FastScrollList

A demo application for fast scroll feature of RecyclerView.

Approaches

This demo consists of 2 approaches

1. The first approach is ported from a library called LollipopContactsRecyclerViewFastScroller. It is simple, lightweight but lacks customization capabilities. More problematically, the xml has to declared one more view beside RecyclerView to achieve the purpose, it could be a little troublesome to modify such code in large codebase.
2. The second approach is a combination of the above-mentioned library and another library called RecyclerView-FastScroll. It not only keeps the simplicity of the original lib but also gains the ability of declaring only one view in xml layout. A considerable drawback is the fact that the drawing process, the popup for instance, is actually hardcoded and difficult to change.
3. The third approach is the default fast scroll feature of RecyclerView. This method does not include the bubble indicates first letter of current view. However, it should be added fairly easily.

Performance

The goal of this experiment is to create a fast-scroll feature for RecyclerView, without losing the smooth experience of the original RecyclerView. In other words, the rendering time of each frame should not exceed 16ms, in order to maintain 60fps standard.

Tested with Profile GPU Rendering enabled, the rendering time still depends on the number of contacts, yet only to a minor extent. It should only slightly exceed 16ms for typical situations (< 200) or lose 1 - 2 frames for larger database (~ 1000). Compared to other major commercial products, it is actually on par with the default Contact application of Android, and far more efficient than the Facebook Messenger application.

Screenshots showing the difference in performance between the default Contact application and the demo application

Note

• Keep in mind that this is only a Proof of Concept, not a usable library.
• The Performance section is tested mainly with the second approach.