Floating Action Button is not displaying - viewpager

Question

I read some posts here about this problem, but I couldn't get display the FAB. I tried different ways, but I don't really what's going on.

<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:fitsSystemWindows="true">

<android.support.design.widget.AppBarLayout
    android:id="@+id/app_bar_layout"
    android:layout_width="match_parent"
    android:layout_height="112dp"
    android:background="@color/colorPrimary"
    android:elevation="@dimen/elevation_toolbar"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    android:fitsSystemWindows="true">

    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/collapsing_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:contentScrim="@color/colorPrimary"
        app:expandedTitleMarginEnd="64dp"
        app:expandedTitleMarginStart="48dp"
        app:layout_scrollFlags="scroll|enterAlways"
        android:fitsSystemWindows="true">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?actionBarSize"
            android:layout_marginLeft="@dimen/list_toolbar_side_margin"
            android:layout_marginRight="@dimen/list_toolbar_side_margin"
            app:layout_collapseMode="pin" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            style="@style/AppTabLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom"
            app:tabGravity="fill"
            app:tabMode="fixed"
            app:tabTextAppearance="@style/AppTabTextAppearance"/>

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

</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_id"
    android:layout_width="60dp"
    android:layout_height="60dp"
    android:layout_gravity="end|bottom"
    android:layout_margin="16dp"
    android:clickable="true"
    android:src="@drawable/ic_add"
    />

If it checks the preview in android studio, the fab is there. Even, when I debug the app, I can see that the fab is created.

I attempted too using a app:layout_anchor="@id/viewpager" or app:layout_anchor="@id/app_bar_layout" with **app:layout_anchorGravity="bottom|right" ** and it didn't work. The FAB is covered by the viewpager. How can I avoid that?

I attach an image of the main activity. You will see a button "add plant". This button should be replaced by the FAB.

Answer 1

Try this in ur xml

app:layout_anchor="@id/viewpager"
app:layout_anchorGravity="bottom|right"

and remove

android:layout_gravity="end|bottom"

Answer 2

Try to insert the floatingActionButton into frameLayout and insert this layout to your main layout.. it works for me

<android.support.constraint.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
   .
   .
   .

   <FrameLayout
       android:id="@+id/rootLayout"
       android:layout_width="match_parent"
       android:layout_height="match_parent">

       <android.support.design.widget.FloatingActionButton
           android:id="@+id/fab_add_room"
           android:layout_width="wrap_content"
           android:layout_marginBottom="8dp"
           android:layout_marginRight="8dp"
           android:layout_height="wrap_content"
           android:layout_gravity="bottom|right"
           android:src="@drawable/ic_add"
           app:fabSize="normal" />

  </FrameLayout>
  .
  .
  .
</android.support.constraint.ConstraintLayout>