[android] How to create a horizontal loading progress bar?

Just add a STYLE line and your progress becomes horizontal:

<ProgressBar
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/progress"
        android:layout_centerHorizontal="true"      
        android:layout_centerVertical="true"      
        android:max="100" 
        android:progress="45"/>