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< p > < a href = "index.html" > IGListKit Docs< / a > (98% documented)< / p >
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< p class = "header-right" > < a href = "https://github.com/Instagram/IGListKit" > < img src = "img/gh.png" / > View on GitHub< / a > < / p >
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Working with Core Data Reference
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< a href = "Constants.html#/c:@IGListKitVersionNumber" > IGListKitVersionNumber< / a >
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< a href = "Constants.html#/c:@IGListKitVersionString" > IGListKitVersionString< / a >
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< a href = "Protocols/IGListAdapterUpdaterDelegate.html" > IGListAdapterUpdaterDelegate< / a >
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< a href = "Type Definitions.html#/c:IGListUpdatingDelegate.h@T@IGListToObjectBlock" > IGListToObjectBlock< / a >
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< a href = "Type Definitions.html#/c:IGListAdapter.h@T@IGListUpdaterCompletion" > IGListUpdaterCompletion< / a >
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< a href = "Functions.html#/c:@F@IGListDiff" > IGListDiff< / a >
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< a href = "Functions.html#/c:@F@IGListDiffExperiment" > IGListDiffExperiment< / a >
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< a href = "Functions.html#/c:@F@IGListDiffPaths" > IGListDiffPaths< / a >
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< h1 id = 'working-with-core-data' class = 'heading' > Working with Core Data< / h1 >
< p > This guide provides details on how to work with < a href = "https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/CoreData/index.html" > Core Data< / a > and < code > IGListKit< / code > .< / p >
< h2 id = 'background' class = 'heading' > Background< / h2 >
< p > The main difference in the setup and architecture of a Core Data and < code > IGListKit< / code > application is the configuration of the model layer. Core Data operates with a mutable model layer, where objects are always passed by reference and the same instance is modified when an object is edited.< / p >
< p > < code > IGListKit< / code > requires an immutable model in order to correctly calculate the diffing between model snapshots and to correctly animate the < code > UICollectionView< / code > .< / p >
< p > In order to satisfy these prerequisites, Core Data < code > NSManagedObject< / code > s should not be used directly as < code > ListDiffable< / code > objects. Instead, a view model (or some sort of token object) should be used to mimic (or act as a placeholder for) the data that will be displayed in the collection view.< / p >
< h2 id = 'further-discussion' class = 'heading' > Further discussion< / h2 >
< p > There are further discussions on this topic at < a href = "https://github.com/Instagram/IGListKit/issues/460" > #460< / a > , < a href = "https://github.com/Instagram/IGListKit/issues/461" > #461< / a > , < a href = "https://github.com/Instagram/IGListKit/issues/407" > #407< / a > .< / p >
< h2 id = 'basic-setup' class = 'heading' > Basic Setup< / h2 >
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< p > The basic setup for Core Data and < code > IGListKit< / code > is the same as the normal setup that is found in the < a href = "https://instagram.github.io/IGListKit/getting-started.html" > Getting Started Guide< / a > . The main difference will be in the setup of the model used in the < code > < a href = "Protocols/IGListAdapterDataSource.html" > IGListAdapterDataSource< / a > < / code > .< / p >
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< h2 id = 'working-with-view-model' class = 'heading' > Working with view model< / h2 >
< h3 id = 'creating-a-view-model' class = 'heading' > Creating a view model< / h3 >
< p > Suppose the Core Data model consist of:< / p >
< pre class = "highlight swift" > < code > < span class = "kd" > extension< / span > < span class = "kt" > User< / span > < span class = "p" > {< / span >
< span class = "kd" > @NSManaged< / span > < span class = "k" > var< / span > < span class = "nv" > firstName< / span > < span class = "p" > :< / span > < span class = "kt" > String< / span >
