«ReactiveCocoa и MVVM» — Николай Касьянов, SoftWear
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The document discusses ReactiveCocoa and its use alongside the MVVM architecture in Objective-C applications. It highlights how ReactiveCocoa simplifies asynchronous programming through streams, futures, and signals, while addressing the challenges of learning and debugging. Additionally, it presents the benefits of MVVM, including separation of concerns, reusability, and improved testability, and illustrates examples of integrating ReactiveCocoa with MVVM patterns.
![CALLBACK HELL
void (^completion)(UIImage *) = ...
id token = [self loadImage:url completion:^(NSData *data, NSError *error) {
if (data == nil) {
completion(defaultImage);
}
else {
[self unpackImageFromData:data completion:^(UIImage *image) {
if (image == nil) { // unpacking failed
completion(defaultImage);
}
else {
completion(image);
}
}]
}
}];
!
// client code
[imageLoader cancel:token];
!](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-3-320.jpg)
![RACSignal *image =
[[[self rac_imageFromURL:url] flattenMap:^(NSData *data) {
return [self rac_unpackedImageFromData:data];
}]
catchTo:[RACSignal return:defaultImage]];
!
// client code:
RAC(cell.imageView, image) =
[image takeUntil:cell.rac_prepareForReuseSignal];](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-5-320.jpg)
![RACSignal *allPosts =
[RACSignal createSignal:^(id <RACSubscriber> s) {
[httpClient GET:@"/posts.json" success:^(NSArray *posts) {
[s sendNext:posts];
[s sendCompleted];
} failure:^(NSError *error) {
[s sendError:error];
}];
!
!
}];
return [RACDisposable disposableWithBlock:^{
[operation cancel];
}];
RACSignal *posts =
[[allPosts flattenMap:^(NSArray *items) {
return items.rac_signal;
}] filter:^(Post *post) {
return post.hasComments;
}];
// Nothing happened yet
!
[[posts collect] subscribeNext:^(NSArray *items) { NSLog(@"Posts: %@", items) }];
!
RACDisposable *disposable =
[posts subscribeCompleted:^{ NSLog(@"Done"); }];
// Ooops network request performed twice :(
!
[disposable dispose];](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-7-320.jpg)
![RACSignal *searchResults =
[[[[textField.rac_textSignal throttle:1] filter:^(NSString *query) {
return query.length > 2;
}] map:^(NSString *query) {
return [[[networkClient itemsMatchingQuery:query]
doError:^(NSError *error) {
[self displayError:error];
}]
catchTo:[RACSignal empty]];
}] switchToLatest];
!
// Automatically disposes subscription on self deallocation
// cancelation running network request (if any)
RAC(self, items) = searchResults;](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-9-320.jpg)
![RACSignal *range = [[[RACSignal merge:@[
[self rac_signalForSelector:@selector(tableView:willDisplayCell...)]
[self rac_signalForSelector:@selector(tableView:didEndDisplayingCell...)]
]] map:^(RACtuple *args) {
UITableView *tableView = args[0];
NSArray *indexPaths = tableView.indexPathsForVisibleRows;
NSRange range = NSMakeRange([indexPaths[0] row], indexPaths.count);
return [NSValue valueWithRange:range];
}];
!
[self rac_liftSelector:@selector(updateVisibleRange:)
withSignals:range, nil];](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-11-320.jpg)
![CONCURRENCY
•
RACScheduler
•
-deliverOn:
and -subscribeOn:
- (RACSignal *)itemsFromDB {
return [RACSignal createSignal:^(id <RACSubscriber> subscriber) {
NSArray *items = [sqliteWrapper fetchItemsFromTable:@"posts"];
!
[subscriber sendNext:items];
[subscriber sendCompleted];
!
}
!
}];
return nil;
[[[[self itemsFromDB]
subscribeOn:[RACScheduler scheduler]]
deliverOn:[RACScheduler mainThreadScheduler]]
subscribeNext:^(NSArray *items) {
self.items = items;
}];](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-12-320.jpg)
![@interface LoginViewModel : NSObject
!
@property (nonatomic, copy) NSString *login;
@property (nonatomic, copy) NSString *password;
!
@property (nonatomic, strong, readonly) RACCommand *login;
!
@end
!
!
