android 布局relativeLayout实现底部标签

<?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"
>

<RelativeLayout
android:layout_width="match_parent"
android:layout_height="60dp"
android:layout_alignParentBottom="true"
android:background="#000"
>
<RelativeLayout
android:id="@+id/rl"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="10dp"
android:background="#f00"
>
</RelativeLayout>
<ImageButton
android:id="@+id/ib"
android:layout_width="60dp"
android:layout_height="60dp"
android:background="@drawable/gonggao"
android:layout_centerInParent="true"
/>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_toLeftOf="@+id/ib"
android:layout_alignTop="@+id/rl"
>
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:background="@drawable/ic_launcher"
/>
</RelativeLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_toRightOf="@+id/ib"
android:layout_alignTop="@+id/rl"
>
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:background="@drawable/ic_launcher"
/>
</RelativeLayout>
</RelativeLayout>

</RelativeLayout>