< span class = "kd" > @NSManaged< / span > < span class = "k" > var< / span > < span class = "nv" > lastName< / span > < span class = "p" > :< / span > < span class = "kt" > String< / span >
< span class = "kd" > @NSManaged< / span > < span class = "k" > var< / span > < span class = "nv" > address< / span > < span class = "p" > :< / span > < span class = "kt" > String< / span >
< span class = "kd" > @NSManaged< / span > < span class = "k" > var< / span > < span class = "nv" > someVariableNotNeededInUI< / span > < span class = "p" > :< / span > < span class = "kt" > String< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< p > A < code > ViewModel< / code > object will contain only the necessary information needed to build UI. The properties of the < code > ViewModel< / code > will be immutable:< / p >
< pre class = "highlight swift" > < code > < span class = "kd" > class< / span > < span class = "kt" > UserViewModel< / span > < span class = "p" > :< / span > < span class = "kt" > NSObject< / span > < span class = "p" > {< / span >
< span class = "k" > let< / span > < span class = "nv" > firstName< / span > < span class = "p" > :< / span > < span class = "kt" > String< / span >
< span class = "k" > let< / span > < span class = "nv" > lastName< / span > < span class = "p" > :< / span > < span class = "kt" > String< / span >
< span class = "k" > let< / span > < span class = "nv" > address< / span > < span class = "p" > :< / span > < span class = "kt" > String< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< p > We recommend writing a helper method to translate Core Data objects into < code > ViewModel< / code > objects:< / p >
< pre class = "highlight swift" > < code > < span class = "kd" > extension< / span > < span class = "kt" > UserViewModel< / span > < span class = "p" > {< / span >
< span class = "kd" > static< / span > < span class = "kd" > func< / span > < span class = "nf" > fromCoreData< / span > < span class = "p" > (< / span > < span class = "nv" > user< / span > < span class = "p" > :< / span > < span class = "kt" > User< / span > < span class = "p" > )< / span > < span class = "o" > -> < / span > < span class = "kt" > UserViewModel< / span > < span class = "p" > {< / span >
< span class = "c1" > // - Note: For avoiding Core Data threading violation, the following code should be wrapped in a< / span >
< span class = "c1" > // user.managedObjectContext?.performAndWait {}< / span >
< span class = "k" > return< / span > < span class = "kt" > UserViewModel< / span > < span class = "p" > (< / span > < span class = "nv" > firstName< / span > < span class = "p" > :< / span > < span class = "n" > user< / span > < span class = "o" > .< / span > < span class = "n" > firstName< / span > < span class = "p" > ,< / span > < span class = "nv" > lastName< / span > < span class = "p" > :< / span > < span class = "n" > user< / span > < span class = "o" > .< / span > < span class = "n" > lastName< / span > < span class = "p" > ,< / span > < span class = "nv" > address< / span > < span class = "p" > :< / span > < span class = "n" > user< / span > < span class = "o" > .< / span > < span class = "n" > lastName< / span > < span class = "p" > )< / span >
< span class = "p" > }< / span >
< span class = "p" > }< / span >
< / code > < / pre >
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< p > The < code > < a href = "Protocols/IGListDiffable.html" > IGListDiffable< / a > < / code > protocol is implemented on the < code > ViewModel< / code > layer:< / p >
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< pre class = "highlight swift" > < code > < span class = "kd" > extension< / span > < span class = "kt" > UserViewModel< / span > < span class = "p" > :< / span > < span class = "kt" > ListDiffable< / span > < span class = "p" > {< / span >
< span class = "kd" > public< / span > < span class = "kd" > func< / span > < span class = "nf" > diffIdentifier< / span > < span class = "p" > ()< / span > < span class = "o" > -> < / span > < span class = "kt" > NSObjectProtocol< / span > < span class = "p" > {< / span >
< span class = "k" > return< / span > < span class = "kt" > NSString< / span > < span class = "p" > (< / span > < span class = "nv" > string< / span > < span class = "p" > :< / span > < span class = "n" > firstName< / span > < span class = "o" > +< / span > < span class = "n" > lastName< / span > < span class = "p" > )< / span >