// Somewhere in view controller
id viewTerminal = loginField.rac_newTextChannel;
id modelTerminal = RACChannelTo(viewModel, login);
!
[[viewTerminal map:^(NSString *value) {
return [value lowercaseString];
}] subscribe:modelTerminal];
[modelTerminal subscribe:viewTerminal];
!
loginButton.rac_command = viewModel.login;
[self rac_liftSelector:@selector(displayError:)
withSignals:viewModel.login.errors, nil];
!
RAC(spinner, animating) = viewModel.login.executing;](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-23-320.jpg)
![RACSignal *networkReachable = RACObserve(httpClient, reachable);
!
RACCommand *login = [[RACCommand alloc]
initWithEnabled:networkReachable
signalBlock:^(id _) {
// Boolean signal, sends @YES on success
return [self.backendClient loginWithLogin:self.login
password:self.password];
}];
!
RAC(self, loggedIn) = [[login.executionSignals switchToLatest]
startWith:@NO];](https://image.slidesharecdn.com/racandmvvm-140303050303-phpapp01/85/ReactiveCocoa-MVVM-SoftWear-25-320.jpg)
«ReactiveCocoa и MVVM» — Николай Касьянов, SoftWear
- 1. REACTIVE COCOA & MVVM Николай Касьянов
- 2. REACTIVE COCOA • Objective-C framework for processing and composing streams • Unifies async Cocoa patterns: callbacks, delegates, KVO, notifications • Very composable • Helps to minimize state • Inspired by Reactive Extensions for .NET
- 3. CALLBACK HELL void (^completion)(UIImage *) = ... id token = [self loadImage:url completion:^(NSData *data, NSError *error) { if (data == nil) { completion(defaultImage); } else { [self unpackImageFromData:data completion:^(UIImage *image) { if (image == nil) { // unpacking failed completion(defaultImage); } else { completion(image); } }] } }]; ! // client code [imageLoader cancel:token]; !
- 4. FUTURES • Future can either complete with a value or reject with an error • JavaScript Promises/A+ • There are some Objective-C implementations • RAC can into futures too
- 5. RACSignal *image = [[[self rac_imageFromURL:url] flattenMap:^(NSData *data) { return [self rac_unpackedImageFromData:data]; }] catchTo:[RACSignal return:defaultImage]]; ! // client code: RAC(cell.imageView, image) = [image takeUntil:cell.rac_prepareForReuseSignal];
- 6. RACSignal • A stream of values • One can subscribe to new value, error or completion • Supports functional constructs: map, filter, flatMap, reduce etc • Сold or hot • A monad
- 7. RACSignal *allPosts = [RACSignal createSignal:^(id <RACSubscriber> s) { [httpClient GET:@"/posts.json" success:^(NSArray *posts) { [s sendNext:posts]; [s sendCompleted]; } failure:^(NSError *error) { [s sendError:error]; }]; ! ! }]; return [RACDisposable disposableWithBlock:^{ [operation cancel]; }]; RACSignal *posts = [[allPosts flattenMap:^(NSArray *items) { return items.rac_signal; }] filter:^(Post *post) { return post.hasComments; }]; // Nothing happened yet ! [[posts collect] subscribeNext:^(NSArray *items) { NSLog(@"Posts: %@", items) }]; ! RACDisposable *disposable = [posts subscribeCompleted:^{ NSLog(@"Done"); }]; // Ooops network request performed twice :( ! [disposable dispose];
- 8. STREAMS • Powerful abstraction • Streams for futures is like iterables for scalar values • Umbrella concept for asynchronous Cocoa patterns • You can even use signals as values. Yo dawg…
- 9. RACSignal *searchResults = [[[[textField.rac_textSignal throttle:1] filter:^(NSString *query) { return query.length > 2; }] map:^(NSString *query) { return [[[networkClient itemsMatchingQuery:query] doError:^(NSError *error) { [self displayError:error]; }] catchTo:[RACSignal empty]]; }] switchToLatest]; ! // Automatically disposes subscription on self deallocation // cancelation running network request (if any) RAC(self, items) = searchResults;
- 10. DEALING WITH IMPERATIVE API • Property binding (one-way and two-way) • Selector lifting (-rac_liftSelector:withSignals:) • Signals from selector (-rac_signalForSelector:) • Operators for injecting side-effects: doNext, doError, initially, finally
