Center Horizontal doesn't work

Question

I'm trying to set the position of imagebutton in center, but it doesn't work.

Now when I try to set it to center it goes nearly to right.

Can someone show me where I've made a mistake in my codes?

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:background="#EBEBEB" >
    <LinearLayout
    android:id="@+id/layout"
    android:layout_width="match_parent"
    android:layout_height="fill_parent"
    android:layout_gravity="center_horizontal"
    android:gravity="center_horizontal"
    android:orientation="vertical">

        <RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="fill_parent"
    android:gravity="center"
    android:background="#EBEBEB" >
        <ImageView
        android:id="@+id/imagefield"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:layout_marginTop="5dp"
        android:src="@drawable/imagefield"
        android:background="@null"/>
    <ImageButton
        android:id="@+id/imageButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@null"
        android:onClick="imagebutton1"
        android:layout_alignBottom="@+id/imagefield"
        android:layout_centerHorizontal="true"
        />   
        <ProgressBar
         android:id="@+id/progressBar1"
         style="?android:attr/progressBarStyleHorizontal"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_above="@+id/imagebutton1"/> 



</RelativeLayout>
</LinearLayout>
</ScrollView>

Answer 1

COPY PASTE BELOW CODE

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:background="#EBEBEB" >

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:background="#EBEBEB" >

        <ImageView
            android:id="@+id/imagefield"
            android:layout_width="200dp"
            android:layout_height="200dp"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="5dp"
            android:background="@null"
            android:src="@drawable/ic_action_chat" />

        <ImageButton
            android:id="@+id/imageButton1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:onClick="imagebutton1" />

        <ProgressBar
            android:id="@+id/progressBar1"
            style="?android:attr/progressBarStyleHorizontal"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@+id/imagefield"
            android:layout_alignTop="@+id/imagefield"
             />

    </RelativeLayout>

</ScrollView>