Like the desktop Sokoban++, Soko++ for Android also supports Solver plug-ins.
Soko++ calls the plug-ins with a specially defined intent action; nl.joriswit.sokosolver.SOLVE. This intent gets one extra string parameter called LEVEL. This is the level in XSB format. When you find a solution, set RESULT_OK as the activity result, and add a extra parameter called SOLUTION, with the UDLR string.
As an example, I have made a small app. This app contains all solutions to Soko++'s built in levels. The solutions are simply read from a resource file.
Download the Solver example from Google Play, and download the source code SokoBuiltInLevelSolutions-source-code.zip (public domain license). You can also view the source code on GitHub.
YASS is Brian Damgaard's Sokoban solver; I have ported it to Android.
You can download YASS.apk here. You can also download YASS from Google Play (The version on Google Play is slightly older). You can download the source code on GitHub (GPL license). You can download YASS for Windows on Brian's YASC site.
Festival is Yaron Shoham's Sokoban solver; I have ported it to Android.
You can download Festival.apk here. You can also download Festival from Google Play. You can download the source code on GitHub. You can download Festival for Windows on Yaron's Festival Solver site.