Full Text Searching, The Book, and You!

The APK edition of The Busy Coder’s Guide to Android Development offers full-text searching, via a SearchView widget in the action bar. Typing in a search expression and pressing Enter (or clicking the magnifying glass button in the soft keyboard) will bring up a set of search results, consisting of a snippet of text surrounding the search hit, along with information regarding what chapter the snippet comes from. Tapping on an item in the list jumps you to the paragraph within the chapter corresponding to the snippet that you tapped upon.

This is all powered by SQLite and an FTS3 table.

Since this is FTS3, and not some crude hand-rolled full-text search system of my own, you get a nice search syntax, supporting:

  • simple terms
  • wildcards (e.g., List* to match ListView, ListActivity, …)
  • phrases (e.g., "balding guy")
  • AND, OR, NOT, and NEAR operators (e.g., dynamic NEAR fragment*)
  • parentheses to enforce operator priorities

And, FTS3 is very fast. Even with all the prose in the book indexed, results come back in less than a second on decent hardware.

The good news is that this did not dramatically increase the size of the APK file. Partially, that is because much of the APK bulk comes from images, which are not indexed. Also, the index does not currently include the source code boxes, only the contents of paragraphs and bullets.

I create the FTS3 table as part of my book mastering process. I write the book in a tweaked version of MultiMarkdown, and I have a series of Ruby scripts that generate (and further tweak) HTML from the MultiMarkdown sources. Other Ruby scripts turn that HTML into the PDF, EPUB, and APK editions (with the Kindle/MOBI edition coming from the EPUB edition via Amazon’s kindlegen tool). The Ruby script for creating the APK edition:

  • Creates an empty database with an empty FTS3 table
  • Scans through all of the HTML and records all paragraphs and bullets in that table
  • Packages the database in a ZIP file in assets/ of the project
  • Compiles the APK

The app itself then uses SQLiteAssetHelper to unpack the database and make it available for querying.

In a future book update, I will provide more coverage of using FTS3 from within Android, as well as using SearchView for conducting FTS3 searches.

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