iOS. 
 Advanced Programming Techniques.
 Vasyl Krychun
 

Agenda • Multithreading • Networking • Runtime • General tricks 

Task #1 Application with responsive UI, silent data synchronization and offline mode support. 

Multithreading Main thread Background thread Data Model View 

Solution Main thread Background thread Data Model (Core Data) View Data Model (Core Data) 

MVC 

• NSThread+NSRunLoop • GCD (Grand Central Dispatch) • NSOperation+NSOperationQueue ! ! ! Approaches 

Data Synchronization • NSManagedObjectContextDidSaveNotification 

UI notification • NSFetchedResultsController 

Task #2 Hybrid app with web UI. Interface between UI and native functionality. 

Benefits 

Native bridge
 (approach #1) Native: - (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType: (UIWebViewNavigationType)navigationType; ! JS: window.location = http://something.com?func=¶ms='list of params (json)'&callback=jsFunc; 

Native bridge
 (approach #2) • Custom NSURLProtocol 

Native bridge
 (approach #3) • XMLHttpRequest extension with window.location 

Task #3 Custom synchronous request implementation with delegation. 

- (NSDictionary*) sendRequest: (NSURLRequest*) request { _connecion = [[NSURLConnection alloc] initWithRequest: request delegate:self startImmediately:NO]; NSRunLoop *runLoop = [NSRunLoop currentRunLoop]; [_connecion scheduleInRunLoop:runLoop forMode:NSDefaultRunLoopMode]; [_connecion start]; do { [runLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; } while (!_isDone && !_isCanceled); [_connecion cancel]; return _responseData; } Synchronous request 

Task #4 Observing an object change 

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if ([keyPath isEqualToString:@"synchronized"]) { //DO something! } } KVO 

+ (NSSet *)keyPathsForValuesAffectingSynchronized { unsigned int num_props; objc_property_t *prop_list = class_copyPropertyList(self, &num_props); NSMutableSet * propSet = [NSMutableSet set]; for( unsigned int i = 0; i < num_props; i++ ) { NSString * propName = [NSString stringWithFormat:@"%s", property_getName(prop_list[i])]; if(![propName isEqualToString:@"synchronized"] ) { [propSet addObject:propName]; } } free(prop_list); return propSet; } KVO 

Tricks • Method swizzling • Network operations when app in background • Blocks as arguments • Device unique identifier ! 

Method swizzling Class class = [self class]; SEL originalSelector = @selector(viewWillAppear:); SEL swizzledSelector = @selector(own_viewWillAppear:); Method originalMethod = class_getInstanceMethod(class, originalSelector); Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector); method_exchangeImplementations(originalMethod, swizzledMethod); 

App in background UIApplication *app = [UIApplication sharedApplication]; __block UIBackgroundTaskIdentifier bgTask; bgTask = [app beginBackgroundTaskWithExpirationHandler:^{ NSLog(@"background task has ended"); [app endBackgroundTask:bgTask]; }]; 

Blocks as arguments - (void) downloadFile: (NSURL*) url options: (NSDictionary*) options completionBlock:(void(^)(BOOL result)) completionBlock progressBlock:(void(^)(long long data_size, long long downloaded_data_size)) progressBlock; ! typedef void (^CompletionEvent) (BOOL result); typedef void (^ProgressEvent) (long long data_size, long long downloaded_data_size); ! - (void) downloadFile: (NSURL*) url options: (NSDictionary*) options completionBlock:(CompletionEvent) completionBlock progressBlock:(ProgressEvent) progressBlock; 

Blocks as arguments - (void) downloadFile: (NSURL*) url options: (NSDictionary*) options completionBlock:(CompletionEvent) completionBlock progressBlock:(ProgressEvent) progressBlock { //downloading is completed completionBlock (YES); //downloading in progress progressBlock(123334,456); } ! [self downloadFile:url options:options completionBlock:^(BOOL result) { if (result) { //DO smth. } } progressBlock:^(long long data_size, long long downloaded_data_size) { //handle data_size and downloaded_data_size }]; 

Device unique Id + (NSString*) getUniqueDeviceIdentifier { KeychainItemWrapper *wrapper = [[KeychainItemWrapper alloc] initWithIdentifier:@"yourApplication" accessGroup:nil]; [wrapper setObject:(__bridge id)kSecAttrAccessibleAlways forKey:(__bridge id)kSecAttrAccessible]; NSString *uniqueIdentifier = [wrapper objectForKey:(__bridge id)kSecAttrAccount]; if (!uniqueIdentifier || [uniqueIdentifier length] == 0) { CFUUIDRef newUniqueId = CFUUIDCreate(kCFAllocatorDefault); uniqueIdentifier = (__bridge_transfer NSString*)CFUUIDCreateString(kCFAllocatorDefault, newUniqueId); CFRelease(newUniqueId); [wrapper setObject:uniqueIdentifier forKey:(__bridge id)kSecAttrAccount]; } return uniqueIdentifier; } 

Questions