activity_main.xmlMainActivity.javaApp.javanotification_collapsed.xmlnotification_expanded.xmlNotificationReceiver.javaAndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="showNotification"
        android:text="show"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.965" />

</android.support.constraint.ConstraintLayout>

package com.codinginflow.customnotificationexample;

import android.app.Notification;
import android.app.PendingIntent;
import android.content.Intent;
import android.support.v4.app.NotificationCompat;
import android.support.v4.app.NotificationManagerCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.RemoteViews;

import static com.codinginflow.customnotificationexample.App.CHANNEL_ID;

public class MainActivity extends AppCompatActivity {
    private NotificationManagerCompat notificationManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        notificationManager = NotificationManagerCompat.from(this);
    }

    public void showNotification(View v) {
        RemoteViews collapsedView = new RemoteViews(getPackageName(),
                R.layout.notification_collapsed);
        RemoteViews expandedView = new RemoteViews(getPackageName(),
                R.layout.notification_expanded);

        Intent clickIntent = new Intent(this, NotificationReceiver.class);
        PendingIntent clickPendingIntent = PendingIntent.getBroadcast(this,
                0, clickIntent, 0);

        collapsedView.setTextViewText(R.id.text_view_collapsed_1, "Hello World!");

        expandedView.setImageViewResource(R.id.image_view_expanded, R.drawable.lotti2);
        expandedView.setOnClickPendingIntent(R.id.image_view_expanded, clickPendingIntent);

        Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
                .setSmallIcon(R.drawable.ic_android)
                .setCustomContentView(collapsedView)
                .setCustomBigContentView(expandedView)
                //.setStyle(new NotificationCompat.DecoratedCustomViewStyle())
                .build();

        notificationManager.notify(1, notification);
    }
}

package com.codinginflow.customnotificationexample;

import android.app.Application;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.os.Build;

public class App extends Application {
    public static final String CHANNEL_ID = "exampleChannel";

    @Override
    public void onCreate() {
        super.onCreate();
        createNotificationChannel();
    }

    private void createNotificationChannel() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(
                    CHANNEL_ID,
                    "Example Channel",
                    NotificationManager.IMPORTANCE_HIGH
            );

            NotificationManager manager = getSystemService(NotificationManager.class);
            manager.createNotificationChannel(channel);
        }
    }
}

<?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="64dp"
    android:gravity="center"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_view_collapsed_1"
        style="@style/TextAppearance.Compat.Notification.Title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New Message!"
        android:textColor="@color/colorPrimary" />

    <TextView
        android:id="@+id/text_view_collapsed_2"
        style="@style/TextAppearance.Compat.Notification.Info"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Expand to show!" />

</LinearLayout>

<?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="256dp"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_view_expanded"
        style="@style/TextAppearance.Compat.Notification"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@android:color/holo_red_light"
        android:padding="8dp"
        android:text="This is a custom notification"
        android:textAlignment="center"
        android:textColor="#FFF" />

    <ImageView
        android:id="@+id/image_view_expanded"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop"
        android:src="@drawable/lotti" />

</LinearLayout>

package com.codinginflow.customnotificationexample;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.support.v4.app.NotificationManagerCompat;
import android.widget.Toast;

public class NotificationReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "Image clicked", Toast.LENGTH_SHORT).show();

        NotificationManagerCompat notificationManager = NotificationManagerCompat.from(context);
        notificationManager.cancel(1);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.customnotificationexample">

    <application
        android:name=".App"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <receiver android:name=".NotificationReceiver" />
    </application>

</manifest>