Ray's playground

摘要：UIViewController has several methods that get called at certain times: viewWillAppear: when its view is about to be added to the window viewDidAppear: when its view has been added to the window viewWillDisappear: when its view is about to be dismissed, covered, or otherwisehidden from view viewDidDi 阅读全文

摘要：Every UIView subclass implements the method drawRect:, which contains the drawing code for theview. For example, a UIButton’s drawRect: method draws a rounded rectangle with a title string in thecenter. Each time an instance of UIView needs to be drawn (or redrawn), the system prepares a graphicsco. 阅读全文

摘要：The Core Location framework tells us where we are in the world; the MapKit framework shows usthat world. Most of MapKit’s work is done by the class MKMapView. Instances of this type display amap, track touches, and display annotations. 阅读全文

摘要：Delegation is an object-oriented approach to callbacks. A callback is a function that is supplied inadvance of an event and is called every time the event occurs. Some objects need to make a callbackfor more than one event. For instance, the location manager wants to “callback” when it finds a newl. 阅读全文