Class

UIResponder

An abstract interface for responding to and handling events.

Declaration

@interface UIResponder : NSObject

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:withEvent:, touchesMoved:withEvent:, touchesEnded:withEvent:, and touchesCancelled:withEvent: 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

nextResponder

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

isFirstResponder

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

canBecomeFirstResponder

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

becomeFirstResponder

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

canResignFirstResponder

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

resignFirstResponder

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

Responding to Touch Events

touchesBegan:withEvent:

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

touchesMoved:withEvent:

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

touchesEnded:withEvent:

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

touchesCancelled:withEvent:

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

touchesEstimatedPropertiesUpdated:

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

Responding to Motion Events

motionBegan:withEvent:

Tells the receiver that a motion event has begun.

motionEnded:withEvent:

Tells the receiver that a motion event has ended.

motionCancelled:withEvent:

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.

pressesBegan:withEvent:

Tells this object when a physical button is first pressed.

pressesChanged:withEvent:

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

pressesEnded:withEvent:

Tells the object when a button is released.

pressesCancelled:withEvent:

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

Responding to Remote-Control Events

remoteControlReceivedWithEvent:

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

Managing Input Views

inputView

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

inputViewController

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

inputAccessoryView

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

inputAccessoryViewController

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

reloadInputViews

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

Getting the Undo Manager

undoManager

Returns the nearest shared undo manager in the responder chain.

Validating Commands

canPerformAction:withSender:

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

targetForAction:withSender:

Returns the target object that responds to an action.

Accessing the Available Key Commands

keyCommands

The key commands that trigger actions on this responder.

Managing the Text Input Mode

textInputMode

The text input mode for this responder object.

textInputContextIdentifier

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

clearTextInputContextIdentifier:

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

inputAssistantItem

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

Supporting User Activities

userActivity

An object encapsulating a user activity supported by this responder.

restoreUserActivityState:

Restores the state needed to continue the given user activity.

updateUserActivityState:

Updates the state of the given user activity.

Relationships

Inherits From

See Also

First Steps

Using Responders and the Responder Chain to Handle Events

Learn how to handle events that propagate through your app.

UIEvent

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