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>

I think a more elegant solution would be to use the ScrollView's android:fillViewport property. A ScrollView is a little different in how it treats it's content view (can only have one), even if you set match_parent (fill_parent) to the ScrollView it won't give that much spacing to it's content view, instead the default behavior is for the ScrollView to wrap the content regardless of what you specify for that view. What android:fillViewport does is tell the ScrollViewto stretch its content to fill the viewport (http://developer.android.com/reference/android/widget/ScrollView.html#attr_android:fillViewport). So in this case, your LinearLayout would be stretched to match the viewport and if the height goes behind the viewport then it will be scrollable which is exactly what you want!

The accepted answer won't work properly when the content extends beyond the ScrollView because it will still center the content view first causing it to cut off a portion of the view, and the ScrollView centered in another layout works but just doesn't feel right, besides I think it will also result in a lint error (useless parent or something along those lines).

Try something like this:

<ScrollView
    android:id="@+id/scroller"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:paddingTop="12dp"
    android:paddingBottom="20dp"
    android:scrollbarStyle="outsideOverlay"
    android:fillViewport="true">

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

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="check" />

    </LinearLayout>

</ScrollView>

Just remember that the reason it is being centered here now is because of the android:gravity on the LinearLayout since the ScrollView will stretch the LinearLayout so keep that in mind depending on what you add to the layout.

Another good read on ScrollView although not about centering but about fillViewport is http://www.curious-creature.org/2010/08/15/scrollviews-handy-trick/

How about this?

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/scrollView1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:paddingTop="12dp"
    android:paddingBottom="20dp"
    android:scrollbarStyle="outsideOverlay" >


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

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="check" 
            android:gravity="center_vertical|center_horizontal"/>
    </LinearLayout>

</ScrollView>