UGUI Make Use Of Grid Layout Group

1.Buttons

Grid layout Group,Set group of Buttons vertical by one column,

but The Size is hard to arrange.So

1>Create new GameObject in canvas with component of rect transform and Grid layout Group.

2>Then Create several Buttons under the Gameobject
3>scale the gameobject smaller to available size 
4>then turn off the component Grid layout Group,then arrange the rect transform to adapt to the shape of Grid group of buttons,center to it's center.
5>move the gameobject to the available position
6>then put the component Grid layout Group of the GameObject 

to the target panel.

7>Arrange the anchors of each button to adapt to the target rect transform.