FAB isn't floating

Question

The activity layout is a bit complex... it's a fragment activity, the bottom fragment ('bottomBarFragmentPlaceholder') is the bottomAppBar where the FAB is placed in the middle.

The activity layout is as follows:

<?xml version="1.0" encoding="utf-8"?><!-- practice_activity.xml -->
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

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

        <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <ProgressBar
                android:id="@+id/progressBar"
                style="?android:attr/progressBarStyleHorizontal"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_alignTop="@id/progressBarTimeText"
                android:layout_alignBottom="@id/progressBarTimeText"
                android:scaleY="6" />

            <TextView
                android:id="@+id/progressBarTimeText"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_centerHorizontal="true"
                android:background="#00000000"
                android:gravity="center" />
        </RelativeLayout>

        <androidx.viewpager.widget.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/pager"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1" />

        <FrameLayout
            android:id="@+id/bottomBarFragmentPlaceholder"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </LinearLayout>

</FrameLayout>

Then the BottomAppBar layout is as follows:

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/bottomBarLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="false">

    <com.google.android.material.bottomappbar.BottomAppBar
        android:id="@+id/bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:background="@color/primaryLightColor"
        android:backgroundTint="@color/primaryLightColor"
        app:fabAlignmentMode="center"
        app:menu="@drawable/ic_action_overflow"
        app:navigationIcon="@drawable/ic_menu_24"
        app:popupTheme="@style/ThemeOverlay.MaterialComponents.Dark"
        app:theme="@style/ThemeOverlay.MaterialComponents.ActionBar" />

        <com.google.android.material.floatingactionbutton.FloatingActionButton
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:src="@drawable/baseline_publish_black_24dp"
            app:layout_anchor="@id/bar" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>

Why is my FAB being pushed down instead of fitting into the cradle?

Any help would be very much appreciated.

thanks, GBa.

The FAB is centered in its parent. To place it inside the "white hole" you have to set FAB parent with taller height. To let you understand: try to set "id/bar" Height to "400dp" instead of "wrap_content" and you'll see the FAB moving accordling. — emandt, Jan 04 '19 at 09:33
That's true and will do the job in placing the FAB in the right place. However, this will have a different implication, the place assigned to the upper content will be shorter and as you can see it has grey-ish background (can be seen when looked carefully inside the "white hole" as you call it... or cradle...). I could set the same background color for the bottomappbar as well, however, the real impact is that the content of this upper widget will flow only up to the button and not around it... I would expect it to flow up to the bottomAppBar since the button is floating ain't it? — GBa, Jan 04 '19 at 12:37
Try to replicate as much as possible the example: https://medium.com/material-design-in-action/implementing-bottomappbar-material-components-for-android-f490c4a01708 — emandt, Jan 04 '19 at 13:07
Well, that's exactly the tutorial I've followed... and BTW, the FAB in material design indeed is floating... see here https://material.io/design/components/app-bars-bottom.html#behavior — GBa, Jan 04 '19 at 13:28
Try to remove your "android:layout_gravity="center"" from the FAB. The tutorial doesn't seems to use it — emandt, Jan 04 '19 at 13:33

score 0 · Accepted Answer · answered Jan 04 '19 at 15:02

Well, played around with the different layouts until I finally got it all set...

Key insights:

The FrameLayout which is required to allow overlay capabilities (floating button) is not needed in the upper levels but only in the lowest possible level... (see updated layouts below)
The bottomAppBar layout cannot be with layout_height="wrap_content", it needs to be given the ability to take all space of the parent... ("match_parent"), that's how the FAB will be given enough height to be placed correctly in the cradle.

Finally, here are the updated layouts:

The Fragment Activity layout is as follows:

<?xml version="1.0" encoding="utf-8"?><!-- practice_activity.xml -->

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <ProgressBar
            android:id="@+id/progressBar"
            style="?android:attr/progressBarStyleHorizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignTop="@id/progressBarTimeText"
            android:layout_alignBottom="@id/progressBarTimeText"
            android:scaleY="6" />

        <TextView
            android:id="@+id/progressBarTimeText"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:background="#00000000"
            android:gravity="center" />
    </RelativeLayout>

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <androidx.viewpager.widget.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/pager"
            android:layout_width="match_parent"
            android:layout_gravity="center|fill_vertical"
            android:layout_height="match_parent" />

        <FrameLayout
            android:id="@+id/bottomBarFragmentPlaceholder"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="bottom"/>
    </FrameLayout>
</LinearLayout>

The BottomAppBar layout is as follows:

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/bottomBarLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="false">

    <com.google.android.material.bottomappbar.BottomAppBar
        android:id="@+id/bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:background="@color/primaryLightColor"
        android:backgroundTint="@color/primaryLightColor"
        app:fabAlignmentMode="center"
        app:menu="@drawable/ic_action_overflow"
        app:navigationIcon="@drawable/ic_menu_24"
        app:popupTheme="@style/ThemeOverlay.MaterialComponents.Dark"
        app:theme="@style/ThemeOverlay.MaterialComponents.ActionBar" />

        <com.google.android.material.floatingactionbutton.FloatingActionButton
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/baseline_publish_black_24dp"
            app:layout_anchor="@id/bar" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>

I hope that this helps others that will face similar issues in the future...

Happy coding... GBa.

FAB isn't floating

1 Answers1