android - FAB animation with viewpager/tabslider

Question

I'm trying to find way to achieve such effect https://material-design.storage.googleapis.com/publish/material_v_4/material_ext_publish/0B6Okdz75tqQsVlhxNGJCNTEzNFU/components-buttons-fab-behavior_04_xhdpi_009.webm

I'm using android.support.v4.view.ViewPager

I appreciate any hints and help

Answer 1

First, you need to have the layout with the floating action button anchored to the ViewPager:

<android.support.design.widget.CoordinatorLayout
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

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

        <android.support.v7.widget.Toolbar
            android:id="@+id/action_bar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@android:color/white"
            app:tabGravity="center"
            app:tabIndicatorColor="?attr/colorAccent"
            app:tabMode="scrollable"
            app:tabSelectedTextColor="?attr/colorAccent"
            app:tabTextColor="@android:color/black" />

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

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

     <android.support.design.widget.FloatingActionButton
            android:id="@+id/fab"
            app:layout_anchor="@id/viewpager"
            app:layout_anchorGravity="bottom|right|end"
            android:layout_width="56dp"
            android:layout_height="56dp"
            android:src="@drawable/ic_add_white"
            app:borderWidth="@dimen/fab_border_width"
            app:fabSize="normal" />

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

Now that you have the FAB anchored to the ViewPager (note: I've tried this on a fragment that is a tab in the viewpager; it does not seem to behave properly), add an OnPageChangeListener to your ViewPager like so:

 viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        }

        @Override
        public void onPageSelected(int position) {

            switch (position) {
                case INDEX_OF_TAB_WITH_FAB:
                    fab.show();
                    break;

                default:
                    fab.hide();
                    break;
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

The animations for the "pop" and the "shrink" upon switching tabs are handled automatically for you with the new version of the Support Library.