UICoordinate protocol defines methods for converting between different frames of reference on a screen. The
UIView class adopts this protocol so that you can convert easily between most coordinate spaces in your app. The
UIScreen class includes the
fixed properties, which give you access to the screen’s coordinate spaces. You can adopt this protocol in your own classes to convert between your custom coordinate spaces and the coordinate spaces of your app’s views and screens.
- iOS 8.0+
- tvOS 9.0+
Prior to iOS 8, window and screen coordinates were fixed and always specified relative to the device’s screen in a portrait orientation. Even when the user rotated the device, window and screen coordinates never changed because the window and screen coordinate spaces never rotated. Instead, the views installed in those windows rotated depending on whether their owning view controller supported the given device orientation. Because the window and screen coordinates never changed, apps always had a fixed frame of reference for coordinates.
In iOS 8 and later, window and screen coordinate spaces are no longer fixed to a specific device orientation. Instead, window and screen coordinates change to match the app’s interface orientation, which typically (but not always) matches the current device orientation. (View controllers still determine which interface orientations the app supports.) Rotating the window and screen simplifies the interactions between views, windows, and the screen. In cases where you still need a fixed frame of reference—for example, because you need to store the location of a touch event or onscreen item persistently—you can use the methods of this protocol to convert coordinate values to the fixed coordinate space provided by the
To convert a point from a view’s current coordinate space to the screen’s fixed coordinate space, use code similar to the following:
When implementing the methods of this protocol, you must convert coordinate values to or from your local coordinate space. When performing such conversions, use the screen coordinate space as an intermediate coordinate space, converting to screen coordinates before converting to the target coordinate space. For example, when converting from your local coordinate space to the coordinate space of another view, convert your local coordinates to the screen coordinate space first and then convert those screen coordinates to the coordinate space of the view.