A UIAlertController re-implementation with controller containment support

by iOS Example

DWAlertController

When was the last time you told your designer you couldn't customize UIAlertController? Now it is possible. Without using any private API.

DWAlertController is an UIAlertController that supports displaying any view controller instead of title and message. DWAlertController fully copies the look and feel of UIAlertController and has the same API.

This alert successfully used in production in our app Dash Wallet.

Supported Features

  • iPhone / iPad compatible
  • Device rotations
  • Keyboard support
  • Customizable action buttons (normal / disabled / destructive tint colors)
  • Tap and slide over the action buttons
  • Custom presentation and dismissal transitions (corresponds to UIAlertController ones)
  • Dimming tintColor-ed views behind the alert
  • Simple built-in transition from one content controller to another within a single DWAlertController (see Advanced alert in the Example app)
  • Dynamic Type
  • Accessibility
  • Dark Mode and dark appearance for iOS 12 or lower

Usage

DWAlertController is written in Objective-C and optimized for Swift. All API that DWAlertController provides is the same as UIAlertController.

Swift

let controller = ... // instantiate view controller

let alert = DWAlertController(contentController: controller)

let okAction = DWAlertAction(title: NSLocalizedString("OK", comment: ""),
                             style: .cancel,
                             handler: nil)
alert.addAction(okAction)

present(alert, animated: true)

Objective-C

UIViewController *controller = ...; // instantiate view controller

DWAlertController *alert = [DWAlertController alertControllerWithContentController:controller];

DWAlertAction *okAction = [DWAlertAction actionWithTitle:NSLocalizedString(@"OK", nil)
                                                   style:DWAlertActionStyleCancel
                                                 handler:nil];
[alert addAction:okAction];

[self presentViewController:alert animated:YES completion:nil];

Important notice

To make DWAlertController works with a custom content controller, the view of the content controller must correctly implement Autolayout.
You might have used the same technique when implementing dynamic-sized UITableViewCell's.
For more information see https://stackoverflow.com/a/18746930

Since DWAlertController maintain scrolling of large content controllers internally (as UIAlertController does) there is no need in placing the content of content view controller within UIScrollView.

The backgroundColor of the content controller's view should be transparent (UIColor.clear).

Limitations

  • Only UIAlertController.Style.alert is supported (since there are a lot of decent implementations of actionSheet-styled controls)
  • Updating the height of the currently displaying view controller is not supported. However, when displaying a new controller with performTransition(toContentController:animated:) method, it may have a different height.

Requirements

iOS 9 or later.

Notes

The default UIAlertController achieves such vibrant and expressive background color by using the private CoreAnimation class CABackdropLayer which is lying within another private class _UIDimmingKnockoutBackdropView with UIVisualEffectView.
This layer uses a CAFilter with "overlayBlendMode" to apply the effect to the view behind it. To get more information refer this answer.

As we wanted to use this alert in production we couldn't use any of those APIs.
There are two possible options to get decent appearance comparable to using the private API.

  1. Make a screenshot of a view behind the alert and apply CIFilter with CIOverlayBlendMode to it. This approach results in the closest appearance to UIAlertController. However, there are several reasons why this approach cannot be used. Screenshotting during presentation adds a noticeable lag, neither it can't be done after presentation which might have led to blinking the content behind the alert. It would also have to take a screenshot when the user rotates the screen wich also lead to lags.
  2. Make a "hole" in the dimming view behind the alert and allow UIVisualEffectView to do all work. As a dimming view, we use CAShapeLayer with animatable path property to dynamically modify the "hole" during rotation or keyboard animation. While this is NOT a 100% smooth solution, it works almost perfectly and looks very close to UIAlertController.

All the colors and layout constants have been carefully copied from the UIAlertController.

Example

To run the example project, clone the repo, and run pod install from the Example directory first.

Installation via CocoaPods

DWAlertController is available through CocoaPods. To install
it, simply add the following line to your Podfile:

pod 'DWAlertController'

Installation via Carthage

Carthage is a decentralized dependency manager that automates the process of adding frameworks to your Cocoa application.

You can install Carthage with Homebrew using the following command:

$ brew update
$ brew install carthage

To integrate DWAlertController into your Xcode project using Carthage, specify it in your Cartfile:

github "podkovyrin/DWAlertController"

Installation via Accio

  1. Add the following to your Package.swift:
    .package(url: "https://github.com/podkovyrin/DWAlertController.git", .upToNextMajor(from: "0.2.1")),
  2. Next, add DWAlertController to your App targets dependencies like so:
    .target(name: "App", dependencies: ["DWAlertController"]),
  3. Then run accio update.

Author

Andrew Podkovyrin, podkovyrin@gmail.com

GitHub