touchUpInside

TouchUpInside is a UIControl event in Apple's UIKit framework. It is triggered when a user taps a UIControl subclass, such as a UIButton, and lifts the finger while the touch remains inside the control’s bounds. This event is commonly used to respond to a primary tap action.

Behavior and scope

TouchUpInside fires after a touch begins inside the control and ends inside the control, ensuring the user completed a deliberate tap. It does not fire if the touch ends outside the control, if the finger moves outside before lifting, or if the system cancels the touch. It is one of several UIControl events and is typically preferred for button-like interactions because it matches user intent.

Usage

Developers attach actions to this event via target-action mechanisms. In Swift, a common pattern is:

button.addTarget(self, action: #selector(handleTap(_:)), for: .touchUpInside)

In Objective-C, the equivalent is:

[button addTarget:self action:@selector(handleTap:) forControlEvents:UIControlEventTouchUpInside];

This event can be used with various UIControls beyond UIButton, including other tappable controls that inherit from UIControl.

Design considerations

TouchUpInside is generally the recommended event for responding to button presses because it requires the user to complete a tap within the control. Developers may contrast it with events like touchDown (fires when the finger first touches the control) or touchUpOutside (fires if the finger is released outside the control) to support different interaction patterns.

Accessibility

For accessibility users, the action associated with touchUpInside is typically exposed as the control’s primary action, aligning with standard assistive interaction expectations.