Some Closure After Missing the Block Party

Blocks are a powerful programming pattern introduced in iOS 4. Block-based APIs are used throughout the system now and you really need to be comfortable with the concept, especially with Swift on the horizon. We’ll take a look at the key concepts needed to work with blocks, some of the frameworks like Grand Central Dispatch that make them powerful, and then see how they’re evolving in Swift.

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1. Some Closure After Missing the Block Party Curtis Herbert @parrots
2. What is a block?
3. ^() { //do some awesome stuff };
4. void (^myBlock)() = ^() { NSLog(@“Inside!”); }; ! NSLog(@“Outside”); ! myBlock();
5. int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10);
6. int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameters Body Parameter types
7. int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameters Body Parameter types
8. int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Para Body Parameter types
9. int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameter types Body Parameters
10. int (^myBlock)(int) = ^(int a) { return a * 15; }; ! int result = myBlock(10); Definition Implementation Return type Name Parameter types Parameters Body
11. http://f*ckingblocksyntax.com ! ! (or http://goshdarnblocksyntax.com)
12. [UIView animateWithDuration:1 animations:^{ self.view.alpha = 0.0; }]; ! ! [myDictionary enumerateKeysAndObjectsUsingBlock: ^(id k, id v, BOOL *stop) { NSLog(@"%@ => %@", k, v); }];
13. - (void)upload:(NSData *)data failure:(void (^)(NSError *))callback; ! ! ! [server upload:myData failure:^(NSError *error) { NSLog(@“Error!?! %@“, error); }];
14. Blocks + Grand Central Dispatch
15. Queue Types Concurrent Serial 1 2 3 1 2 3
16. 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();
17. - (void)doLotsOfWork { for (int i = 1; i < 100000; i++) { NSLog(@“%l”, i); } } ! ... ! NSLog(@“Before”); ! [self doLotsOfWork]; ! NSLog(@“After”);
18. Don’t block the main thread!
19. NSLog(@“Before”); ! [self performSelectorInBackground: @selector(doLotsOfWork) withObject:nil]; ! NSLog(@“After”);
20. dispatch_async
21. 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”);
22. 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”);
23. 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”);
24. dispatch_after dispatch_once, dispatch_sync, dispatch_apply
25. Blocks + NSOperationQueue
26. NSOperationQueue *myQueue = [[NSOperationQueue alloc] init]; ! [myQueue addOperationWithBlock:^(void){ //Do something awesome }];
27. 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];
28. 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];
29. –Me “Start with GCD”
30. Some gotchas Blocks capture in-scope variables (with the best intentions!)
31. __block NSString *test = @“Hello!; ! void (^myBlock)() = ^(){ test = @“Hello 2!”; }; ! myBlock(); ! NSLog(test);
32. __block __block NSString *test = @“Hello!; ! void (^myBlock)() = ^(){ test = @“Hello 2!”; }; ! myBlock(); ! NSLog(test);
33. weakself pattern self.errorHandler = ^(){ [self displayAlert:@“Oh No!”]; };
34. 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"
35. Closures in Swift
36. {(parameterTypes) -> (returnType) in //do some awesome stuff }
37. {(name: String) -> (Bool) in return countElements(name) > 6 }
38. http://f*ckingclosuresyntax.com ! (or http://goshdarnclosuresyntax.com)
39. dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), { //Background Task ! dispatch_async(dispatch_get_main_queue(), { //Update the UI }) } )
40. __block var test = "Hello, playground” ! var myClosure: () { test = "Hello Again!" } ! myClosure ! println(test)
41. weakself: easier self.errorHandler = { self.displayAlert(“Oh No!”) }
42. weakself: easier self.errorHandler = { [unowned self] in self.displayAlert(“Oh No!”) }
43. Further reading WWDC 2010: Introducing Blocks and Grand Central Dispatch on iPhone The Swift Programming Language iBook http://goshdarnblocksyntax.com http://goshdarnclosuresyntax.com