Toolbar not displaying from inside collapsing toolbar

Question

Here is the code.

<?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"
    android:id="@+id/main"
    android:layout_height="match_parent"
    android:layout_width="match_parent">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="100dp">

        <android.support.design.widget.CollapsingToolbarLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="scroll|enterAlways|exitUntilCollapsed">

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

            <android.support.design.widget.TabLayout
                android:id="@+id/main_tablayout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="bottom"
                app:layout_collapseMode="none"/>


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

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

    <!--<android.support.v4.widget.NestedScrollView-->
        <!--android:id="@+id/nestedscroll"-->
        <!--android:layout_width="match_parent"-->
        <!--android:layout_height="match_parent"-->
        <!--android:fillViewport="true"-->
        <!--android:scrollbars="horizontal"-->
        <!--app:layout_behavior="@string/appbar_scrolling_view_behavior">-->

            <android.support.v4.view.ViewPager
                android:id="@+id/main_viewpager"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                app:layout_behavior="@string/appbar_scrolling_view_behavior"/>

    <!--</android.support.v4.widget.NestedScrollView>-->

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/main_fab"
        android:layout_margin="16dp"
        android:src="@android:drawable/ic_media_play"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_anchor="@id/main_viewpager"
        app:layout_anchorGravity="bottom|end"/>

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

The problem:
1) Toolbar is not visible.
2) Collapsing toolbar doesn't collapse at all. [Solved]
3) Viewpager and FAB also not visible if put inside nestedScrollView. [Solved]

Extra detail:
Layout for fragments of Viewpager have Linearlayout as root and inside that have a recyclerview.

Everything seems to be alright as per the code. Unable to understand what is missing. A good explanation of how coordinator layout and collapsing toolbar work together would also indeed help.

Answer 1

1) Toolbar is not visible.

First of all you need define what Toolbar do you want to use in your activity class:

 Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
 setSupportActionBar(toolbar);

Change existing xml code:

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="?attr/colorPrimary"
            app:title="@string/app_name"
            app:layout_collapseMode="parallax">
        </android.support.v7.widget.Toolbar>

to:

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"  //set initial height
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" //this might be also useful
            app:title="@string/app_name"
            app:layout_collapseMode="parallax" />

2) Collapsing toolbar doesn't collapse at all.

Did your activity using correct theme. Set to your AppBarLayout:

android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"

as in this example: include_list_viewpager.xml

3) Viewpager and FAB also not visible if put inside nestedScrollView.

There's no reason to do that. Adding these lines:

android:layout_marginTop="?attr/actionBarSize" 
app:layout_behavior="@string/appbar_scrolling_view_behavior" 

to ViewPager should be enough.

Both of them should be direct children of CoordinatorLayout.

Follow this example: http://blog.nkdroidsolutions.com/collapsing-toolbar-with-tabs-android-example/

If you're new to Material Design or feel a bit lost with some its behaviours, I highly recommend to check Chris Banes Material Design project cheesequare: https://github.com/chrisbanes/cheesesquare/

Hope it will help