iOS Development--Project Combat Summary & Show you the essence of objective-c

I'll show you the essence of objective-c.

1: Interface and implementation

• @interface...@end
• @implementation...@end
• @class

Interface (header file)

Implementation file

Forward reference

Note: Categories extend the behavior of existing classes by adding new classes and instance methods. As a rule, categories are defined in their own .{h,m} files,

2: Instance variable visibility

• @public
• @package
• @protected
• @private

@public: Instance variables can person->age = 32" be read directly using symbols.

@package: instance variable is public unless it is specified outside the frame (64-bit schema only)

@protected: Instance variables can only be accessed by their classes and their derived classes

@private: Instance variables can only be accessed by their classes

3: Properties

• @property
• @synthesize
• @dynamic

One thing to note about attributes is that, starting with Xcode 4.4, we no longer need explicit compositing attributes. The @interface attributes declared in the implementation are automatically synthesized (along with the underlined Ivar name, for example @synthesize propertyName = _propertyName ).

@dynamic are relative to the @synthesize, they are used to modify the @property to generate the corresponding getter and setter methods. But @ dynamic means that the getter and setter methods of this member variable are not generated directly by the compiler, but are generated either manually or at run time.

4: Protocol

• @protocol
• @required
• @optional

Defines a set of methods that will be implemented in classes that obey the protocol, as if they were added to the interface of that class.

You can customize a protocol in more depth by specifying a method that is necessary and optional. The optional method is stub on the interface so that it can be completed automatically by Xcode but does not generate a warning if the method is not implemented. The protocol method is required by default

5: Exception Handling

• @try
• @catch
• @finally
• @throw

Objective-c mainly through NSError the communication of unexpected abnormal state. While other languages use exception handling, OBJECTIVE-C will downgrade exceptions and programmer errors to the behavior of true exceptions.

6: Object Constants

• @""
• @42, @3.14, @YES,@‘Z‘
• @[]
• @{}
• @()

@"": Returns an object that is initialized by the Unicode content in quotation marks NSString .

@42, @3.14 , @YES , @‘Z‘ : Returns an object that is initialized by a related class NSNumber , such as @42 → [NSNumber numberWithInteger:42] , or @YES → [NSNumber numberWithBool:YES] . Support for further specifying types using suffixes, such as @42U → [NSNumber numberWithUnsignedInt:42U] .

@[]: Returns an object with a colon-delimited list of objects as content NSArray . For example, @[@"A", @NO, @2.718] → [NSArray arrayWithObjects:@"A", @NO, @2.718, nil] (note that closing a tag in an array constant nil is not required).

@{}: Returns an object that is initialized as content by a specific key-value pair, in the NSDictionary format: @{@"someKey" : @"theValue"} .

@(): Dynamically evaluates encapsulated representations and returns appropriate object constants based on their values (for example, return, const char* NSString int return NSNumber , etc.). ）。 This is also 枚举 the specified way of using numeric constants and values.

7:objective-c Constants

• @selector()
• @protocol()

@selector(): Returns a pointer to a selector with a specific name SEL . Used -performSelector:withObject: in similar ways.

@protocol(): Returns a pointer to a protocol with a specific name Protocol * . Used -conformsToProtocol: in similar ways.

8:c Constants

• @encode()
• @defs()

@encode(): Returns the type encoding of a type. This type value can be used for NSCoder -encodeValueOfObjCType:at the first parameter encoding in.

@defs(): Returns the layout of a objective-c class. For example, to define a NSObject struct with the same layout, you only need this:

9: Optimization

• @autoreleasepool{}
• @synchronized{}

@autoreleasepool{}: If your code contains tight loops that create a lot of temporary objects, you can @autorelease optimize them by more aggressively releasing these short-lived, locally scoped objects. @autoreleasepoolReplace and improve the old and slow and cannot be used in Arc NSAutoreleasePool .

@synchronized(){}: This instruction self provides a convenient way to ensure that a particular block is safely executed in a particular environment. The deadlock in this case is expensive, so for classes that are thread-safe at a particular level, it is recommended to use a dedicated NSLock property or use OSAtomicCompareAndSwap32(3) the underlying deadlock function.

10: Compatible

• @compatibility_alias

Allows existing classes to have different names as aliases.

iOS Development--Project Combat Summary & Show you the essence of objective-c