< span class = "p" > }< / span >
< span class = "kd" > public< / span > < span class = "kd" > func< / span > < span class = "nf" > isEqual< / span > < span class = "p" > (< / span > < span class = "n" > toDiffableObject< / span > < span class = "nv" > object< / span > < span class = "p" > :< / span > < span class = "kt" > ListDiffable< / span > < span class = "p" > ?)< / span > < span class = "o" > -> < / span > < span class = "kt" > Bool< / span > < span class = "p" > {< / span >
< span class = "k" > guard< / span > < span class = "k" > let< / span > < span class = "nv" > toObject< / span > < span class = "o" > =< / span > < span class = "n" > object< / span > < span class = "k" > as?< / span > < span class = "kt" > UserViewModel< / span > < span class = "k" > else< / span > < span class = "p" > {< / span > < span class = "k" > return< / span > < span class = "kc" > false< / span > < span class = "p" > }< / span >
< span class = "k" > return< / span > < span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > firstName< / span > < span class = "o" > ==< / span > < span class = "n" > toObject< / span > < span class = "o" > .< / span > < span class = "n" > firstName< / span >
< span class = "o" > & & < / span > < span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > lastName< / span > < span class = "o" > ==< / span > < span class = "n" > toObject< / span > < span class = "o" > .< / span > < span class = "n" > lastName< / span >
< span class = "o" > & & < / span > < span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > address< / span > < span class = "o" > ==< / span > < span class = "n" > toObject< / span > < span class = "o" > .< / span > < span class = "n" > address< / span >
< span class = "p" > }< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< h2 id = 'setting-up-the-view-model-in-the-adapter-data-source' class = 'heading' > Setting up the view model in the adapter data source< / h2 >
< p > Steps to configure the < code > UICollectionView< / code > with the < code > ViewModel< / code > :< / p >
< ul >
< li > Retrieve Core Data objects< / li >
< li > Transform Core Data objects into ViewModel objects and return them< / li >
< li > Track changes to Core Data objects and update the datasource with them< / li >
< / ul >
< h3 id = 'retrieve-core-data-objects' class = 'heading' > Retrieve Core Data objects< / h3 >
< p > The way objects are retrieved from Core Data is depends on the project. < / p >
< p > Example: Suppose there is a delegate < code > Provider< / code > class with the role of fetching Core Data objects and checking for updates. It can use an < code > NSFetchedResultsController< / code > to leverage on the Core Data framework and rely on automatic notifications for updates.< / p >
< pre class = "highlight swift" > < code > < span class = "kd" > final< / span > < span class = "kd" > class< / span > < span class = "kt" > UserProvider< / span > < span class = "p" > :< / span > < span class = "kt" > NSObject< / span > < span class = "p" > {< / span >
< span class = "kd" > private< / span > < span class = "kd" > lazy< / span > < span class = "k" > var< / span > < span class = "nv" > userFetchResultController< / span > < span class = "p" > :< / span > < span class = "kt" > NSFetchedResultsController< / span > < span class = "o" > < < / span > < span class = "kt" > User< / span > < span class = "o" > > < / span > < span class = "o" > =< / span > < span class = "p" > {< / span >
< span class = "k" > let< / span > < span class = "nv" > fetchRequest< / span > < span class = "p" > :< / span > < span class = "kt" > NSFetchRequest< / span > < span class = "o" > < < / span > < span class = "kt" > User< / span > < span class = "o" > > < / span > < span class = "o" > =< / span > < span class = "kt" > NSFetchRequest< / span > < span class = "p" > (< / span > < span class = "nv" > entityName< / span > < span class = "p" > :< / span > < span class = "s" > "User"< / span > < span class = "p" > )< / span >
< span class = "c1" > // sort descriptors and predicates < / span >
< span class = "c1" > // ...< / span >
< span class = "k" > let< / span > < span class = "nv" > fetchResultController< / span > < span class = "o" > =< / span > < span class = "kt" > NSFetchedResultsController< / span > < span class = "p" > (< / span >
