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menu_book Course Curriculum (Objective-C) expand_more

Language and Compilation

Program entry with main Header imports with #import NSString literals NSNumber boxing Scalar numeric types BOOL and YES/NO Format specifiers in NSLog Automatic type inference with __auto_type C structs inside Objective-C Preprocessor conditionals

Objects and Messaging

NSObject subclasses Instance methods Class methods Message sending syntax Properties and dot syntax Custom initializers Designated initializer pattern Class extensions Categories Selectors with @selector

Memory and Ownership

ARC strong references Weak references Copy properties Autorelease pools Retain cycles Weak-strong dance Bridging Core Foundation objects Dealloc cleanup Object lifetime in blocks Unsafe unretained references

Collections and Foundation

NSArray creation NSMutableArray mutation NSDictionary key-value storage NSMutableDictionary updates NSSet uniqueness NSOrderedSet ordering Fast enumeration NSEnumerator traversal NSNull placeholders Collection filtering with predicates

Protocols and Runtime Types

Declaring protocols Protocol conformance Optional protocol methods id dynamic type instancetype return type Lightweight generics Nullability annotations Runtime type checks respondsToSelector Key-value coding

Blocks and Concurrency

Block literals Capturing local variables __block mutable captures Blocks as callbacks Block properties Dispatch queues dispatch_async dispatch_after Dispatch groups Dispatch semaphores

Files Networking and Serialization

Reading text files Writing text files NSURL construction NSURLComponents query items NSData bytes NSJSONSerialization encoding NSJSONSerialization decoding NSUserDefaults storage NSNotificationCenter observers NSError error reporting

Quality and Interop

NSError out parameters NSAssert preconditions XCTest assertions Objective-C exceptions C function interoperability Objective-C++ bridge files Availability checks NS_SWIFT_NAME annotation Debug descriptions Compiler warnings as errors

Objective-C / Blocks and Concurrency

dispatch_after

Learn dispatch_after in Objective-C through a focused explanation, a dedicated topic-specific example, an engineering boundary, and a mastery check.

12 min read • Intermediate

dispatch_after is a focused Objective-C lesson inside Blocks and Concurrency. The example uses the construct named in the lesson directly rather than reusing a generic placeholder.

Trace the example from its inputs through dispatch_after and identify the behavior that would change if that construct were removed or replaced. Pay attention to the language-specific rules shown by the syntax, because neighboring lessons intentionally exercise different mechanisms.

Topic-specific example

objective-c-0058-28cdac45df.m

objectivec Try It Live

dispatch_queue_t q = dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0);
dispatch_async(q, ^{
    NSLog(@"background work");
});
NSArray *check = @[@1,@2,@3]; NSLog(@"%lu", (unsigned long)check.count);

Edge case / engineering note

For dispatch_after, test one realistic boundary: empty data, invalid input, unavailable resources, lifetime/cleanup, type constraints, or concurrency timing where applicable. A successful happy path is not enough to prove the construct is used correctly.

Content source & attribution

Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

dispatch_after Mastery Check →

Dispatch groups