Object C 语法入门

https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html

Class Defines

@interface SimpleClass : NSObject

{

NSString *_myNonPropertyInstanceVariable;

}

@end

Properties

@interface Person : NSObject

atomic原子，多线程保护

@property (readonly is readwrite getter=isFinished atomic nonatomic strong(默认) weak copy) NSString *firstName; (内部用_firstName存储）

@property NSString *lastName;

@end

@implement Person

{

NSString *_anotherCustomInstanceVariable;//不想公开

}

//没有下面这句，就默认是@synthesize propertyName = _propertyName

@synthesize propertyName = instanceVariableName;（指定存储值）

@end

init方法

- (id)init {

self = [super init];

if (self) {
// initialize instance variables here
}

return self;

}

实例方法

- (XYZObject *)someImportantObject {

if (!_someImportantObject) {

_someImportantObject = [[XYZObject alloc] init];

}

return _someImportantObject;

}

类方法

+ (XYZObject *)someImportantObject {

if (!_someImportantObject) {

_someImportantObject = [[XYZObject alloc] init];

}

return _someImportantObject;

}

strong 修饰的属性会在赋值时调用被指向对象的 retain 方法，导致其引用计数加1 。weak 则不会。另外还有个 unsafe_unretained，跟 weak 类似，区别是被指向对象消失时不会“自动“变成 nil 。

NSString *someString = @"Hello, World!";

NSNumber *myBOOL = @YES;
NSNumber *myFloat = @3.14f;
NSNumber *myInt = @42;
NSNumber *myLong = @42L;

不需要强类型

运行时报错

id someObject = @”Hello, World!”;

[someObject removeAllObjects];

编译时报错

NSString *someObject = @”Hello, World!”;

[someObject removeAllObjects];

if ([firstPerson isEqual:secondPerson]) {
// firstPerson is identical to secondPerson
}

if ([someDate compare:anotherDate] == NSOrderedAscending) {
// someDate is earlier than anotherDate
}

XYZPerson *somePerson;(会自动=nil)
// somePerson is automatically set to nil

属性自动会synthesize，需要定制才需要显式synthesize

get方法同属性名

set方法在属性名前面加set大写

[object valueForKey:(NSString*)]可以通过属性名来访问属性值

属性对应的变量名前面加了下划线_

@synthesize firstName; 变量同属性名

//下面是默认实习，有没有都一样

@synthesize firstName ＝ _firstName

-(id)init

{

self = [super init];

}

(void)dealloc {

NSLog(@”XYZPerson is being deallocated”);

}

//分类，主要用来实现私有。可以在.m中用category

@interface ClassName (CategoryName)

@end

@implementation XYZPerson (XYZPersonNameDisplayAdditions)

- (NSString *)lastNameFirstNameString {

return [NSString stringWithFormat:@”%@, %@”, self.lastName, self.firstName];

}

@end

Category

用于给class及其subclass添加新的方法

有自己单独的 .h 和 .m 文件

用于添加新方法，而不能添加新属性（property）

Extension

Extension常被称为是匿名的Category

用于给类添加新方法，但只作用于原始类，不作用于subclass

只能对有implementation源代码的类写Extension，对于没有implementation源代码的类，比如framework class，是不可以的

Extension可以给原始类添加新方法，以及新属性

@interface XYZPerson : NSObject

…

@property (readonly) NSString *uniqueIdentifier;

- (void)assignUniqueIdentifier;

@end

//下面隐藏信息，只有调用着才能调用、看到。需要源码实现。

@interface XYZPerson ()

@property (readwrite) NSString *uniqueIdentifier;

@end

@implementation XYZPerson

…

@end

Protocols有点像接口声明

@protocol XYZPieChartViewDataSource

@require

- (NSUInteger)numberOfSegments;

- (CGFloat)sizeOfSegmentAtIndex:(NSUInteger)segmentIndex;

@optional

- (NSString *)titleForSegmentAtIndex:(NSUInteger)segmentIndex;

@end

@protocol XYZPieChartViewDataSource

- (NSUInteger)numberOfSegments;

- (CGFloat)sizeOfSegmentAtIndex:(NSUInteger)segmentIndex;

@optional

- (NSString *)titleForSegmentAtIndex:(NSUInteger)segmentIndex;

@end

if ([self.dataSource respondsToSelector:@selector(titleForSegmentAtIndex:)]) {
thisSegmentTitle = [self.dataSource titleForSegmentAtIndex:index];
}

//接口（协议）继承

@protocol MyProtocol

…

@end

//实现借口

@interface MyClass : NSObject

…

@end

@interface MyClass : NSObject