Call Prefix Filter takes source code from a lot of different places. The internet community deserves much credits. A lot of individuals generously share their knowledge.
The AppCompatDelegate sample code is found in Stack Overflow.
The file picker dialog box is based on Roger Keays' article.
The sample code is posted by Uncle Code Monkey.
The Java reflection code is posted by Vincent Hiribarren.
https://stackoverflow.com/questions/32345768/cannot-resolve-method-setlatesteventinfo
Cindy Potvin's article points out the use of MediaScannerConnection.
https://blog.cindypotvin.com/saving-data-to-a-file-in-your-android-application/