- 11. RACSignal *range = [[[RACSignal merge:@[ [self rac_signalForSelector:@selector(tableView:willDisplayCell...)] [self rac_signalForSelector:@selector(tableView:didEndDisplayingCell...)] ]] map:^(RACtuple *args) { UITableView *tableView = args[0]; NSArray *indexPaths = tableView.indexPathsForVisibleRows; NSRange range = NSMakeRange([indexPaths[0] row], indexPaths.count); return [NSValue valueWithRange:range]; }]; ! [self rac_liftSelector:@selector(updateVisibleRange:) withSignals:range, nil];
- 12. CONCURRENCY • RACScheduler • -deliverOn: and -subscribeOn: - (RACSignal *)itemsFromDB { return [RACSignal createSignal:^(id <RACSubscriber> subscriber) { NSArray *items = [sqliteWrapper fetchItemsFromTable:@"posts"]; ! [subscriber sendNext:items]; [subscriber sendCompleted]; ! } ! }]; return nil; [[[[self itemsFromDB] subscribeOn:[RACScheduler scheduler]] deliverOn:[RACScheduler mainThreadScheduler]] subscribeNext:^(NSArray *items) { self.items = items; }];
- 13. ISSUES • Steep learning curve • Runtime overhead • Tricky debugging: crazy call stacks, lots of asynchrony, retain cycles • You’ll need to deal with imperative Cocoa API anyway • Losing last bits of type information
- 14. MVVM
- 16. MVVM • Model – View – View Model • An alternative to MVC • MVC is fine, but… • Meet UIViewController, The Spaghetti Monster
- 18. MVVM • MVVM knows nothing about a view • MVVM uses underlying layers (persistence, web service clients, cache) to populate view data • You can even use it with ncurses
- 19. WHY MVVM? • Clear separation between view and presentation logiс • Reusability across different views and even platforms • Testability • View models are models • Persistence can be hidden behind view model
- 20. YOU ALREADY CLOSER TO MVVM THAN YOU THINK Big monolithic view controllers ! External data sources, data converters & services ! MVVM
- 21. @interface UserRepositoryViewModel : NSObject ! // KVOable properties @property (nonatomic, copy, readonly) NSArray *items; @property (nonatomic, strong, readonly) User *selectedUser; @property (nonatomic, readonly) BOOL isLoading; ! - (void)refreshItems; - (void)selectItemAtIndex; ! @end
- 22. MVVM + RAC • KVO with RACObserve • One-way binding: RAC(object, • Two-way binding: RACChannel • RACCommand keyPath) = signal;
- 23. @interface LoginViewModel : NSObject ! @property (nonatomic, copy) NSString *login; @property (nonatomic, copy) NSString *password; ! @property (nonatomic, strong, readonly) RACCommand *login; ! @end ! ! // Somewhere in view controller id viewTerminal = loginField.rac_newTextChannel; id modelTerminal = RACChannelTo(viewModel, login); ! [[viewTerminal map:^(NSString *value) { return [value lowercaseString]; }] subscribe:modelTerminal]; [modelTerminal subscribe:viewTerminal]; ! loginButton.rac_command = viewModel.login; [self rac_liftSelector:@selector(displayError:) withSignals:viewModel.login.errors, nil]; ! RAC(spinner, animating) = viewModel.login.executing;
- 24. RACCommand • Runs signal block on -execute: and subscribes to its result • Multicasts execution signals to consumers • Multicasts inner signal errors to consumers • Enabled/disabled state can be controlled by a bool signal • Exposes execution state (running/not running) • Can be bound to UI control
- 25. RACSignal *networkReachable = RACObserve(httpClient, reachable); ! RACCommand *login = [[RACCommand alloc] initWithEnabled:networkReachable signalBlock:^(id _) { // Boolean signal, sends @YES on success return [self.backendClient loginWithLogin:self.login password:self.password]; }]; ! RAC(self, loggedIn) = [[login.executionSignals switchToLatest] startWith:@NO];
- 26. • Make no assumptions about a view • Expose bindable properties or signals • Expose commands to consumers • Throttle/unsubscribe signals when view is inactive
- 27. ANY QUESTIONS?