Do I have the right understanding of frames and bounds in UIKit?

Question

Let me try to explain it. Please tell me if I am wrong. I am just 70% sure about it.

Like I understand it, an UIView has a frame and an bounds rectangle. The job of the frame rectangle is to set the position of the UIView relative to it's superview. More precisely: Relative to the coordinate system of the superview. The job of the bounds rectangle is to set the drawing area of the UIView, relative to it's own coordinate system.

Briefly:

• frame rectangle is for positioning the UIView relative to its superview
• bounds rectangle is to set the drawing area of the UIView

Are there any mistakes or important things I missed?

Answer 1

Yes you are right.

When you need to use the view, then you use the frame; the bounds are used to actually implement the view. As an example, you need to use the bounds to draw a view or to handle touch events. Instead, you use the frame when creating a view or positioning a view in its superview etc.

Answer 2

You are right.

You can use the two interchangably though it's just the frame is easier when using a view and bounds is easier when working inside a view (e.g. in the event handling or drawing code)

Note also that frame is undefined if there is a transform operating on the view.

Answer 3

Check out Apple's guide on View Geometry. They have pretty good examples on what happens when you change bounds and frame values.

Answer 4

A view's Frame: the position and size of a rectangle inside the superview where the view will fill.

A view's Bound: the position and size of a rectangle inside the view itself.