The layout XML is :
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="@color/translucenter_dark" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="200dip"
>
<ProgressBar android:id="@+id/progressBar1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
></ProgressBar>
</LinearLayout>
</LinearLayout>
And the final layout is :

Why the progressBar was not put in center both vertically and horizontally. Is it a feature or a bug 🙂
You could give the linear layout enclosing the progress bar
android:gravity="center".This will make the progress bar centered.
It seems progress bar utilizes the ViewGroup.LayoutParams. This class does not support layout_gravity such as LinearLayout.LayoutParams. So you will require to use the gravity property of the parent linear layout. This is a pretty good explanation of gravity in android.