Look Who it Was Random video

Introduction to Gesture Recognizers - Gesture Recognizers in IOS 12, Xcode 10, and Swift 4.2

1,234 views · Published 3 December 2018 · 1:51 · Indexed 24 October 2026

Channel: Kodeco · 2018 · Education

Watch on YouTube

Learn a bit of the history of gesture recognizers in iOS, and what we will be covering in this course.

About the Course:

Touch interaction is a fundamental component of iOS and UIGestureRecognizer is the key to easy-to-use gestures beyond simple button taps. Learn about it here!

View the playlist:

https://www.youtube.com/playlist?list=PL23Revp-82LISd6lntATAhnk4pEmo3AGY

View episode:

https://www.raywenderlich.com/9225-gesture-recognizers-in-ios/lessons/1

---

About www.raywenderlich.com:

raywenderlich.com is a website focused on developing high quality programming tutorials. Our goal is to take the coolest and most challenging topics and make them easy for everyone to learn – so we can all make amazing apps.

We are also focused on developing a strong community. Our goal is to help each other reach our dreams through friendship and cooperation. As you can see below, a bunch of us have joined forces to make this happen: authors, editors, subject matter experts, app reviewers, and most importantly our amazing readers!

---

A gesture-recognizer object—or, simply, a gesture recognizer—decouples the logic for recognizing a sequence of touches (or other input) and acting on that recognition. When one of these objects recognizes a common gesture or, in some cases, a change in the gesture, it sends an action message to each designated target object.

The UIGestureRecognizer class defines a set of common behaviors that can be configured for all concrete gesture recognizers. It can also communicate with its delegate (an object that adopts the UIGestureRecognizerDelegate protocol), thereby enabling finer-grained customization of some behaviors.

A gesture recognizer operates on touches hit-tested to a specific view and all of that view’s subviews. It thus must be associated with that view. To make that association you must call the UIView method addGestureRecognizer(_:). A gesture recognizer doesn’t participate in the view’s responder chain.

A gesture recognizer has one or more target-action pairs associated with it. If there are multiple target-action pairs, they are discrete, and not cumulative. Recognition of a gesture results in the dispatch of an action message to a target for each of the associated pairs.

Methods conforming to the latter signature permit the target in some cases to query the gesture recognizer sending the message for additional information. For example, the target could ask a UIRotationGestureRecognizer object for the angle of rotation (in radians) since the last invocation of the action method for this gesture. Clients of gesture recognizers can also ask for the location of a gesture by calling location(in:) or location(ofTouch:in:).

The gesture interpreted by a gesture recognizer can be either discrete or continuous. A discrete gesture, such as a double tap, occurs but once in a multi-touch sequence and results in a single action sent. However, when a gesture recognizer interprets a continuous gesture such as a rotation gesture, it sends an action message for each incremental change until the multi-touch sequence concludes.

A window delivers touch events to a gesture recognizer before it delivers them to the hit-tested view attached to the gesture recognizer. Generally, if a gesture recognizer analyzes the stream of touches in a multi-touch sequence and doesn’t recognize its gesture, the view receives the full complement of touches. If a gesture recognizer recognizes its gesture, the remaining touches for the view are cancelled. The usual sequence of actions in gesture recognition follows a path determined by default values of the cancelsTouchesInView, delaysTouchesBegan, delaysTouchesEnded properties:

cancelsTouchesInView—If a gesture recognizer recognizes its gesture, it unbinds the remaining touches of that gesture from their view (so the window won’t deliver them). The window cancels the previously delivered touches with a (touchesCancelled(_:with:)) message. If a gesture recognizer doesn’t recognize its gesture, the view receives all touches in the multi-touch sequence.

delaysTouchesBegan—As long as a gesture recognizer, when analyzing touch events, has not failed recognition of its gesture, the window withholds delivery of touch objects in the UITouch.Phase.began phase to the attached view. If the gesture recognizer subsequently recognizes its gesture, the view doesn’t receive these touch objects. If the gesture recognizer doesn’t recognize its gesture, the window delivers these objects in an invocation of the view’s touchesBegan(_:with:) method (and possibly a follow-up touchesMoved(_:with:) invocation to inform it of the touches current location).

delaysTouchesEnded—As long as a gesture recognizer, when analyzing touch events, has not failed recognition of its gesture, the window withholds delivery of touch objects in the UITouch.Phase.ended phase to the attached view.

More from this channel