FAB (floating action button) doesn't float

问题

I've tried to use the floatingactionbutton element but it doesn't float in UI layout, the floating button occupies part of the layout and isn't over the component, in my case is a viewpager,

button doesn't float

this is my layout:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context="com.frases.frases.FraseMain"
    android:orientation="vertical">

    <android.support.v7.widget.Toolbar
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/appbar"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:minHeight="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light" >

    </android.support.v7.widget.Toolbar>

    <android.support.design.widget.TabLayout
        android:id="@+id/sliding_tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabMode="fixed"/>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="@android:color/white" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:src="@android:drawable/ic_dialog_email" />


</LinearLayout>

回答1:

It's because you are using LinearLayout as the root layout. You need FrameLayout to stack elements over one another, and FAB needs to be the last child node because it needs to stay on top of every other views.

<FrameLayout>
  <LinearLayout>
    ...
  </LinearLayout>

  <!-- FAB be the last node inside FrameLayout here -->
  <android.support.design.widget.FloatingActionButton />
</FrameLayout>

回答2:

I don't think you have to use coordinator layout, you can simply use floating button with below code as well.

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

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/dashboard_bg"
xmlns:app="http://schemas.android.com/apk/res-auto">

<!-- here you can have your viewpager -->

 <android.support.design.widget.FloatingActionButton
    android:id="@+id/dashboardShowActionsFab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:elevation="4dp"
    app:fabSize="normal"
    android:layout_alignParentBottom="true"
    android:layout_alignParentRight="true"
    android:layout_marginRight="26dp"
    android:layout_marginBottom="16dp" />

 </RelativeLayout>

Hope this helps.

回答3:

use CoordinatorLayout like below:

<android.support.design.widget.CoordinatorLayout
    android:id="@+id/main_content"
    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.support.v7.widget.Toolbar
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/appbar"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:minHeight="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light" >

    </android.support.v7.widget.Toolbar>

    <android.support.design.widget.TabLayout
        android:id="@+id/sliding_tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabMode="fixed"/>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="@android:color/white" />

          <android.support.design.widget.FloatingActionButton
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:layout_gravity="bottom|right"
              android:layout_margin="16dp"
              android:src="@drawable/ic_done"
              app:layout_anchor="@id/lvToDoList"
              app:layout_anchorGravity="bottom|right|end" />

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

来源：https://stackoverflow.com/questions/38194370/fab-floating-action-button-doesnt-float