A region of a view that generates mouse-tracking and cursor-update events when the pointer is over that region.
SDK
- macOS 10.5+
Framework
- App
Kit
Declaration
class NSTrackingArea : NSObject
Overview
When creating a tracking-area object, you specify a rectangle (in the view’s coordinate system), an owning object, and one or more options, along with (optionally) a dictionary of data. After it’s created, you add the tracking-area object to a view using the add method. Depending on the options specified, the owner of the tracking area receives mouse, mouse, mouse, and cursor messages when the mouse cursor enters, moves within, and leaves the tracking area. Currently the tracking area is restricted to rectangles.
An NSTracking object belongs to its view rather than to its window. Consequently, you can add and remove tracking rectangles without needing to worry if the view has been added to a window. In addition, this design makes it possible for the AppKit to compute the geometry of tracking areas automatically when a view moves and, in some cases, when a view changes size.
Using NSTracking, you can configure the scope of activity for mouse tracking. There are four options:
The tracking area is active only when the view is first responder.
The tracking area is active when the view is in the key window.
The tracking area is active when the application is active.
The tracking area is active always (even when the application is inactive).
Other options for NSTracking objects include specifying that the tracking area should be synchronized with the visible rectangle of the view (visible) and for generating mouse and mouse: events when the mouse is dragged.
Other NSView methods related to NSTracking objects (in addition to add) include remove and update. Views can override the latter method to recompute and replace their NSTracking objects in certain situations, such as a change in the size of the visible.