UIView is a class in the UIKit framework of iOS defines a rectangular area on the screen and the interfaces for managing the content in that area. All UI elements are either subclasses of UIView or are contained within a UIView.
The UIView class defines a rectangular area on the screen and the interfaces for managing the content in that area. At runtime, a view object handles the rendering of any content in its area and also handles any interactions with that content. The UIView class itself provides basic behavior for filling its rectangular area with a background color. More sophisticated content can be presented by subclassing UIView and implementing the necessary drawing and event-handling code yourself. The UIKit framework also includes a set of standard subclasses that range from simple buttons to complex tables and can be used as-is. For example, a UILabel object draws a text string and a UIImageView object draws an image.
Because view objects are the main way your application interacts with the user, they have a number of responsibilities. Here are just a few:
Drawing and animation
Views draw content in their rectangular area using technologies such as UIKit, Core Graphics, and OpenGL ES.
Some view properties can be animated to new values.
Layout and subview management
A view may contain zero or more subviews.
Each view defines its own default resizing behavior in relation to its parent view.
A view can define the size and position of its subviews as needed.
Event handling
- A view is a responder and can handle touch events and other events defined by the UIResponder class.
- Views can use the addGestureRecognizer: method to install gesture recognizers to handle common gestures.
Views can embed other views and create sophisticated visual hierarchies. This creates a parent-child relationship between the view being embedded (known as the subview) and the parent view doing the embedding (known as the superview). Normally, a subview’s visible area is not clipped to the bounds of its superview, but in iOS you can use the clipsToBounds property to alter that behavior. A parent view may contain any number of subviews but each subview has only one superview, which is responsible for positioning its subviews appropriately.
The geometry of a view is defined by its frame, bounds, and center properties. The frame defines the origin and dimensions of the view in the coordinate system of its superview and is commonly used during layout to adjust the size or position of the view. The center property can be used to adjust the position of the view without changing its size. The bounds defines the internal dimensions of the view as it sees them and is used almost exclusively in custom drawing code. The size portion of the frame and bounds rectangles are coupled together so that changing the size of either rectangle updates the size of both.
For detailed information about how to use the UIView class, see View Programming Guide for iOS.
Creating a View
To create a view programmatically, you can use code like the following:
CGRect viewRect = CGRectMake(10, 10, 100, 100);
UIView* myView = [[UIView alloc] initWithFrame:viewRect];
Equivalent in Swift is:
let viewRect = CGRectMake(10, 10, 100, 100)
let myView = UIView(frame: viewRect)
