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Some Closure After Missing the Block Party Curtis Herbert @parrots

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What is a block?

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^() { //do some awesome stuff };

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void (^myBlock)() = ^() { NSLog(@“Inside!”); }; ! NSLog(@“Outside”); ! myBlock();

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int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10);

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int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameters Body Parameter types

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int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameters Body Parameter types

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int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Para Body Parameter types

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int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameter types Body Parameters

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int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameter types Parameters Body

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http://f*ckingblocksyntax.com ! ! (or http://goshdarnblocksyntax.com)

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[UIView animateWithDuration:1 animations:^{ self.view.alpha = 0.0; }]; ! ! [myDictionary enumerateKeysAndObjectsUsingBlock: ^(id k, id v, BOOL *stop) { NSLog(@"%@ => %@", k, v); }];

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- (void)upload:(NSData *)data failure:(void (^)(NSError *))callback; ! ! ! [server upload:myData failure:^(NSError *error) { NSLog(@“Error!?! %@“, error); }];

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Blocks + Grand Central Dispatch

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Queue Types Concurrent Serial 1 2 3 1 2 3

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dispatch_get_global_queue() (concurrent) • DISPATCH_QUEUE_PRIORITY_BACKGROUND • DISPATCH_QUEUE_PRIORITY_LOW • DISPATCH_QUEUE_PRIORITY_NORMAL • DISPATCH_QUEUE_PRIORITY_HIGH dispatch_get_main_queue() (serial) dispatch_queue_create();

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- (void)doLotsOfWork { for (int i = 1; i < 100000; i++) { NSLog(@“%l”, i); } } ! ... ! NSLog(@“Before”); ! [self doLotsOfWork]; ! NSLog(@“After”);

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Don’t block the main thread!

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NSLog(@“Before”); ! [self performSelectorInBackground: @selector(doLotsOfWork) withObject:nil]; ! NSLog(@“After”);

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dispatch_async

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NSLog(@“Before”); ! dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //Background Task for (int i = 1; i < 100000; i++) { NSLog(@“%l”, i); } } ); ! NSLog(@“After”);

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NSLog(@“Before”); ! dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //Background Task for (int i = 1; i < 100000; i++) { NSLog(@“%l”, i); } ! dispatch_async(dispatch_get_main_queue(),^{ //Update the UI }); } ); ! NSLog(@“After”);

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NSLog(@“Before”); ! dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //Background Task ! dispatch_async(dispatch_get_main_queue(),^{ //Update the UI }); } ); ! NSLog(@“After”);

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dispatch_after dispatch_once, dispatch_sync, dispatch_apply

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Blocks + NSOperationQueue

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NSOperationQueue *myQueue = [[NSOperationQueue alloc] init]; ! [myQueue addOperationWithBlock:^(void){ //Do something awesome }];

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NSOperationQueue *myQueue = [[NSOperationQueue alloc] init]; ! NSBlockOperation *operation = [[NSBlockOperation alloc] init]; ! [operation addExecutionBlock:^{ //Do something awesome if (!operation.isCancelled) { //Keep doing awesome stuff } }]; ! [myQueue addOperation:operation]; ! [operation cancel];

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NSBlockOperation *operation = [[NSBlockOperation alloc] init]; [operation addExecutionBlock:^{ //Do something awesome }]; ! NSBlockOperation *operation1 = [[NSBlockOperation alloc] init]; [operation1 addExecutionBlock:^{ //Do something else awesome }]; [operation1 addDependency:operation]; ! [myQueue addOperation:operation]; [myQueue addOperation:operation1];

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–Me “Start with GCD”

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Some gotchas Blocks capture in-scope variables (with the best intentions!)

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__block NSString *test = @“Hello!; ! void (^myBlock)() = ^(){ test = @“Hello 2!”; }; ! myBlock(); ! NSLog(test);

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__block __block NSString *test = @“Hello!; ! void (^myBlock)() = ^(){ test = @“Hello 2!”; }; ! myBlock(); ! NSLog(test);

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weakself pattern self.errorHandler = ^(){ [self displayAlert:@“Oh No!”]; };

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weakself pattern _weak typeof(self) weakSelf = self; self.errorHandler = ^(){ __strong typeof(weakSelf) strongSelf = weakSelf; ! if (strongSelf) { [strongSelf displayAlert:@“Oh No!”]; } }; pod ‘libextobjc’, #import "EXTScope.h"

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Closures in Swift

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{(parameterTypes) -> (returnType) in //do some awesome stuff }

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{(name: String) -> (Bool) in return countElements(name) > 6 }

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http://f*ckingclosuresyntax.com ! (or http://goshdarnclosuresyntax.com)

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dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), { //Background Task ! dispatch_async(dispatch_get_main_queue(), { //Update the UI }) } )

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__block var test = "Hello, playground” ! var myClosure: () { test = "Hello Again!" } ! myClosure ! println(test)

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weakself: easier self.errorHandler = { self.displayAlert(“Oh No!”) }

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weakself: easier self.errorHandler = { [unowned self] in self.displayAlert(“Oh No!”) }

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Further reading WWDC 2010: Introducing Blocks and Grand Central Dispatch on iPhone The Swift Programming Language iBook http://goshdarnblocksyntax.com http://goshdarnclosuresyntax.com