One Way Flow of Data - Speaker Deck

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RETHINKING IOS APP ARCHITECTURE USING A ONE WAY DATA FLOW kat hawthorne, software engineer @square #hearandnow | @khhawthorne

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#hearandnow | @khhawthorne

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VIEW CONTROLLERS OUT OF CONTROL SHARED DATA CAUSES HARD TO DISCOVER BUGS CODE WITH TOO MUCH RESPONSIBILITY IS HARD TO TEST COMMON PROBLEMS IN IOS APPLICATIONS #hearandnow | @khhawthorne

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VIEW CONTROLLERS HAVE TOO MUCH RESPONSIBILITY SHARED DATA CAUSES HARD TO DISCOVER BUGS CODE WITH TOO MUCH RESPONSIBILITY IS HARD TO TEST #hearandnow | @khhawthorne

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YOUR CART IS EMPTY CART ADD ITEMS TO CHECKOUT #hearandnow | @khhawthorne

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SHIRT $20 CALCULATE TOTAL CART #hearandnow | @khhawthorne

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SKU ‘1234’ NOT FOUND CHECKOUT SHIRT $20 CALCULATE TOTAL CART #hearandnow | @khhawthorne

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SHIRT $20 CHECKOUT 1 ITEM FOR $21 TAX $1 TOTAL $21 CART #hearandnow | @khhawthorne

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SHIRT $20 CHECKOUT 1 ITEM FOR $21 TAX $1 TOTAL $21 [JIRA] (LST-99) CHECKOUT BUTTON COLOR DOES NOT UPDATE CART #hearandnow | @khhawthorne

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VIEW CONTROLLERS HAVE TOO MUCH RESPONSIBILITY SHARED DATA CAUSES HARD TO DISCOVER BUGS CODE WITH TOO MUCH RESPONSIBILITY IS HARD TO TEST #hearandnow | @khhawthorne

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SHIRT $20 CART CALCULATE TOTAL HAT $20 X #hearandnow | @khhawthorne

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SHIRT $20 CART CALCULATE TOTAL HAT $20 X [JIRA] (LST-100) APP CRASHES WHEN CALCULATING TOTAL AND DELETING ITEM SIMULTANEOUSLY* #hearandnow | @khhawthorne

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VIEW CONTROLLERS HAVE TOO MUCH RESPONSIBILITY SHARED DATA CAUSES HARD TO DISCOVER BUGS CODE WITH TOO MUCH RESPONSIBILITY IS HARD TO TEST #hearandnow | @khhawthorne

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EMPTY CART CART WITH ITEMS VIEW CONTROLLER TESTS #hearandnow | @khhawthorne

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EMPTY CART CART WITH ITEMS ERROR STATE SUCCESS STATE VIEW CONTROLLER TESTS #hearandnow | @khhawthorne

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EMPTY CART CART WITH ITEMS ERROR STATE SUCCESS STATE ERROR STATE SUCCESS STATE VIEW CONTROLLER TESTS #hearandnow | @khhawthorne

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EMPTY CART CART WITH ITEMS ERROR STATE SUCCESS STATE ERROR STATE SUCCESS STATE AND SO ON… VIEW CONTROLLER TESTS #hearandnow | @khhawthorne

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ONE WAY FLOW OF DATA: THE CYCLE RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT RENDERER #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT CONTEXT #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT PRESENTER #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT VIEW MODEL #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT VIEW CONTROLLER #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT VIEW #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT SERVICE #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT REPOSITORY #hearandnow | @khhawthorne

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ONE WAY FLOW OF DATA: PUTTING IT TOGETHER RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT #hearandnow | @khhawthorne

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AN EXAMPLE: ADDING AN ITEM TO THE CART #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT RENDERER class Renderer { func render() { let cartViewModel = CartPresenter.present( accountService: context.accountService, cartService: context.cartService, errorService: context.errorService, itemService: context.itemService ) cartViewController.update(cartViewModel) } } #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT CONTEXT class AppContext { private(set) lazy var cartService: CartService = CartService( cartState: self.cartState, catalogService: self.catalogService, accountService: self.accountService, render: self.render ) } #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT PRESENTER final class CartPresenter { class func present( accountService: AccountService, cartService: CartService, errorService: ErrorService, itemService: ItemService ) -> CartViewModel? {…} } #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT VIEW MODEL struct CartViewModel { let preSubtotalLineItems: [LineItem] let emptyCartMessage: String? let displayTotal: String? … } #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT VIEW CONTROLLER final class CartViewController : UIViewController { private(set) cartView: CartView = CartView() func update(viewModel: CartViewModel?){ cartView.emptyCartMessage = viewModel.emptyCartMessage cartView.displayTotalLabel = viewModel.displayTotal … } } #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT VIEW final class CartView : UIView { let emptyCartMessage: UILabel let displayTotalLabel: UILabel … } #hearandnow | @khhawthorne

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RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT SERVICE class CartService { func addSKU(sku: String) { let item = catalog.getItem(sku: SKU) let cart = self.cart.mutableCopy() cart.mutableLineItems.addItemization(item) self.cart = cart.copy() render() } } #hearandnow | @khhawthorne

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ONE WAY FLOW OF DATA: PUTTING IT TOGETHER RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT #hearandnow | @khhawthorne

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VIEW CONTROLLERS OUT OF CONTROL SHARED DATA CAUSES HARD TO DISCOVER BUGS CODE WITH TOO MUCH RESPONSIBILITY IS HARD TO TEST COMMON PROBLEMS IN IOS APPLICATIONS #hearandnow | @khhawthorne

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MULTI-LAYERED ARCHITECTURE SINGLE RESPONSIBILITY PRINCIPLE VIEW CONTROLLERS HAVE TOO MUCH RESPONSIBILITY LESS CODE = LESS MENTAL OVERHEAD #hearandnow | @khhawthorne

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MINIMAL STATE IN THE APP CLEAR DELINEATION OF WHAT CAN MODIFY STATE SHARED DATA CAUSES HARD TO DISCOVER BUGS ONE WAY FLOW OF DATA ELIMINATES UNEXPECTED BEHAVIOR #hearandnow | @khhawthorne

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THIN APPLICATION LAYERS DEPENDENCY INJECTION RATHER THAN RELYING ON SHARED STATE CODE WITH TOO MUCH RESPONSIBILITY IS HARD TO TEST #hearandnow | @khhawthorne

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ONE WAY FLOW OF DATA: PUTTING IT TOGETHER RENDERER PRESENTER VIEW CONTROLLER VIEW SERVICE REPOSITORY VIEW MODEL CONTEXT #hearandnow | @khhawthorne

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kat hawthorne @khhawthorne [email protected] #hearandnow | @khhawthorne