sheets

You always wanted to have that card-like controller similar to that in Maps or Shortcuts, didn't you? Well, now you can have it for free with sheets! sheets provides an easy to use container controller, that has API similar to that of UINavigationController.

Installation

Swift Package Manager

Requires XCode 11. In project menu under Swift Packages add sheets via URL.

Cocoapods

In your Podfile add

pod sheets

Usage

The idea behind sheets is simple. sheets provides SheetController container view controller. It contains one main view controller and one or more view controllers, presented inside the sheet. Main view controller is what is behind the sheet. This controller cannot be changed after initialization (at least for now). View controllers inside the sheet are dynamic, meaning they can be pushed and popped as needed, though there always has to be at least one VC in the stack (having no view controllers inside the card doesn't really make that much sense).

To start using sheets in your project, initialize SheetController via init(mainViewController:rootViewController:anchors:) initializer, then present it as you would any other view controller.

Scrolling behavior

To enable the user to drag the sheet by its content, SheetController has to become a delegate of UIScrollView. Unfortunately, it is straight up impossible to set the delegate property of some scroll views (e.g. UITableView has to be its own delegate). Furthermore, various users of scroll views' API may want to intercept scrolling callbacks themselves.

To alleviate this problem sheets introduces Scrollable and ScrollableDelegate protocols. If you want your custom views to be properly scrollable when presented as a part of SheetController you'll have to route scrolling events to the delegate object.

Steps:

1. Conform your view/view controller to Scrollable protocol.
2. Call scrollableWillBeginDragging(_), scrollableDidScroll(_) and scrollableWillEndDragging(_:withVelocity:targetContentOffset:) methods inside scrollViewWillBeginDragging(_:), scrollViewDidScroll(_:) and scrollViewWillEndDragging(_:withVelocity:targetContentOffset:) respectively.

For those who do not need to override UIScrollView methods listed above sheets provides two convenience view controllers: ScrollableTableViewController and ScrollableCollectionViewController. Those VCs are Scrollable from the get-go!

Customization

Options

SheetController can be customized via a number of convenient options. Those options include:

Anchors

Another point of customization is anchors. Anchors define heights, to which sheet automatically snaps when the user stops dragging. Anchors themselves are defined in Anchor enum. Its cases are:

Anchors can be set during initialization or via setAnchors(_:animated:snapTo:) method.

Notes:

• Heights derived from anchors are computed relative to the view's safe area, so you don't have to worry about navigation bars, tab bars and toolbars.
• You don't have to order anchors in any particular way.
• The default anchors for each SheetController are defaultExpanded and defaultCollapsed.
• The exact constants for defaultExpanded and defaultCollapsed anchors are 20 points from top and 44 points from bottom respectively. The former constant replicates the expanded state of sheet-like UI in Apple's Shortcuts app. The latter constant is nice for a number of reasons: it's just enough to let the user drag on it, and when a navigation controller is presented inside thу sheet, navigation bar just barely touches the bottom in collapsed state.

App Store Presentation Style

sheets now also provides a presentation style that tries to emulate news presentation popping from below, just like Apple Arcade's categories. See AppStoreTransitioningDelegate.swift for implementation details or ExampleThreeCoordinator.swift for usage examples.

Features

AppStoreTransitioningDelegate presents view controllers by popping them from below while blurring the background. It also adds a close button that does not interfere with your view controller's view hirerachy or layout.

AppStoreTransitioningDelegate makes use of Scrollable protocol to allow for interactive dismissal through dragging down. Dismissal through left screen edge pan works for all view controllers regardless of Scrollable conformance.

Example usage

class CustomPresentingViewController: UIViewController {
	
	private let transitioningDelegate = AppStoreTransitioningDelegate()
	
	func present(this viewController: UIViewController) {
		viewController.modalPresentationStyle = .custom
		viewController.transitioningDelegate = transitioningDelegate
		present(viewController, animated: true)
	}
	
}

Note: Don't forget to retain the transitioning delegate or else this won't work.

How it looks in action

During the interactive portion of dismissal the view controller just shrinks around its center. When a certain threshold is passed, the view controller is sent downwards and completely dismissed.

Notice how during dismissal animation close button dims and its view's corner radius increases, while backround gradually loses its blur.

Examples

You can find sample use cases in this example app.

References

This library was inspired by these articles from the Yandex.Maps iOS team:

1. Custom paging in iOS
2. Drawable card UI

Licensing

This library is distributed under the MIT license.