Async View Controllers - Speaker Deck

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ASYNC VIEWCONTROLLERS Tom Adriaenssen @inferis ∴ http://inferis.org

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VIEW CONTROLLERS

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ASYNC

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ANATOMY OF ASYNC DATA 1. start slow call 2. show hey, keep yer pants on indicator 3. wait for call to finish 4. remove pants indicator 5. show your actual data

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SOME HISTORY

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MASSIVE VIEW CONTROLLER

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MASSIVE VIEW CONTROLLER IPHONE - 1.0 // Lines of code, including whitespace * Hotspot: * HSViewController .h: 25, .m: 716 * HSBoxController .h: 44, .m: 370 * Portfolio: .h: 14, .m: 523

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TECHNICAL DEBT

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BREAK THINGS UP

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INTRODUCING ASYNCVIEWCONTROLLER

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@interface AsyncViewController : UIViewController @property (nonatomic, strong, readonly) UIView *asyncView; @property (nonatomic, strong, readonly) UIView *statusView; - (void)performAsyncDataRequest; @end

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Y U NO SWIFT?

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@property (nonatomic, strong) UIView *asyncView;

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UIView *

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@Inferis None yet. You can deﬁne a generic parameter , but that isn't representable as a type yet. — @jckarter

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rdar://20990743

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rdar://20990743

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SUBCLASS OF UIViewController

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@property (nonatomic, strong, readonly) UIView *asyncView;

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@property (nonatomic, strong, readonly) UIView *statusView;

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- performAsyncDataRequest

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ASYNC DATA FETCH & STATUSVIEW + ASYNCVIEW & VIEW CONTROLLER CONTAINMENT

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SRP

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A MORE PURE MVC

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EASE OF USE

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FLEXIBLE

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TESTABLE

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@protocol IIAsyncView @required @property (nonatomic, strong, readonly) id asyncData; - (void)asyncDataApplyValueAnimated:(BOOL)animated; @optional // ... @end

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@protocol IIAsyncData @required @property (nonatomic, assign, readonly) BOOL loading; @property (nonatomic, strong) NSError *error; @property (nonatomic, strong) id value; - (void)reset; @end

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typedef NS_ENUM(NSUInteger, AsyncStatusViewState) { IIAsyncStatusLoading, IIAsyncStatusError, IIAsyncStatusNoData, IIAsyncStatusData };

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- (AsyncStatusViewState)determineState { // determine the new state if (![self isAsyncViewLoaded] || [self.asyncView.asyncData isLoading]) { return AsyncStatusLoading; } else if (self.asyncView.asyncData.error) { return AsyncStatusError; } else if (self.asyncView.asyncData.value) { return AsyncStatusData; } else { return AsyncStatusNoData; } }

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@protocol IIAsyncData @required @property (nonatomic, assign, readonly) BOOL loading; @property (nonatomic, strong) NSError *error; @property (nonatomic, strong) id value; @property (nonatomic, weak) id asyncDataDelegate; - (void)reset; - (void)invalidateState; @end @protocol IIAsyncDataDelegate @required - (void)asyncData:(id)data didInvalidateStateForced:(BOOL)forced; - (void)reloadAsyncData; @end

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@protocol AsyncView @required // ... @optional - (id)asyncNoDataMessage; - (BOOL)asyncCanReload; @end

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@protocol AsyncStatusView @required @property (nonatomic, strong) UIView *asyncView; - (void)transitionToLoadingStateAnimated:(BOOL)animated; - (void)transitionToErrorState:(NSError*)error animated:(BOOL)animated; - (void)transitionToNoDataStateAnimated:(BOOL)animated; - (void)transitionToDataStateAnimated:(BOOL)animated; @end

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@interface AsyncData : NSObject @interface AsyncView : UIView @interface AsyncStatusView : NSObject @interface AsyncViewController : UIViewController

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@interface IIAsyncViewController : UIViewController - (void)reloadAsyncData; - (UIView*)loadStatusView; - (void)willTransitionToNewStateAnimated:(BOOL)animated; - (void)didTransitionToLoadingStateAnimated:(BOOL)animated; - (void)didTransitionToErrorStateAnimated:(BOOL)animated; - (void)didTransitionToDataStateAnimated:(BOOL)animated; - (void)didTransitionToNoDataStateAnimated:(BOOL)animated; @end

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EXAMPLE

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@interface SuchViewController () @property (nonatomic, strong) LaggyBackend *backend; @end @implementation SuchViewController - (void)performAsyncDataRequest { [self.backend thatReallySlowCall:^(id result) { self.asyncView.asyncData.value = result; } error:^(NSError* error) { self.asyncView.asyncData.error = error; }]; } @end