< span class = "nv" > fetchRequest< / span > < span class = "p" > :< / span > < span class = "n" > tripsFetchRequest< / span > < span class = "p" > ,< / span >
< span class = "nv" > managedObjectContext< / span > < span class = "p" > :< / span > < span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > coreDataStack< / span > < span class = "o" > .< / span > < span class = "n" > mainQueueManagedObjectContext< / span > < span class = "p" > ,< / span >
< span class = "nv" > sectionNameKeyPath< / span > < span class = "p" > :< / span > < span class = "kc" > nil< / span > < span class = "p" > ,< / span >
< span class = "nv" > cacheName< / span > < span class = "p" > :< / span > < span class = "kc" > nil< / span > < span class = "p" > )< / span >
< span class = "c1" > // Set delegate to track CoreData changes< / span >
< span class = "n" > fetchResultController< / span > < span class = "o" > .< / span > < span class = "n" > delegate< / span > < span class = "o" > =< / span > < span class = "k" > self< / span >
< span class = "k" > return< / span > < span class = "n" > fetchResultController< / span >
< span class = "p" > }()< / span >
< span class = "nf" > init< / span > < span class = "p" > (< / span > < span class = "nv" > coreDataStack< / span > < span class = "p" > :< / span > < span class = "kt" > CoreDataStack< / span > < span class = "p" > )< / span > < span class = "p" > {< / span >
< span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > coreDataStack< / span > < span class = "o" > =< / span > < span class = "n" > coreDataStack< / span >
< span class = "k" > super< / span > < span class = "o" > .< / span > < span class = "nf" > init< / span > < span class = "p" > ()< / span >
< span class = "k" > do< / span > < span class = "p" > {< / span >
< span class = "k" > try< / span > < span class = "n" > userFetchResultController< / span > < span class = "o" > .< / span > < span class = "nf" > performFetch< / span > < span class = "p" > ()< / span >
< span class = "p" > }< / span >
< span class = "k" > catch< / span > < span class = "p" > {< / span >
< span class = "nf" > fatalError< / span > < span class = "p" > (< / span > < span class = "s" > "Cannot Fetch! < / span > < span class = "se" > \(< / span > < span class = "n" > error< / span > < span class = "se" > )< / span > < span class = "s" > "< / span > < span class = "p" > )< / span >
< span class = "p" > }< / span >
< span class = "p" > }< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< h3 id = 'transform-core-data-objects-into-view-models' class = 'heading' > Transform Core Data objects into view models< / h3 >
< pre class = "highlight swift" > < code > < span class = "kd" > func< / span > < span class = "nf" > getUsers< / span > < span class = "p" > ()< / span > < span class = "o" > -> < / span > < span class = "p" > [< / span > < span class = "kt" > UserViewModel< / span > < span class = "p" > ]?< / span > < span class = "p" > {< / span >
< span class = "k" > guard< / span > < span class = "k" > let< / span > < span class = "nv" > users< / span > < span class = "o" > =< / span > < span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > userFetchResultController< / span > < span class = "o" > .< / span > < span class = "n" > fetchedObjects< / span > < span class = "k" > else< / span > < span class = "p" > {< / span > < span class = "k" > return< / span > < span class = "kc" > nil< / span > < span class = "p" > }< / span >
< span class = "c1" > // Here we transform and return ViewModel objects!< / span >
< span class = "k" > return< / span > < span class = "n" > users< / span > < span class = "o" > .< / span > < span class = "n" > flatMap< / span > < span class = "p" > {< / span > < span class = "kt" > UserViewModel< / span > < span class = "o" > .< / span > < span class = "nf" > fromCoreData< / span > < span class = "p" > (< / span > < span class = "nv" > user< / span > < span class = "p" > :< / span > < span class = "nv" > $0< / span > < span class = "p" > )< / span > < span class = "p" > }< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< h3 id = 'track-changes-to-core-data' class = 'heading' > Track changes to Core Data< / h3 >
