Looking good so far.
I got confused on which way the row was sliding at first.
Was wondering about the blanks, if they could be filled by pushing others in maybe.
I have been hashing out something similar to this, but using all lettered tiles.
Checking for valid words is a limitation for me, so I am supplying a predefined list of words to use rather than any word in the dictionary.
I see you limited it to one word, which is a good way to start.
My only worry here, is that there may be too many squares in your grid to port to phones, but I guess you can have fewer squares for that version and keep the bigger one for tablets and PCs.
I am trying to limit mine to an 8x8 grid, but I am still scratching ideas out on paper and have nothing done in working code yet.
Well on your way here, so keep at it.
Using AppGameKit V1 Tier 1