参考:http://stackoverflow.com/questions/5361369/uiview-frame-bounds-and-center
UIView中有两个和位置相关的属性，一个为frame,另一个为bounds.
frame
官方文档中是这样描述frame的:
1 | The view’s frame rectangle, which defines its position and size in its superview’s coordinate system. |
意思就是frame是指view在superview的坐标系统中的position和size.
bounds
官方文档中是这样描述bounds的:
1 | The view’s bounds rectangle, which expresses its location and size in its own coordinate system. |
意思就是bounds是在自己的坐标系统中表示location和size.
center
官方文档中是这样描述center的:
1 | The center is specified within the coordinate system of its superview and is measured in points. Setting this property changes the values of the frame properties accordingly. |
center使用的是superview的坐标系统,设置center会相应的改变view的frame属性.
它们之间的关系是:
frame.origin = center - (bounds.size / 2.0)
center = frame.origin + (bounds.size / 2.0)
frame.size = bounds.size
