Nowadays, an alert is merely a simple presented view controller. You can write a presented view controller that behaves similarly to an alert — that is, it pops onto the screen and dims whatever is behind it — but it's _your_ view controller and you are free to give it any interface you like.
To get you started, I've written a [github project](
[To see links please register here]
) that you can download and run, and modify to suit your actual needs.
I'll show the key part of the code. The "alert" view controller, in its initializers, sets its own modal presentation style as `custom` and sets a transitioning delegate:
```
class CustomAlertViewController : UIViewController {
let transitioner = CAVTransitioner()
override init(nibName: String?, bundle: Bundle?) {
super.init(nibName: nibName, bundle: bundle)
self.modalPresentationStyle = .custom
self.transitioningDelegate = self.transitioner
}
convenience init() {
self.init(nibName:nil, bundle:nil)
}
required init?(coder: NSCoder) {
fatalError("NSCoding not supported")
}
}
```
All the work is done by the transitioning delegate:
```
class CAVTransitioner : NSObject, UIViewControllerTransitioningDelegate {
func presentationController(
forPresented presented: UIViewController,
presenting: UIViewController?,
source: UIViewController)
-> UIPresentationController? {
return MyPresentationController(
presentedViewController: presented, presenting: presenting)
}
}
class MyPresentationController : UIPresentationController {
func decorateView(_ v:UIView) {
// iOS 8 doesn't have this
// v.layer.borderColor = UIColor.blue.cgColor
// v.layer.borderWidth = 2
v.layer.cornerRadius = 8
let m1 = UIInterpolatingMotionEffect(
keyPath:"center.x", type:.tiltAlongHorizontalAxis)
m1.maximumRelativeValue = 10.0
m1.minimumRelativeValue = -10.0
let m2 = UIInterpolatingMotionEffect(
keyPath:"center.y", type:.tiltAlongVerticalAxis)
m2.maximumRelativeValue = 10.0
m2.minimumRelativeValue = -10.0
let g = UIMotionEffectGroup()
g.motionEffects = [m1,m2]
v.addMotionEffect(g)
}
override func presentationTransitionWillBegin() {
self.decorateView(self.presentedView!)
let vc = self.presentingViewController
let v = vc.view!
let con = self.containerView!
let shadow = UIView(frame:con.bounds)
shadow.backgroundColor = UIColor(white:0, alpha:0.4)
shadow.alpha = 0
con.insertSubview(shadow, at: 0)
shadow.autoresizingMask = [.flexibleWidth, .flexibleHeight]
let tc = vc.transitionCoordinator!
tc.animate(alongsideTransition: { _ in
shadow.alpha = 1
}) { _ in
v.tintAdjustmentMode = .dimmed
}
}
override func dismissalTransitionWillBegin() {
let vc = self.presentingViewController
let v = vc.view!
let con = self.containerView!
let shadow = con.subviews[0]
let tc = vc.transitionCoordinator!
tc.animate(alongsideTransition: { _ in
shadow.alpha = 0
}) { _ in
v.tintAdjustmentMode = .automatic
}
}
override var frameOfPresentedViewInContainerView : CGRect {
// we want to center the presented view at its "native" size
// I can think of a lot of ways to do this,
// but here we just assume that it *is* its native size
let v = self.presentedView!
let con = self.containerView!
v.center = CGPoint(x: con.bounds.midX, y: con.bounds.midY)
return v.frame.integral
}
override func containerViewWillLayoutSubviews() {
// deal with future rotation
// again, I can think of more than one approach
let v = self.presentedView!
v.autoresizingMask = [
.flexibleTopMargin, .flexibleBottomMargin,
.flexibleLeftMargin, .flexibleRightMargin
]
v.translatesAutoresizingMaskIntoConstraints = true
}
}
extension CAVTransitioner { // UIViewControllerTransitioningDelegate
func animationController(
forPresented presented:UIViewController,
presenting: UIViewController,
source: UIViewController)
-> UIViewControllerAnimatedTransitioning? {
return self
}
func animationController(
forDismissed dismissed: UIViewController)
-> UIViewControllerAnimatedTransitioning? {
return self
}
}
extension CAVTransitioner : UIViewControllerAnimatedTransitioning {
func transitionDuration(
using transitionContext: UIViewControllerContextTransitioning?)
-> TimeInterval {
return 0.25
}
func animateTransition(
using transitionContext: UIViewControllerContextTransitioning) {
let con = transitionContext.containerView
let v1 = transitionContext.view(forKey: .from)
let v2 = transitionContext.view(forKey: .to)
// we are using the same object (self) as animation controller
// for both presentation and dismissal
// so we have to distinguish the two cases
if let v2 = v2 { // presenting
con.addSubview(v2)
let scale = CGAffineTransform(scaleX: 1.6, y: 1.6)
v2.transform = scale
v2.alpha = 0
UIView.animate(withDuration: 0.25, animations: {
v2.alpha = 1
v2.transform = .identity
}) { _ in
transitionContext.completeTransition(true)
}
} else if let v1 = v1 { // dismissing
UIView.animate(withDuration: 0.25, animations: {
v1.alpha = 0
}) { _ in
transitionContext.completeTransition(true)
}
}
}
}
```
It looks like a lot of code, and I suppose it is, but it's almost entire confined to a single class, which is entirely boilerplate; just copy and paste. All _you_ have to do is write the internal interface and behavior of your "alert" view controller, giving it buttons and text and whatever else you want, just as you would do for any other view controller.
]
