UIView s frame bounds center origin when to use what

Question

UIView has the properties frame  bounds  center  and origin  and they all seem to be interrelated   Most of the time  I deal with frame when setting the position and size of a UIView   I understand that frame is using global coordinate system and bounds is using coordinate of the local view  therefore its x and y are 0  but not always   but it s still confusing to me when to use what   Under what context  and what s the right time  the other properties  bounds  center  origin  should be used

User · Answer

The properties center  bounds and frame are interlocked  changing one will update the others  so use them however you want  For example  instead of modifying the x y params of frame to recenter a view  just update the center property

User · Answer

They are related values  and kept consistent by the property setter getter methods  and using the fact that frame is a purely synthesized value  not backed by an actual instance variable    The main equations are   frame origin   center - bounds size   2    which is the same as   center   frame origin   bounds size   2    and there   s also   frame size   bounds size   That s not code  just equations to express the invariant between the three properties   These equations also assume your view s transform is the identity  which it is by default   If it s not  then bounds and center keep the same meaning  but frame can change   Unless you re doing non-right-angle rotations  the frame will always be the transformed view in terms of the superview s coordinates   This stuff is all explained in more detail with a useful mini-library here   http   bynomial com blog  p 24

User · Answer

Marco s answer above is correct  but just to expand on the question of  under what context      frame - this is the property you most often use for normal iPhone applications   most controls will be laid out relative to the  containing  control so the frame origin will directly correspond to where the control needs to display  and frame size will determine how big to make the control     center - this is the property you will likely focus on for sprite based games and animations where movement or scaling may occur   By default animation and rotation will be based on the center of the UIView   It rarely makes sense to try and manage such objects by the frame property   bounds - this property is not a positioning property  but defines the drawable area of the UIView  relative  to the frame   By default this property is usually  0  0  width  height    Changing this property will allow you to draw outside of the frame or restrict drawing to a smaller area within the frame   A good discussion of this can be found at the link below   It is uncommon for this property to be manipulated unless there is specific need to adjust the drawing region   The only exception is that most programs will use the   UIScreen mainScreen  bounds  on startup to determine the visible area for the application and setup their initial UIView s frame accordingly   Why is there an frame rectangle and an bounds rectangle in an UIView   Hopefully this helps clarify the circumstances where each property might get used

[uiview] UIView's frame, bounds, center, origin, when to use what?

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