1Android: gravity sets the content alignment in the control. android: layout_gravity sets the alignment of the control.
2When android: gravity and android: padding are used at the same time, la s by gravity and then adjusts By padding.
3Android: padding specifies the padding (describe the problem from the perspective of the parent view, which specifies the distance between the content in it and the parent view). android: layout_margin specifies the margin (describe the problem from the perspective of the user, and specify the distance between the user and other views (up and down). If there is only one view at the same level, the effect is basically the same as that of padding)