How to create a Custom Notification Layout in android?

Use a custom contentView on your Notification Builder

To define a custom notification layout, start by instantiating a
RemoteViews object that inflates an XML layout file. Then, instead of
calling methods such as setContentTitle(), call setContent(). To set
content details in the custom notification, use the methods in
RemoteViews to set the values of the view’s children:

Create an XML layout for the notification in a separate file. You
can use any file name you wish, but you must use the extension .xml
In your app, use RemoteViews methods to define your notification’s icons and text. Put this RemoteViews object into your
NotificationCompat.Builder by calling setContent(). Avoid setting a
background Drawable on your RemoteViews object, because your text
color may become unreadable.

custom_push.xml has my custom views R.id.image,R.id.text,R.id.title

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout"
    android:layout_width="fill_parent"
    android:layout_height="64dp"
    android:padding="10dp" >
    <ImageView
        android:src="https://stackoverflow.com/questions/41888161/@mipmap/ic_launcher"
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_alignParentLeft="true"
        android:layout_marginRight="10dp" />
    <TextView
        android:textSize="13dp"
        android:textColor="#000"
        android:text="Testing"
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/image"
        />
    <TextView
        android:textSize="13dp"
        android:textColor="#000"
        android:text="Testing is awecome"
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/image"
        android:layout_below="@id/title"
         />
</RelativeLayout>

Instantiating a RemoteViews object and set it,

RemoteViews contentView = new RemoteViews(getPackageName(), R.layout.custom_push);
contentView.setImageViewResource(R.id.image, R.mipmap.ic_launcher);
contentView.setTextViewText(R.id.title, "Custom notification");
contentView.setTextViewText(R.id.text, "This is a custom layout");

NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this)
.setSmallIcon(R.drawable.icon)
.setContent(contentView);

Notification notification = mBuilder.build();
notification.flags |= Notification.FLAG_AUTO_CANCEL;
notification.defaults |= Notification.DEFAULT_SOUND;
notification.defaults |= Notification.DEFAULT_VIBRATE;
notificationManager.notify(1, notification);

check : https://developer.android.com/guide/topics/ui/notifiers/notifications.html#ApplyStyle