android:id="#+id/txtNightMode"
android:layout_width="223dp"
android:layout_height="48dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="12dp"
android:layout_marginRight="12dp"
android:background="#color/grey"
android:gravity="center"
android:text="Night Mode"
android:textAlignment="center"
android:textColor="#color/black"
android:textSize="20sp"
app:layout_constraintEnd_toStartOf="#+id/btnNightMode"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/txtNotifications" />
<TextView
android:id="#+id/txtWIFI"
android:layout_width="223dp"
android:layout_height="48dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="12dp"
android:layout_marginRight="12dp"
android:background="#color/grey"
android:gravity="center"
android:text="WI-FI Only"
android:textAlignment="center"
android:textColor="#color/black"
android:textSize="20sp"
app:layout_constraintEnd_toStartOf="#+id/btnWIFI"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/txtNightMode" />
<ToggleButton
android:id="#+id/btnNotifications"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="44dp"
android:layout_marginRight="44dp"
android:text="ToggleButton"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#+id/txtSettings"
android:background="#color/cyan"
/>
<ToggleButton
android:id="#+id/btnNightMode"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="44dp"
android:layout_marginRight="44dp"
android:checked="false"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#+id/btnNotifications"
android:background="#color/cyan"
/>
<ToggleButton
android:id="#+id/btnWIFI"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="44dp"
android:layout_marginRight="44dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#+id/btnNightMode"
android:background="#color/cyan"/>
<Button
android:id="#+id/btnReset"
android:layout_width="337dp"
android:layout_height="154dp"
android:layout_marginTop="24dp"
android:text="Reset"
android:background="#color/cyan"
android:backgroundTint="#color/orange"
android:textColor="#color/black"
android:textSize="50sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/txtWIFI" />
</androidx.constraintlayout.widget.ConstraintLayout>
----- Edit -----
New SettingsFragment code:
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
btnReset.setOnClickListener { resetColour() }
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_settings, container, false)
}
private fun resetColour() {
btnReset.setBackgroundColor(Color.parseColor("3E3E3E"))
}
Here's the logcat
2021-02-17 08:20:32.594 11717-11717/com.example.myassignment E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myassignment, PID: 11717
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.myassignment.Fragments.SettingsFragment.onCreateView(SettingsFragment.kt:40)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2600)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
at androidx.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

Answer 1

This line is your problem.
btnReset.setOnClickListener { resetColour() }
btnReset lives in your fragment, but you are trying to reference it from your activity. Try moving that code to the fragment which inflates the view that btnReset lives in.
See the line import kotlinx.android.synthetic.main.fragment_settings.* in your activity class? This is what made it seem like btnReset was a valid property to reference in your activity. You should delete that line.
Lastly, it's very unlikely that this 'crashed without logcat'. You probably have some sort of filter on your logcat that's preventing you from seeing the crash.