eclipse中為什么顯示不出來左右按鈕

<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="自定義標題"
??????? custom:titletTextColor="#123412" >???????
??? </com.example.titlebar.TopBar>