https://www.objc.io/issues/13-architecture/viper/
Protocol is a one to one relationship where a receiving object implements a delegate protocol. A sending object uses it and sends messages (assuming that those methods are implemented) since the receiver promised to comply to the protocol.
First, the Interactor protocol!
The interactor is the middle man between data and the presenter. It has a protocol that says
1) there is an input property from the presenter that forces Interactor to implement findUpcomingItems ( to find upcoming certain (decided by presenter) items or data.
2) there is an output property pointing to presenter that forces Presenter to implement foundUpcomingItems:.
InteractorIO.h
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@protocol InteractorInput <NSObject> - (void)findUpcomingItems; @end @protocol InteractorOutput <NSObject> - (void)foundUpcomingItems:(NSArray *)upcomingItems; @end |
Presenter.h
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@interface Presenter : NSObject <InteractorOutput> @property (nonatomic, strong) id<InteractorInput> interactor; |
Presenter.m
Using the interactor property to force the Interactor component to implement required method(s)
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-(void)updateView { [self.interactor findUpcomingItems]; } |
The interactor property is connected to the Interactor component. Our interactor property (which conforms to InteractorInput), promises that this Interactor component will have the method findUpcomingItems implemented. Thus, say when we want to update the view, we tell the interactor component (through our id interactor property) to call the findUpcomingItems method.
In other words, Interactor can retrieve data for us because it talks to the DB Manager/Entities, thus, we (the Presenter) have an interactor property to the Interactor object so that we can call required Protocol methods to find certain data for us by forcing the Interactor component to implement findUpcomingItems:
Presenter component implements promised required protocol methods
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- (void)foundUpcomingItems:(NSArray *)upcomingItems { if ([upcomingItems count] == 0) { [self.userInterface showNoContentMessage]; } else { [self updateUserInterfaceWithUpcomingItems:upcomingItems]; } } |
Presenter conforms to InteractorOutput because we promise to implement a method foundUpcomingItems: which means we’ll take care of
the data returned by the Interactor.
The Interactor will point a output property to the Presenter. Thus, the output says Presenter must implement foundUpcomingItems:.
Interactor.h
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@interface Interactor : NSObject <InteractorInput> @property (nonatomic, weak) id<InteractorOutput> output; - (instancetype)initWithDataManager:(DataManager *)dataManager; @end |
The Presenter object works with the UIViews/UIViewControllers to display data, thus, we point an output property to
the Presenter object in order to force it to implement foundUpcomingItems:(NSArray*).
The method gets gets the found data
in Presenter, and thus, can have the UIViews/UIViewControllers display it.
Interactor.m
Interactor conforms to InteractorInput, which means we promise to implement a method called findUpcomingItems.
This is be requested by the Presenter/Views throug Presenter’s interactor property.
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- (void)findUpcomingItems { __weak typeof(self) welf = self; NSDate *today = [self.clock today]; NSDate *endOfNextWeek = [[NSCalendar currentCalendar] dateForEndOfFollowingWeekWithDate:today]; [self.dataManager todoItemsBetweenStartDate:today endDate:endOfNextWeek completionBlock:^(NSArray *todoItems) { [welf.output foundUpcomingItems:[welf upcomingItemsFromToDoItems:todoItems]]; }]; } |
Hooking it all up
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Presenter *listPresenter = [[Presenter alloc] init]; Interactor *listInteractor = [[Interactor alloc] initWithDataManager:listDataManager clock:clock]; listInteractor.output = listPresenter; listPresenter.listInteractor = listInteractor; |