Class

UIResponder

An abstract interface for responding to and handling events.

Overview

Responder objects—that is, instances of UIResponder—constitute the event-handling backbone of a UIKit app. Many key objects are also responders, including the UIApplication object, UIViewController objects, and all UIView objects (which includes UIWindow). As events occur, UIKit dispatches them to your app's responder objects for handling.

There are several kinds of events, including touch events, motion events, remote-control events, and press events. To handle a specific type of event, a responder must override the corresponding methods. For example, to handle touch events, a responder implements the touchesBegan(_:with:), touchesMoved(_:with:), touchesEnded(_:with:), and touchesCancelled(_:with:) methods. In the case of touches, the responder uses the event information provided by UIKit to track changes to those touches and to update the app's interface appropriately.

In addition to handling events, UIKit responders also manage the forwarding of unhandled events to other parts of your app. If a given responder does not handle an event, it forwards that event to the next event in the responder chain. UIKit manages the responder chain dynamically, using predefined rules to determine which object should be next to receive an event. For example, a view forwards events to its superview, and the root view of a hierarchy forwards events to its view controller.

Responders process UIEvent objects but can also accept custom input through an input view. The system's keyboard is the most obvious example of an input view. When the user taps a UITextField and UITextView object onscreen, the view becomes the first responder and displays its input view, which is the system keyboard. Similarly, you can create custom input views and display them when other responders become active. To associate a custom input view with a responder, assign that view to the inputView property of the responder.

For information about responders and the responder chain, see Event Handling Guide for UIKit Apps.

Topics

Managing the Responder Chain

var next: UIResponder?

Returns the next responder in the responder chain, or nil if there is no next responder.

var isFirstResponder: Bool

Returns a Boolean value indicating whether this object is the first responder.

var canBecomeFirstResponder: Bool

Returns a Boolean value indicating whether this object can become the first responder.

func becomeFirstResponder() -> Bool

Asks UIKit to make this object the first responder in its window.

var canResignFirstResponder: Bool

Returns a Boolean value indicating whether the receiver is willing to relinquish first-responder status.

func resignFirstResponder() -> Bool

Notifies this object that it has been asked to relinquish its status as first responder in its window.

Responding to Touch Events

func touchesBegan(Set<UITouch>, with: UIEvent?)

Tells this object that one or more new touches occurred in a view or window.

func touchesMoved(Set<UITouch>, with: UIEvent?)

Tells the responder when one or more touches associated with an event changed.

func touchesEnded(Set<UITouch>, with: UIEvent?)

Tells the responder when one or more fingers are raised from a view or window.

func touchesCancelled(Set<UITouch>, with: UIEvent?)

Tells the responder when a system event (such as a system alert) cancels a touch sequence.

func touchesEstimatedPropertiesUpdated(Set<UITouch>)

Tells the responder that updated values were received for previously estimated properties or that an update is no longer expected.

Responding to Motion Events

func motionBegan(UIEvent.EventSubtype, with: UIEvent?)

Tells the receiver that a motion event has begun.

func motionEnded(UIEvent.EventSubtype, with: UIEvent?)

Tells the receiver that a motion event has ended.

func motionCancelled(UIEvent.EventSubtype, with: UIEvent?)

Tells the receiver that a motion event has been cancelled.

Responding to Press Events

Generally, responders that handle press events should override all four of these methods.

func pressesBegan(Set<UIPress>, with: UIPressesEvent?)

Tells this object when a physical button is first pressed.

func pressesChanged(Set<UIPress>, with: UIPressesEvent?)

Tells this object when a value associated with a press has changed.

func pressesEnded(Set<UIPress>, with: UIPressesEvent?)

Tells the object when a button is released.

func pressesCancelled(Set<UIPress>, with: UIPressesEvent?)

Tells this object when a system event (such as a low-memory warning) cancels a press event.

Responding to Remote-Control Events

func remoteControlReceived(with: UIEvent?)

Tells the object when a remote-control event is received.

Managing Input Views

var inputView: UIView?

The custom input view to display when the receiver becomes the first responder.

var inputViewController: UIInputViewController?

The custom input view controller to use when the receiver becomes the first responder.

var inputAccessoryView: UIView?

The custom input accessory view to display when the receiver becomes the first responder.

var inputAccessoryViewController: UIInputViewController?

The custom input accessory view controller to display when the receiver becomes the first responder.

func reloadInputViews()

Updates the custom input and accessory views when the object is the first responder.

Getting the Undo Manager

var undoManager: UndoManager?

Returns the nearest shared undo manager in the responder chain.

Validating Commands

func canPerformAction(Selector, withSender: Any?) -> Bool

Requests the receiving responder to enable or disable the specified command in the user interface.

func target(forAction: Selector, withSender: Any?) -> Any?

Returns the target object that responds to an action.

Accessing the Available Key Commands

var keyCommands: [UIKeyCommand]?

The key commands that trigger actions on this responder.

Managing the Text Input Mode

var textInputMode: UITextInputMode?

The text input mode for this responder object.

var textInputContextIdentifier: String?

An identifier signifying that the responder should preserve its text input mode information.

class func clearTextInputContextIdentifier(String)

Clears text input mode information from the app’s user defaults.

var inputAssistantItem: UITextInputAssistantItem

The input assistant to use when configuring the keyboard’s shortcuts bar.

Supporting User Activities

var userActivity: NSUserActivity?

An object encapsulating a user activity supported by this responder.

func restoreUserActivityState(NSUserActivity)

Restores the state needed to continue the given user activity.

func updateUserActivityState(NSUserActivity)

Updates the state of the given user activity.

Type Properties

class let keyboardAnimationCurveUserInfoKey: String

The key for an NSNumber object containing a UIView.AnimationCurve constant that defines how the keyboard will be animated onto or off the screen.

class let keyboardAnimationDurationUserInfoKey: String

The key for an NSNumber object containing a double that identifies the duration of the animation in seconds.

class let keyboardDidChangeFrameNotification: NSNotification.Name

Posted immediately after a change in the keyboard’s frame.

class let keyboardDidHideNotification: NSNotification.Name

Posted immediately after the dismissal of the keyboard.

class let keyboardDidShowNotification: NSNotification.Name

Posted immediately after the display of the keyboard.

class let keyboardFrameBeginUserInfoKey: String

The key for an NSValue object containing a CGRect that identifies the starting frame rectangle of the keyboard in screen coordinates. The frame rectangle reflects the current orientation of the device.

class let keyboardFrameEndUserInfoKey: String

The key for an NSValue object containing a CGRect that identifies the ending frame rectangle of the keyboard in screen coordinates. The frame rectangle reflects the current orientation of the device.

class let keyboardIsLocalUserInfoKey: String

The key for an NSNumber object containing a Boolean that identifies whether the keyboard belongs to the current app. With multitasking on iPad, all visible apps are notified when the keyboard appears and disappears. The value of this key is true for the app that caused the keyboard to appear and false for any other apps.

class let keyboardWillChangeFrameNotification: NSNotification.Name

Posted immediately prior to a change in the keyboard’s frame.

class let keyboardWillHideNotification: NSNotification.Name

Posted immediately prior to the dismissal of the keyboard.

class let keyboardWillShowNotification: NSNotification.Name

Posted immediately prior to the display of the keyboard.

See Also

First Steps

Using Responders and the Responder Chain to Handle Events

Learn how to handle events that propagate through your app.

class UIEvent

An object that describes a single user interaction with your app.