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This is my layout xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/fragment_body"
android:fitsSystemWindows="true">

<include
 android:id="@+id/contextToolBar"
 layout="@layout/context_toolbar_layout" />

<android.support.v7.widget.RecyclerView
 android:id="@+id/list1"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:layout_below="@+id/contextToolBar"
 android:scrollbarSize="5dp"
 android:scrollbarThumbVertical="@color/scrollbarColor"
 android:scrollbars="vertical"
 app:layout_behavior="@string/appbar_scrolling_view_behavior" />

<ProgressBar
 android:id="@+id/delete_progress"
 style="@style/Widget.AppCompat.ProgressBar"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_centerHorizontal="true"
 android:layout_centerVertical="true"
 android:visibility="gone" />

It displays a grid of images in the recyclerview.
I can select a bunch of images & have an option to delete them.
The following is the delete logic:

public void deleteSelectedFiles(final Context context, final List<MediaModel> selectionList) 

 String confirmationMessage = getString(R.string.delete_confirm_message);

 new AlertDialog.Builder(context)
 .setTitle(getString(R.string.action_delete))
 .setMessage(confirmationMessage)
 .setIcon(android.R.drawable.ic_dialog_alert)
 .setPositiveButton(android.R.string.yes, (dialog, whichButton) -> 
 View progressBar = getActivity().findViewById(R.id.delete_progress);
 dialog.cancel();
 progressBar.setVisibility(View.VISIBLE);

 deleteFileList(selectionList, this.getActivity());

 progressBar.setVisibility(View.GONE);
 )
 .setNegativeButton(android.R.string.no, null).show();

I am expecting the progress bar to display in the foreground while the delete operation is going on. But it just doesn't show up. Any help would be highly appreciated.