FAB with anchor in coordinator layout has extra margin in android pre-lollipop

Question

I have a CoordinatroLayoutwith FloatingActionButton. Here is my code:

<android.support.design.widget.CoordinatorLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/toolbar_layout"
        android:layout_above="@+id/actionbar">

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

            <android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="120dp"
                android:minHeight="?android:attr/actionBarSize"
                android:background="@color/toolbar_color" />


            <ScrollView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"

                >

            </ScrollView>


        </LinearLayout>

        <android.support.design.widget.FloatingActionButton
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:clickable="true"
            app:fabSize="mini"
            android:src="@mipmap/ic_action_edit"
            app:layout_anchor="@id/toolbar"
            app:layout_anchorGravity="bottom|right|end"
            app:backgroundTint="@color/toolbar_color"            />
        </android.support.design.widget.CoordinatorLayout>

But it appears differently in lollipop and pre-lollipop devices.

Lollipop:

Pre-Lollipop:

Actually I haven't add any margin. But FAB has margin in pre-lollipop devices.

I have also seen this problem in cheessesquare sample. It shows different margins too. What is the problem?

Answer 1

I dont think you want to place them without margins. If I understood it right, you've done this to see whats going on in different versions of android.

You can use app:useCompatPadding="true" and remove custom margins to maintain same margins across different versions of android

Proof of concept

Answer 2

According to this link, it seems to be a bug in android design library. It says that:

in API <20, the button renders its own shadow, which adds to the overall logical width of the view, whereas in API >=20 it uses the new Elevation parameters which don't contribute to the view width.

So I have to provide two resource files for margin:

res/values:

<dimen name= "fab_margin_right">0dp</dimen>

And in res/values-v21:

<dimen name = "fab_margin_right">8dp</dimen>