UIControlState

UIControlState is a bitmask type used by UIControl and its subclasses to describe the current state of a control, such as a button. It is used by the system to determine appearance and behavior in response to user interactions. In Objective-C, UIControlState is defined as an NS_OPTIONS value, enabling multiple states to be stored in a single variable. In Swift, the equivalent is UIControl.State, an OptionSet.

States can be combined. A control may be in more than one state at once, though some combinations are more common than others (for example, a control can be both highlighted and selected). The normal state represents the default appearance when no other state is active.

Common states include:

- Normal: the default state when no other state applies.

- Highlighted: during touch-down or pressing, often used to show a pressed look.

- Disabled: when the control is not interactive, usually dimmed.

- Selected: when a control is chosen or toggled on.

- Focused: relevant on tvOS and devices with focus-based navigation.

- Application and Reserved: internal or future-use states.

Usage and behavior:

UIControlState is used by APIs that customize appearance for specific states, such as setTitle:forState:, setImage:forState:, or setTitleColor:forState:. The system updates the state automatically in response to user interactions, focus changes, or property changes. Developers can also check or combine states programmatically to implement custom logic. In Swift, you typically refer to states like .highlighted, .disabled, or [.highlighted, .selected].

Notes:

The focus state is particularly pertinent on tvOS. Application and Reserved are intended for internal use and future expansion. While UIControlState is still referenced in Objective-C, Swift code uses UIControl.State.