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@interface SuchView () @property (nonatomic, strong) IBOutlet UILabel *label; @end @implementation SuchView - (void)asyncDataApplyValueAnimated:(BOOL)animated { self.label.text = [NSString stringWithFormat: @"Such %@", self.asyncData.value]; } - (BOOL)asyncCanReload { return self.asyncData.error != nil; }

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UNDER THE HOOD

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// In AsyncViewController - (void)viewDidLoad { [self wrapWithStatusView]; // call regular viewDidLoad [super viewDidLoad]; // force an update of the state to loading [self updateState:YES]; [self performAsyncDataRequest]; }

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- (void)wrapWithStatusView { // don't wrap if there's a status view already if (self.statusView) return; // get async view. This is just self.view when first wrapping. UIView *asyncView = (UIView*)self.view; // now create the status view UIView *statusView = [self loadStatusView]; statusView.frame = asyncView.frame; statusView.asyncView = asyncView; asyncView.asyncData.asyncDataDelegate = self; // make main view the wrapping view [super setView:statusView]; }

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@interface UIViewController (UILayoutSupport) // These objects may be used as layout items // in the NSLayoutConstraint API @property(nonatomic,readonly,strong) id topLayoutGuide; @property(nonatomic,readonly,strong) id bottomLayoutGuide; @end

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1. find constraints related to layout guides before wrapping 2. wrap views 3. first layout pass: recreate constraints

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- (NSArray*)findLayoutGuideConstraints:(UIView*)view { NSMutableArray *constraints = [NSMutableArray new]; UIViewController *viewController = [self findViewDelegate:view]; if (!viewController) return; for (NSLayoutConstraint *constraint in view.constraints) { if (constraint.class != [NSLayoutConstraint class]) continue; if (constraint.firstItem == viewController.topLayoutGuide || constraint.secondItem == viewController.topLayoutGuide) { [constraints addObject:@[constraint, @YES, viewController.topLayoutGuide]]; } else if (constraint.firstItem == delegate.bottomLayoutGuide || constraint.secondItem == delegate.bottomLayoutGuide) { [constraints addObject:@[constraint, @NO, viewController.bottomLayoutGuide]]; } } return [constraints copy]; }

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- (UIViewController*)findViewDelegate:(UIView*)view

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- (UIViewController*)findViewDelegate:(UIView*)view { const char *ivarName = [[NSString stringWithFormat:@"_%@Delegate", @"view"] UTF8String]; Ivar ivar = class_getInstanceVariable(view.class, ivarName); UIViewController *delegate = nil; if (ivar) { delegate = object_getIvar(view, ivar); if ([delegate isKindOfClass:[UIViewController class]]) { return delegate; } } return nil; }

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! 

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- (void)reapplyLayoutGuideConstraints:(NSArray*)constraintInfos { UIViewController *viewController = [self findViewDelegate:self]; if (!viewController) return; for (NSArray *constraintInfo in constraintInfos) { NSLayoutConstraint *oldConstraint = constraintInfo[0]; BOOL topGuide = [constraintInfo[1] boolValue]; // replace first and/or second item with new guides id firstItem = oldConstraint.firstItem == constraintInfo[2] ? (topGuide ? viewController.topLayoutGuide : viewController.bottomLayoutGuide) : : oldConstraint.firstItem; id secondItem = oldConstraint.secondItem == constraintInfo[2] ? (topGuide ? viewController.topLayoutGuide : viewController.bottomLayoutGuide) : oldConstraint.secondItem; // Create new constraint NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:firstItem attribute:oldConstraint.firstAttribute relatedBy:oldConstraint.relation toItem:secondItem attribute:oldConstraint.secondAttribute multiplier:oldConstraint.multiplier constant:oldConstraint.constant]; [self addConstraint:constraint]; } }

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DETAILS

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MASSIVE VIEW CONTROLLER A REPRISE

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MASSIVE VIEW CONTROLLER IPHONE - 1.0 // Lines of code, including whitespace * Portfolio: .h: 14, .m: 523 * Hotspot: * HSViewController .h: 25, .m: 716 * HSBoxController .h: 44, .m: 370

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MASSIVE VIEW CONTROLLER IPHONE - 1.2 // Lines of code, including whitespace * Portfolio: .h: 16, .m: 373 * Hotspot: * HSViewController: .h: 28, .m: 539 * HSBoxController: 41.h, .m: 108

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MASSIVE VIEW CONTROLLER IPHONE - 1.0 VS 1.2 * Portfolio: .h: 114%, .m: 71% * Hotspot: * HSViewController: .h: 112%.h, .m: 75% * HSBoxController: .h: 93%.h, .m: 29%

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¯\_()_/¯

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TAKEAWAY

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1. embrace View Controller Containment 2. reduce dependencies 3. avoid boilerplate 4. DRY 5. testable