Playground showing how to use swift2 protocol extensions to render errors in UIViews and UIViewControllers without subclassing
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Swift2-ProtocolExtensions-ErrorRendering.playground
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README.md
example.gif
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README.md

Swift 2.0 Protocol Extension Example

Playground showing how to use Swift2 protocol extensions to render errors in UIViews and UIViewControllers without subclassing or creating classes

UIViewControllers will render an error as a toast banner

UIViews will render an error by adding a generic error label to the views top right corner.

This was inspired by a sweet article by KrakenDev

import UIKit
import XCPlayground

struct ErrorOptions {
    let message: String
    let tintColor: UIColor
    
    init(message: String = "Error!", tintColor: UIColor = UIColor.clearColor()) {
        self.message = message
        self.tintColor = tintColor
    }
}

typealias ErrorRenderingCompletionBlock = ()->()

protocol ErrorPopoverRenderer {
    func presentError(errorOptions: ErrorOptions)
    func presentError(errorOptions: ErrorOptions, completion : ErrorRenderingCompletionBlock?)
}

extension ErrorPopoverRenderer {
    func presentError(errorOptions: ErrorOptions = ErrorOptions()) {
        self.presentError(errorOptions, completion: nil)
    }
}

extension ErrorPopoverRenderer where Self: UIViewController {

    func presentError(errorOptions: ErrorOptions = ErrorOptions(), completion : ErrorRenderingCompletionBlock?) {
        let errorBanner = UILabel()
        errorBanner.backgroundColor = errorOptions.tintColor
        errorBanner.textAlignment = .Center
        errorBanner.adjustsFontSizeToFitWidth = true
        errorBanner.font = UIFont.systemFontOfSize(20.0)
        errorBanner.textColor = UIColor.whiteColor()
        errorBanner.text = errorOptions.message
        let height : CGFloat = 50
        errorBanner.frame = CGRect(x: 0, y: -height, width: CGRectGetWidth(self.view.bounds), height: height)
        self.view.addSubview(errorBanner)
        UIView.animateWithDuration(0.8, animations: { () -> Void in
            errorBanner.transform = CGAffineTransformMakeTranslation(0, height)
            }) { (done1) -> Void in
                UIView.animateWithDuration(0.8, delay: 0.5, options: UIViewAnimationOptions.CurveEaseOut, animations: { () -> Void in
                    errorBanner.transform = CGAffineTransformIdentity
                    }, completion: { (done2) -> Void in
                        errorBanner.removeFromSuperview()
                        if let completionBlock = completion {
                            completionBlock()
                        }
                })
        }
    }
}

extension ErrorPopoverRenderer where Self: UIView {
    
    func presentError(errorOptions: ErrorOptions = ErrorOptions(), completion : ErrorRenderingCompletionBlock?) {
        let errorBanner = UILabel()
        errorBanner.backgroundColor = errorOptions.tintColor
        errorBanner.textAlignment = .Center
        errorBanner.adjustsFontSizeToFitWidth = true
        errorBanner.font = UIFont.systemFontOfSize(18.0)
        errorBanner.text = "!"
        errorBanner.textColor = UIColor.redColor()
        let size : CGFloat = 32.0
        let padding : CGFloat = 8.0
        errorBanner.layer.cornerRadius = size/2.0
        errorBanner.layer.borderColor = UIColor.redColor().CGColor
        errorBanner.layer.borderWidth = 1.0
        errorBanner.frame = CGRect(x: CGRectGetWidth(self.bounds) - size - padding, y: padding, width: size, height: size)
        self.addSubview(errorBanner)
        if let completionBlock = completion {
            completionBlock()
        }
    }
}

extension UIViewController : ErrorPopoverRenderer {}
extension UIView : ErrorPopoverRenderer {}


let viewController = UIViewController()
viewController.view.frame = CGRect(x: 0, y: 0, width: 375, height: 667)
viewController.view.backgroundColor = UIColor.whiteColor()
XCPShowView("Controller View", view: viewController.view)

let errorOptions = ErrorOptions(message: "OMG an error!", tintColor: UIColor.redColor())
viewController.presentError(errorOptions) { () -> () in
    viewController.view.presentError()
}