title: how to put 9 buttons in 3 rows in android xml layout?
body: <p>Im trying to make a tic-tac-toe game(android version).
  I want to make all the 9 buttons auto-sizing regarding to the width and the height of the device and put them evenly in a 3*3 grid. But I can only set the number for their sizes now.
  Can anyone tell me how to let them use the height and width of the parent and calculate their sizes?</p>
  
  <p>Also, im using the grid layout now. Is this the best layout I should use for the tic-tac-toe game?</p>
  
  <p>Thanks.</p>