collapsing toolbar

MyActivity.kt

import kotlinx.android.synthetic.main.activity_details.toolbar

....
override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_details)

        setSupportActionBar(toolbar) // at xml
        supportActionBar?.setDisplayHomeAsUpEnabled(true)
  ....
}

myactivity.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/htab_appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fitsSystemWindows="true"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsing_toolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            app:contentScrim="?attr/colorPrimary"
            app:expandedTitleMarginStart="20dp"
            app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">

            <ImageView
                android:id="@+id/rssdetIcon"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:fitsSystemWindows="true"
                android:minHeight="160dp"
                android:scaleType="centerCrop"
                android:src="@drawable/burg1"
                app:layout_collapseMode="parallax" />

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>


    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <android.support.constraint.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <TextView
                android:id="@+id/rssdetTitle"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:gravity="start"
                android:paddingBottom="2dp"
                android:paddingEnd="4dp"
                android:paddingStart="@dimen/activity_horizontal_margin"
                android:paddingTop="2dp"
                android:text="Title"
                android:textColor="@color/colorText"
                android:textSize="20sp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <View
                android:id="@+id/rssdetDivTop"
                android:layout_width="0dp"
                android:layout_height="1px"
                android:background="@color/divider"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/rssdetTitle" />

            <TextView
                android:id="@+id/rssdetPubDate"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:gravity="start"
                android:paddingBottom="2dp"
                android:paddingEnd="4dp"
                android:paddingStart="@dimen/activity_horizontal_margin"
                android:paddingTop="2dp"
                android:text="34 min ago"
                android:textColor="@color/colorTextSecondary"
                android:textSize="14sp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/rssdetDivTop" />

            <View
                android:id="@+id/rssdetDivBottom"
                android:layout_width="0dp"
                android:layout_height="1px"
                android:background="@color/divider"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/rssdetPubDate" />

            <TextView
                android:id="@+id/rssdetText"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:gravity="start"
                android:paddingBottom="2dp"
                android:paddingEnd="4dp"
                android:paddingStart="@dimen/activity_horizontal_margin"
                android:paddingTop="2dp"
                android:text="RSS is a type of web feed which allows users to access updates to online content in a standardized, computer-readable format. These feeds can, for example, allow a user to keep track of many different websites in a single news aggregator. The news aggregator will automatically check the RSS feed for new content. RSS is a type of web feed which allows users to access updates to online content in a standardized, computer-readable format. These feeds can, for example, allow a user to keep track of many different websites in a single news aggregator. The news aggregator will automatically check the RSS feed for new content. RSS is a type of web feed which allows users to access updates to online content in a standardized, computer-readable format. These feeds can, for example, allow a user to keep track of many different websites in a single news aggregator. The news aggregator will automatically check the RSS feed for new content"
                android:textColor="@color/colorTextSecondary"
                android:textSize="14sp"
                android:textStyle="bold"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/rssdetDivBottom" />
        </android.support.constraint.ConstraintLayout>
    </android.support.v4.widget.NestedScrollView>


</android.support.design.widget.CoordinatorLayout>

styles.xml

// no actionbar! 
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
        <item name="windowActionBar">false</item>
        <item name="windowActionBarOverlay">true</item>
        <item name="windowNoTitle">true</item>
        <item name="android:windowBackground">@color/colorBackground</item>
    </style>