notification bar is not showing in android

Question

so I made a simple app of how notification work on android I use NotificationManager for making the simple notification app is work with setOnclick and I use PendingIntent.

I was run my app and is not show anything, I got some bug in this case

this is my MainActivity.kt :

    import android.app.Notification
    import android.app.NotificationChannel
    import android.app.NotificationManager
    import android.app.PendingIntent
    import android.content.Context
    import android.content.Intent
    import android.graphics.Color
    import android.os.Build
    import androidx.appcompat.app.AppCompatActivity
    import android.os.Bundle
    import android.widget.Button
    import kotlinx.android.synthetic.main.activity_main.*
    
    class MainActivity : AppCompatActivity() {
    
        lateinit var notificationManager: NotificationManager
        lateinit var notificationChannel: NotificationChannel
        lateinit var builder: Notification.Builder
    
        val channelId = "com.example.notiffication"
    
        val description = "My Notification"
    
        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
    
            val show = findViewById<Button>(R.id.btn_show)
    
            notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
            show.setOnClickListener {
    
    
                val intent = Intent()
    
                val pendingIntent =
                    PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
    
    
    
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                    notificationChannel =
                        NotificationChannel(channelId, description, NotificationManager.IMPORTANCE_HIGH)
    
                    notificationChannel.enableLights(true)
                    notificationChannel.lightColor = Color.RED
                    notificationChannel.enableVibration(true)
  notificationManager.notify(0, builder.build())
    
                    notificationManager.createNotificationChannel(notificationChannel)
    
                    builder = Notification.Builder(this, channelId)
                        .setContentTitle("Android")
                        .setContentText("New Message")
                        .setSmallIcon(R.mipmap.ic_launcher)
                        .setContentIntent(pendingIntent)
    
                } else {
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                        builder = Notification.Builder(this)
                            .setContentTitle("Android")
                            .setContentText("New Message")
                            .setSmallIcon(R.mipmap.ic_launcher)
                            .setContentIntent(pendingIntent)
                    }
              
                }
    
            }
    
        }
    }

this is my main_activity.xml :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">


    <Button
        android:id="@+id/btn_show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="250dp"
        android:layout_centerHorizontal="true"
        android:text="Show Notification" />

</RelativeLayout>

this is my logcat :

 kotlin.UninitializedPropertyAccessException: lateinit property builder has not been initialized
        at com.example.notiffication.MainActivity.getBuilder(MainActivity.kt:20)
        at com.example.notiffication.MainActivity$onCreate$1.onClick(MainActivity.kt:53)
        at android.view.View.performClick(View.java:7448)
        at android.view.View.performClickInternal(View.java:7425)
        at android.view.View.access$3600(View.java:810)
        at android.view.View$PerformClick.run(View.java:28296)
        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)

and for the method Notification.Builder I use old version

Answer 1

Now the problem is that you are calling the notify method before build the notification.

Your activity should looks like this

class MainActivity : AppCompatActivity() {

    companion object {
        private const val CHANNEL_ID = "default_channel"
        private const val CHANNEL_NAME = "My Notification"
        private const val NOTIFICATION_ID = 123
    }

    private val notificationManager by lazy {
        getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val btnShow = findViewById<Button>(R.id.btn_show)
        btnShow.setOnClickListener {
            createChannel()
            val notification = buildNotification()
            notificationManager.notify(NOTIFICATION_ID, notification)
        }
    }

    private fun buildNotification(): Notification {
        val intent = Intent()
        val pendingIntent = PendingIntent
            .getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
        return NotificationCompat.Builder(this, CHANNEL_ID)
            .setContentTitle("Android")
            .setContentText("New Message")
            .setSmallIcon(R.mipmap.ic_launcher)
            .setContentIntent(pendingIntent)
            .build()
    }

    private fun createChannel() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val channel =
                NotificationChannel(CHANNEL_ID, CHANNEL_NAME, NotificationManager.IMPORTANCE_HIGH)
            channel.enableLights(true)
            channel.lightColor = Color.RED
            channel.enableVibration(true)
            notificationManager.createNotificationChannel(channel)
        }
    }
    
}

You can learn more about notifications here:

• Official documentation
• Official codelab
• Official course