如何在导航抽屉中居中自定义布局？

我创建了一个导航抽屉并列出了菜单图标。之后，我必须在菜单列表的底部包含一个自定义布局。

活动_main.xml

    <?xml version="1.0" encoding="utf-8"?>
    <!-- Use DrawerLayout as root container for activity -->
    <android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:layout_gravity="http://schemas.android.com/tools"
        android:id="@+id/drawer_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">

        <!-- Layout to contain contents of main body of screen (drawer will slide over this) -->
        <FrameLayout
            android:id="@+id/content_frame"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                ndroid:layout_height="?attr/actionBarSize"
                app:titleTextColor="@color/white"
                android:background="?attr/colorPrimary"
                ndroid:theme="@style/ThemeOverlay.AppCompat.ActionBar" />

        </FrameLayout>
   <!-- Container for contents of drawer - use NavigationView to make configuration easier -->
    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:menu="@menu/drawer_view_menu"
        app:headerLayout="@layout/nav_header"/>
 </android.support.v4.widget.DrawerLayout>

drawer_view_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <group android:checkableBehavior="single">
        <item
            android:id="@+id/nav_prof"
            android:title="@string/my_profile" />
           ........other items here.......
        </group>
      <group android:checkableBehavior="single">
        <item app:actionLayout="@layout/toggle_button"
            android:title="@string/blank"
            />
    </group>

切换按钮.xml

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

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/left_rounded"
    android:backgroundTint="@color/red"
    android:text="@string/lang_en"
    android:textColor="@color/white"/>

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/right_rounded"
    android:text="@string/lang_ar" />

然后它显示了自定义布局，但它在右侧对齐。我需要将其水平居中对齐。下面还附上了一张问题图。

问题说明