eclipse中为什么显示不出来左右按钮

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/src-com.example.titlebar"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.titlebar.MainActivity" >
 
    <com.example.titlebar.TopBar
 
        android:layout_height="50dp"
        android:layout_width="match_parent"
        android:id="@+id/topbar"
       
        custom:leftBackground="@color/black"
        custom:leftText="Bcak"
        custom:leftTextColor="#ffffff"
       
        custom:rightBackground="@color/green"
        custom:rightText="More"
        custom:rightTextColor="#ffffff"
       
        custom:titleTextSize="10sp"
        custom:title="自定义标题"
        custom:titletTextColor="#123412" >       
    </com.example.titlebar.TopBar>