Building Cocoa Applications: A Step by Step Guide

A Closer Look at the NSView Class

NSView is one of Cocoa’s most complicated classes. If you understand how it works, you can control the display of information on the computer’s screen and have it updated quickly and efficiently.

NSView Coordinate Systems

Each Cocoa NSView has its own coordinate system that can be rotated, scaled, or otherwise transformed from the coordinate system of its superview.

Each NSView also has the following two methods that describe its position in its window:

- (NSRect)frame

Returns the NSView’s frame in the coordinate system of its superview

- (NSRect)bounds

Returns the NSView’s frame (i.e., bounds) in its own coordinate system

When you change an NSView’s coordinate system, its bounds instance variable is automatically updated to reflect the change, while its frame instance variable remains the same. The NSView class provides the following methods for inspecting and changing an NSView’s coordinate system:

- (float)boundsRotation

Returns a floating-point number for the angle, in degrees, between an NSView’s coordinate system and the coordinate system of its superview.

- (float)frameRotation

Returns the angle of the NSView’s frame relative to its superview’s coordinate system. A value of 0 means that the NSView has not been rotated (but its coordinate system may have been).

- (BOOL)isRotatedFromBase

Returns TRUE if an NSView or any of its ancestors have been rotated from the window coordinate system.

- (BOOL)isRotatedOrScaledFromBase

Returns TRUE ...