no gravity for scrollview. how to make content inside scrollview as center

I had the same issue and finally figured it out. This is for a vertical ScrollView.

Put your ScrollView inside a RelativeLayout and center it in the RelativeLayout. In order for this to work, your ScrollView should have

android:layout_height="wrap_content"

This is how the final code should look like:

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

    <ScrollView
        android:id="@+id/scrollView1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" 
        android:layout_centerVertical="true" >

        <LinearLayout
            android:id="@+id/linearLayout1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            <Button
                android:id="@+id/button1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="b1"/>
            <Button
                android:id="@+id/button2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="b2"/>
            <Button
                android:id="@+id/button3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="b3"/>
        </LinearLayout>

    </ScrollView>

</RelativeLayout>