LinearLayout里面的空间居中对齐

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<LinearLayout
android:layout_width="match_parent"
android:layout_height="20dp"
android:orientation="horizontal" >

<ImageButton
android:id="@+id/ibToleft"
android:layout_width="20dp"
android:layout_height="match_parent"
android:src="@drawable/left"
android:layout_margin="1dp" />

<TextView
<span style="color:#ff0000;">android:layout_width="0dp"</span>
android:layout_height="wrap_content"
android:text="@string/about"
an<span style="color:#ff0000;">droid:layout_weight="1"</span>
<span style="color:#ff0000;">android:gravity="center"</span>
android:textSize="20sp"
/>

</LinearLayout>

<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitXY"
android:src="@drawable/splash" />

</LinearLayout>