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UIScrollView

A view that allows the scrolling and zooming of its contained views.

Declaration

@MainActor class UIScrollView

Mentioned in

Overview

UIScrollView is the superclass of several UIKit classes, including UITableView and UITextView.

A scroll view is a view with an origin that’s adjustable over the content view. It clips the content to its frame, which generally (but not necessarily) coincides with that of the app’s main window. A scroll view tracks the movements of fingers, and adjusts the origin accordingly. The view that shows its content through the scroll view draws that portion of itself according to the new origin, which is pinned to an offset in the content view. The scroll view itself does no drawing except for displaying vertical and horizontal scroll indicators. The scroll view must know the size of the content view so it knows when to stop scrolling. By default, it bounces back when scrolling exceeds the bounds of the content.

The object that manages the drawing of content that displays in a scroll view needs to tile the content’s subviews so that no view exceeds the size of the screen. As users scroll in the scroll view, this object adds and removes subviews as necessary.

Because a scroll view has no scroll bars, it must know whether a touch signals an intent to scroll versus an intent to track a subview in the content. To make this determination, it temporarily intercepts a touch-down event by starting a timer and, before the timer fires, seeing if the touching finger makes any movement. If the timer fires without a significant change in position, the scroll view sends tracking events to the touched subview of the content view. If the user then drags their finger far enough before the timer elapses, the scroll view cancels any tracking in the subview and performs the scrolling itself. Subclasses can override the touchesShouldBegin(_:with:in:), isPagingEnabled, and touchesShouldCancel(in:) methods (which the scroll view calls) to affect how the scroll view handles scrolling gestures.

A scroll view also handles zooming and panning of content. As the user makes a pinch-in or pinch-out gesture, the scroll view adjusts the offset and the scale of the content. When the gesture ends, the object managing the content view updates subviews of the content as necessary. (Note that the gesture can end and a finger might still be down.) While the gesture is in progress, the scroll view doesn’t send any tracking calls to the subview.

The UIScrollView class can have a delegate that must adopt the UIScrollViewDelegate protocol. For zooming and panning to work, the delegate must implement both viewForZooming(in:) and scrollViewDidEndZooming(_:with:atScale:). In addition, the maximumZoomScale and minimumZoomScale zoom scales must be different.

State preservation

If you assign a value to this view’s restorationIdentifier property, it attempts to preserve its scrolling-related information between app launches. Specifically, the values of the zoomScale, contentInset, and contentOffset properties are preserved. During restoration, the scroll view restores these values so that the content appears scrolled to the same position as before. For more information about how state preservation and restoration works, see App Programming Guide for iOS.

Topics

Responding to scroll view interactions

Managing the content size and offset

Managing the content inset behavior

Getting the layout guides

Configuring the scroll view

Managing the scrolling state

Applying edge effects

Managing the scroll indicator and refresh control

Scrolling to a specific location

Managing touches

Zooming and panning

Dismissing the keyboard

Managing the index

Controlling content alignment

Nesting scroll views

Deprecated

Instance Properties

See Also

Container views