Solve Sudoku

This is my first crack at developing Android apps. So, any feedback is most welcome and greatly appreciated! (Although positive feedback is preferred :)

Solve Sudoku will solve any Sudoku puzzle you throw at it (even a blank puzzle!), as long as there is at least one solution. There are three main features:

1) What Goes Here?
Pressing this will solve the puzzle, but will only show you the value of the Sudoku cell where your cursor is pointed. Use this if you're stumped, and want the answer for one particular cell!

2) Next Step
Pressing this will solve the puzzle, and show you the first step that the app took to solve the puzzle. Each consecutive press will show you the next step in the app's solution. Red numbers indicate that the app had to guess at that location, blue numbers indicate that the app used logic to determine what number goes there. Cell's with gray background indicate that when the app guessed at that location, the guess was wrong, and it should use another guess in that location.

Right now, the app uses two main strategies to solve a Sudoku before it resorts to guessing. Because of this, the number of steps could be 3000+ for some harder puzzles. In later versions, I'll probably try to add some other logic strategies to use before it starts guessing.

3) Solve
This does just what you expect: solves the puzzle and gives you all the answers!