if (error) { // TODO } - Speaker Deck

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if (error) { // TODO } Sven Titgemeyer 15.09.2018

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Wer bin ich? • iOS Enthusiast • Freelancer • große Projekte • Student • kleine Projekte • Open Source (iCarambaa) @s_titgemeyer

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- (void)someMethod { NSURLSession *session = [NSURLSession sharedSession]; [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { if (error) { // TODO return; } // Continue with success case. }]; }

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func someFunction() { URLSession.shared.dataTask(with: url) { (data, response, error) in guard let data = data else { // TODO return } // Continue... } }

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func someFunction() { URLSession.shared.dataTask(with: url) { (data, response, error) in guard let data = data else { print("Error: \(error!)") return } // Continue... } }

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Agenda • Error Handling Patterns • Was macht der Mac? • Error erstellen • Error weiterreichen • Error anzeigen Metal Systemframeworks Andere Frameworks Eigene Frameworks App Error Error

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UIAlertView

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UIAlertView ^(NSData *data, NSURLResponse *response, NSError *error) { if (data) { // Success case... } else { dispatch_async(dispatch_get_main_queue(), ^{ UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:error.localizedDescription delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil]; [alert show]; }); } }

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UIAlertView ✗

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UIAlertController

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UIAlertController -[UIAlertController show] ✗

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UIAlertController •Ein Alert ist ein View Controller •Wollen wir einen View Controller an x verschiedenen Stellen initialisieren? •… oder innerhalb eines Models? •Fragen wir Stackoverﬂow! •“Present UIAlertController without View Controller”

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UIAlertController

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UIAlertController • Eigene Alert über oder unter Systemalerts? • Window teilen oder kriegt jedes ein eigenes? • Mehrere Alerts übereinander? Kurz: Don’t

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macOS

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macOS @interface NSResponder(NSErrorPresentation) - (BOOL)presentError:(NSError *)error; - (NSError *)willPresentError:(NSError *)error; @end

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macOS dispatch_async(dispatch_get_main_queue(), ^{ BOOL didRecover = [self presentError:error]; if (didRecover) { // Retry. } }

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macOS

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NSError Code Domain NSLocalizedDescriptionKey NSLocalizedFailureErrorKey NSLocalizedFailureReasonErrorKey NSLocalizedRecoverySuggestionErrorKey … Beispiel: NSFileWriteOutOfSpaceError “The image library could not be saved.” “The volume Macintosh HD is out of space.” NSLocalizedRecoveryOptionsErrorKey NSRecoveryAttempterErrorKey

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Localized Description • Beschreibung aus dem Inhalt des Errors • “The image library could not be saved. The volume Macintosh HD is out of space.” • Mehrere Regeln, je nachdem, welche Informationen gesetzt sind. • Dokumentation nur in den Foundation Release Notes:   https://developer.apple.com/library/archive/releasenotes/Foundation/RN-Foundation/index.html

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Responder Chain UIResponder UIView UIApplication UIViewController

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UIView UIApplication UIViewController Superview UIViewController

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UIResponder erweitern @interface UIResponder (STIErrorPresentation) - (void)presentError:(NSError *)error completionHandler:(nullable void (^)(BOOL didRecover))completionHandler; - (nullable NSError *)willPresentError:(NSError *)error; @end

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UIApplication UIViewController UIViewController AppDelegate willPresentError: willPresentError: willPresentError: willPresentError: presentError: presentError: presentError: presentError: Achtung: Niemals [UIResponder presentError:] überschreiben

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Erneut versuchen

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@interface NSObject(NSErrorRecoveryAttempting) - (BOOL)attemptRecoveryFromError:(NSError *)error optionIndex:(NSUInteger)recoveryOptionIndex; @end

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STIRecoveryAttempter *a = [STIRecoveryAttempter new]; [a addOkayRecoveryOption]; [a addRecoveryOptionWithTitle: @"Retry" recoveryAttempt:^BOOL{ return YES; }]; NSError *_error = [error addingObject:a forUserInfoKey:NSRecoveryAttempterErrorKey]; [self presentError:_error completionHandler:^(BOOL didRecover) { if (didRecover) { [self loadFlightStatusUsingFlightnumber]; } }];

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Problem • Error Fall wird komplizierter • Duplizierter Code • Retry Option wird an jeden Error angehangen • Besser: Konﬁguriere Errors an zentraler Stelle!

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UIApplication UIViewController UIViewController AppDelegate willPresentError: willPresentError: willPresentError: willPresentError: presentError: presentError: presentError: presentError:

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UIApplication UIViewController UIViewController AppDelegate willPresentError: willPresentError: willPresentError: willPresentError:

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UIApplication UIViewController UIViewController willPresentError: willPresentError: willPresentError: STIErrorConfigurator willPresentError: STIErrorConfigurator STIErrorConfigurator NSError -domain -code

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Abfangen

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@interface UIResponder (STIErrorPresentation) - (BOOL)canInterceptError:(NSError *)error; - (void)interceptError:(NSError *)error completionHandler:(void (^)(BOOL didRecover))completionHandler; @end Error Domains nutzen

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STIErrorHandling • Open Source • Fork von HRSCustomErrorHandling • Schlank • Optimal auch für kleine Projekte • https://github.com/iCarambaa/STIErrorHandling

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Demo

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Zusammenfassung • Jeder Error der auftreten kann, tritt auch auf • Informationen aus NSError nutzen • Responder Chain kann den Fluss übernehmen • Besonders in kleinen Projekten eine einfache Lösung

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Q&A • Error erstellen • Responder Chain • Error-Präsentation • Error Conﬁgurator @s_titgemeyer • STIErrorHandling • Swift