Fading action bar effect using the new Toolbar class from the support library

activity_main.xml

<FrameLayout 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"
    android:background="@null"
    tools:context=".MainActivity">

    <com.github.manuelpeinado.toolbartest.ObservableScrollView
        android:id="@+id/scrollview"
        android:text="@string/hello_world"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fillViewport="true">

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <ImageView
                android:id="@+id/header"
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:adjustViewBounds="true"
                android:src="@drawable/nyc" />

            <TextView
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:background="?android:colorBackground"
                android:padding="16dp"
                android:text="@string/loren_ipsum" />

        </LinearLayout>

    </com.github.manuelpeinado.toolbartest.ObservableScrollView>

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:layout_gravity="top"
        android:minHeight="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

</FrameLayout>

MainActivity.java

package com.github.manuelpeinado.toolbartest;

import android.graphics.Color;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.View;

import com.readystatesoftware.systembartint.SystemBarTintManager;


public class MainActivity extends ActionBarActivity implements OnScrollChangedCallback {

    private Toolbar mToolbar;
    private Drawable mActionBarBackgroundDrawable;
    private View mHeader;
    private int mLastDampedScroll;
    private int mInitialStatusBarColor;
    private int mFinalStatusBarColor;
    private SystemBarTintManager mStatusBarManager;


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

        mToolbar = (Toolbar) findViewById(R.id.toolbar);
        mActionBarBackgroundDrawable = mToolbar.getBackground();
        setSupportActionBar(mToolbar);

        mStatusBarManager = new SystemBarTintManager(this);
        mStatusBarManager.setStatusBarTintEnabled(true);
        mInitialStatusBarColor = Color.BLACK;
        mFinalStatusBarColor = getResources().getColor(R.color.primary_color_dark);

        mHeader = findViewById(R.id.header);

        ObservableScrollable scrollView = (ObservableScrollable) findViewById(R.id.scrollview);
        scrollView.setOnScrollChangedCallback(this);

        onScroll(-1, 0);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public void onScroll(int l, int scrollPosition) {
        int headerHeight = mHeader.getHeight() - mToolbar.getHeight();
        float ratio = 0;
        if (scrollPosition > 0 && headerHeight > 0)
            ratio = (float) Math.min(Math.max(scrollPosition, 0), headerHeight) / headerHeight;

        updateActionBarTransparency(ratio);
        updateStatusBarColor(ratio);
        updateParallaxEffect(scrollPosition);
    }

    private void updateActionBarTransparency(float scrollRatio) {
        int newAlpha = (int) (scrollRatio * 255);
        mActionBarBackgroundDrawable.setAlpha(newAlpha);
        mToolbar.setBackground(mActionBarBackgroundDrawable);
    }

    private void updateStatusBarColor(float scrollRatio) {
        int r = interpolate(Color.red(mInitialStatusBarColor), Color.red(mFinalStatusBarColor), 1 - scrollRatio);
        int g = interpolate(Color.green(mInitialStatusBarColor), Color.green(mFinalStatusBarColor), 1 - scrollRatio);
        int b = interpolate(Color.blue(mInitialStatusBarColor), Color.blue(mFinalStatusBarColor), 1 - scrollRatio);
        mStatusBarManager.setTintColor(Color.rgb(r, g, b));
    }

    private void updateParallaxEffect(int scrollPosition) {
        float damping = 0.5f;
        int dampedScroll = (int) (scrollPosition * damping);
        int offset = mLastDampedScroll - dampedScroll;
        mHeader.offsetTopAndBottom(-offset);

        mLastDampedScroll = dampedScroll;
    }

    private int interpolate(int from, int to, float param) {
        return (int) (from * param + to * (1 - param));
    }
}

styles.xml

<resources>

    <style name="AppTheme" parent="Theme.AppCompat.Light">

        <item name="windowActionBar">false</item>
        <item name="android:windowTranslucentStatus">true</item>
        <item name="android:fitsSystemWindows">true</item>

        <item name="colorPrimary">@color/primary_color</item>
        <item name="colorPrimaryDark">@color/primary_color_dark</item>
        <item name="colorAccent">#f77</item>

    </style>

</resources>

FYI: It's also possible to use the android.support.v4.widget.NestedScrollView bundled in the support library instead of com.github.manuelpeinado.toolbartest.ObservableScrollView.

I'm having the same issue with @ramswaroop, when I go back, the action opacity doesn't return to normal

@nathaliepl thanks for your help it solved my issue.In parent activity just needed to ad this code

public void onResume(){
    super.onResume();
    updateColor();

}

@TargetApi(Build.VERSION_CODES.JELLY_BEAN)
private void updateColor() {
    toolbarBackgroundDrawable.setAlpha(255); // 0% of transparency
    toolbar.setBackground(toolbarBackgroundDrawable);
}