To center a view in Framelayout, there are some available tricks. The simplest one I used for my Webview and Progressbar(very similar to your two object layout), I just added android:layout_gravity="center"
Here is complete XML in case if someone else needs the same thing to do
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".WebviewPDFActivity"
android:layout_gravity="center"
>
<WebView
android:id="@+id/webView1"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
<ProgressBar
android:id="@+id/progress_circular"
android:layout_width="250dp"
android:layout_height="250dp"
android:visibility="visible"
android:layout_gravity="center"
/>
</FrameLayout>
Here is my output