Android studio crashing after setOnClickListener - android-studio

Question

I want to create an app to download a song from an URL.
I made a Alertbox with EditText for the URL. This seems to work fine, but as soon as I want to assign the functions to the buttons inside the Alertbox, the app crashes as soon as I click on the Button to open the alertbox and I get a Nullpointer error.
See my cod below:
XML:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="10dp">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/url"
android:hint="Enter URL"
android:inputType="textPersonName"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/downloadbtn"
android:text="Download"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/pastebtn"
android:text="Paste"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/cancelbtn"
android:text="Cancel"/>
</LinearLayout>
Kotlin:
package com.example.mymusicapp
import android.annotation.SuppressLint
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.os.CancellationSignal
import android.view.LayoutInflater
import android.widget.Button
import android.widget.EditText
import android.widget.TextView
import androidx.appcompat.app.AlertDialog
//import the button didnt fix it: import com.example.mymusicapp.R.id.downloadbtn
class MainActivity : AppCompatActivity() {
#SuppressLint("MissingInflatedId")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val songbtn = findViewById<Button>(R.id.btnsong)
val downloadbtn = findViewById<Button>(R.id.downloadbtn)
val pastebtn = findViewById<Button>(R.id.pastebtn)
val cancelbtn = findViewById<Button>(R.id.cancelbtn)
songbtn.setOnClickListener{
val mDialogView = LayoutInflater.from (this). inflate(R.layout.url_dialog, null)
val mBuilder = AlertDialog.Builder(this)
.setView(mDialogView)
.setTitle("Download MP3")
val mAlertDialog = mBuilder.show()
/* as soon as I use this code, the app crashes after clicking the "btnsong":
downloadbtn.setOnClickListener {
mAlertDialog.dismiss()
}
}
}
}

Answer 1

You cannot access a button inside a dialog directly using findviewbyid.
val btn=mAlertDialog.findViewById<Button>(R.id.downloadbtn)
or
val builder = AlertDialog.Builder(this)
val view = layoutInflater.inflate(R.layout.custom_dialog, null)
builder.setView(view)
val dialog = builder.create()
dialog.show()
val button = dialog.findViewById<Button>(R.id.my_button)
button.setOnClickListener {
Log.d("TAG", "Clicked")
dialog.dismiss()
}