Can't see progress bar

<com.vlonjatg.progressactivity.ProgressActivity xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/progressActivity"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/box_background"
    android:padding="12dp"
    style="@style/ProgressActivity">

    <ExpandableListView
        android:id="@+id/exp_lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:childDivider="@color/box_background"
        android:divider="@color/box_background"
        android:dividerHeight="12dp" />

</com.vlonjatg.progressactivity.ProgressActivity>

I am using above code but I can't see any loading progress bar after calling progressActivity.showLoading();

StackOverflow Question for more details http://stackoverflow.com/questions/38482537/cant-see-loading-progress-bar-using-progressactivity