Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. It was the main programming language supported by Apple for macOS, iOS, and their respective APIs (Cocoa and Cocoa Touch) before the introduction of Swift.
Objective-C Anti-Patterns Overview
Objective-C, despite being a powerful language for Apple platforms, has several common anti-patterns that can lead to memory leaks, performance issues, and maintainability problems. Here are the most important anti-patterns to avoid when writing Objective-C code.
Not Using ARC (Automatic Reference Counting)
Always use Automatic Reference Counting (ARC) in new Objective-C projects. ARC automatically manages memory for Objective-C objects, reducing the risk of memory leaks and crashes due to over-releasing or accessing deallocated objects.
Strong Reference Cycles
Avoid creating strong reference cycles (retain cycles) where two objects hold strong references to each other. Use weak
or unsafe_unretained
properties for back-references to break these cycles. This is especially important in delegate patterns and parent-child relationships.
Not Using Properties
Use properties instead of direct instance variable access and manual getter/setter methods. Properties provide automatic memory management, KVC/KVO compliance, and make your code more concise and less error-prone.
Not Using Modern Objective-C Syntax
Use modern Objective-C syntax features like literals for NSArray, NSDictionary, and NSNumber, subscripting for collections, and boxed expressions. These make your code more concise, readable, and less error-prone.
Massive View Controllers
Avoid creating massive view controllers that handle too many responsibilities. Use patterns like MVVM (Model-View-ViewModel), MVP (Model-View-Presenter), or VIPER to separate concerns and make your code more modular, testable, and maintainable.
Not Using Blocks for Asynchronous Operations
Use blocks (closures) for asynchronous callbacks instead of delegate patterns for simple operations. Blocks make the code more concise and keep related code together, improving readability and maintainability.
Not Using Designated Initializers
Use the designated initializer pattern to ensure proper object initialization. Have one primary initializer that all other initializers call. This ensures consistent initialization and makes your code more maintainable.
Not Using Class Extensions for Private Methods
Use class extensions (anonymous categories) in implementation files to declare private methods and properties. This keeps your public interface clean and focused on what clients of your class need to know, while hiding implementation details.
Not Using Nullability Annotations
Use nullability annotations (nullable
, nonnull
, null_unspecified
, null_resettable
) to clarify whether properties and method parameters/return values can be nil. This improves code clarity, enables better Swift interoperability, and helps catch nil-related bugs at compile time.
Not Using Lightweight Generics
Use lightweight generics for collection types (NSArray, NSDictionary, NSSet) to specify the types they contain. This improves type checking, enables better autocompletion, and makes your code more self-documenting.
Not Using Categories and Extensions Appropriately
Use categories and extensions appropriately. Use categories to add methods to existing classes without subclassing. Keep core functionality in the main class, and use categories for grouping related utility methods. Be aware that categories cannot add instance variables (only properties backed by associative references).
Not Using Enumerations for Constants
Use NS_ENUM
or NS_OPTIONS
for enumerated constants instead of #define or global constants. Enumerations provide type safety, better autocompletion, and make your code more readable and maintainable.
Not Using instancetype for Initializers
Use instancetype
instead of id
as the return type for initializers and factory methods. This provides better type checking and enables the compiler to know the actual return type, improving autocompletion and catching errors at compile time.
Not Using Appropriate Memory Management Semantics
Use appropriate memory management semantics for properties. Use copy
for immutable objects like NSString to prevent unexpected changes, weak
for delegates and other references that shouldn’t own the object, and expose mutable collections as readonly with private mutable versions.
Not Using Appropriate Error Handling
Use appropriate error handling mechanisms. For methods that can fail, use the NSError pattern (taking an NSError** parameter) to provide detailed error information. This allows callers to understand why an operation failed and take appropriate action.
Not Using Appropriate Concurrency Patterns
Use appropriate concurrency patterns. Don’t block the main thread with long-running operations. Use Grand Central Dispatch (GCD) or NSOperationQueue for concurrent operations. Always update the UI on the main thread. Consider using higher-level abstractions like NSURLSession for network operations.
Not Using Proper Documentation
Use proper documentation for your classes and methods. Include information about parameters, return values, exceptions, and any side effects. Good documentation makes your code more maintainable and easier for others (and your future self) to understand and use correctly.
Not Using Appropriate Testing Patterns
Use appropriate testing patterns like dependency injection to make your code testable. Avoid singletons or provide a way to inject dependencies. Write code that can be easily mocked and tested in isolation.