居中的布局 view 1 view 2 view 2 居左的布局 view 1 view 2 view 2 居右的布局 view 1 view 2 view 2 两端对齐，项目之间的间隔都相等 view 1 view 2 view 2 每个项目两侧的间隔相等 view 1 view 2 view 2