如何在android xml布局中将3个按钮放入3行？

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?Im trying to make a tic-tac-toe game(android ve