< p > The < code > Provider< / code > will track changes to the Core Data model by listening to the < code > NSFetchedResultsController< / code > methods and inform the application about this changes via KVO, notifications, delegation, etc.< / p >
< pre class = "highlight swift" > < code > < span class = "kd" > extension< / span > < span class = "kt" > UserProvider< / span > < span class = "p" > :< / span > < span class = "kt" > NSFetchedResultsControllerDelegate< / span > < span class = "p" > {< / span >
< span class = "kd" > func< / span > < span class = "nf" > controllerDidChangeContent< / span > < span class = "p" > (< / span > < span class = "n" > _< / span > < span class = "nv" > controller< / span > < span class = "p" > :< / span > < span class = "kt" > NSFetchedResultsController< / span > < span class = "o" > < < / span > < span class = "kt" > NSFetchRequestResult< / span > < span class = "o" > > < / span > < span class = "p" > )< / span > < span class = "p" > {< / span >
< span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > delegate< / span > < span class = "p" > ?< / span > < span class = "o" > .< / span > < span class = "nf" > performUpdatesForCoreDataChange< / span > < span class = "p" > (< / span > < span class = "nv" > animated< / span > < span class = "p" > :< / span > < span class = "kc" > true< / span > < span class = "p" > )< / span >
< span class = "p" > }< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< h3 id = 'configure-the-datasource' class = 'heading' > Configure the datasource< / h3 >
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< p > The data source retrieves ViewModels and configures the < code > < a href = "Classes/IGListSectionController.html" > IGListSectionController< / a > < / code > with them:< / p >
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< pre class = "highlight swift" > < code > < span class = "kd" > func< / span > < span class = "nf" > objects< / span > < span class = "p" > (< / span > < span class = "k" > for< / span > < span class = "nv" > listAdapter< / span > < span class = "p" > :< / span > < span class = "kt" > ListAdapter< / span > < span class = "p" > )< / span > < span class = "o" > -> < / span > < span class = "p" > [< / span > < span class = "kt" > ListDiffable< / span > < span class = "p" > ]< / span > < span class = "p" > {< / span >
< span class = "k" > return< / span > < span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > userProvider< / span > < span class = "o" > .< / span > < span class = "nf" > getUsers< / span > < span class = "p" > ()< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< h3 id = 'reacting-to-core-data-changes-in-ui' class = 'heading' > Reacting to Core Data changes in UI< / h3 >
< p > The < code > UIViewController< / code > containing the < code > UICollectionView< / code > , will react to the < code > NSFetchedResultController< / code > messages by updating the UI:< / p >
< pre class = "highlight swift" > < code > < span class = "kd" > func< / span > < span class = "nf" > performUpdatesForCoreDataChange< / span > < span class = "p" > (< / span > < span class = "nv" > animated< / span > < span class = "p" > :< / span > < span class = "kt" > Bool< / span > < span class = "p" > )< / span > < span class = "p" > {< / span >
< span class = "c1" > // Updating contents of collection view< / span >
< span class = "k" > self< / span > < span class = "o" > .< / span > < span class = "n" > adapter< / span > < span class = "o" > .< / span > < span class = "nf" > performUpdates< / span > < span class = "p" > (< / span > < span class = "nv" > animated< / span > < span class = "p" > :< / span > < span class = "n" > animated< / span > < span class = "p" > )< / span >
< span class = "p" > }< / span >
< / code > < / pre >
< / section >
< / section >
< section id = "footer" >
2018-05-01 23:54:35 +00:00
< p > © 2018 < a class = "link" href = "https://twitter.com/fbOpenSource" target = "_blank" rel = "external" > Instagram< / a > . All rights reserved. (Last updated: 2018-05-01)< / p >
2018-02-06 23:42:25 +00:00
< p > Generated by < a class = "link" href = "https://github.com/realm/jazzy" target = "_blank" rel = "external" > jazzy ♪♫ v0.9.1< / a > , a < a class = "link" href = "http://realm.io" target = "_blank" rel = "external" > Realm< / a > project.< / p >
2017-05-12 14:19:12 +00:00
< / section >
< / article >
< / div >
< / body >
< / div >
< / html >
