Objective-C 语法一（类）

首先申明下，本文为笔者学习《Objective-C 基础教程》的笔记，并加入笔者自己的理解和归纳总结。

1、#import语句

#import可保证头文件只被包含一次。

#import <Foundation/Foundation.h>

2、NSLog和@"字符串"

NSLog方法与printf相似，向控制台输出。
@符号表示NSString类型。

3、布尔类型(BOOL)

YES和NO

4、类

@interface表示这是类的接口，以@end结束。
@implementation实现类定义的接口，以@end结束。
每个类都是NSObject。
在{}内定义类需要的各种数据成员。
短线"-"声明是类方法，后面紧跟返回类型，void表示无返回值。
方法参数中()定义参数类型，紧跟参数名。

@interface ShapeBounds : NSObject {int width, height;}- (void) setWidth: (int)width height: (int)height;@end@implementation ShapeBounds- (void) setWidth: (int)w height: (int)h {width = w;height = h;}- (NSString*) description {return [NSString stringWithFormat: @"(%d, %d)", width, height];}@endint main(int argc, const char* argv[]) {ShapeBounds* bounds = [ShapeBounds new];[bounds setWidth: 100 height: 60];NSLog(@"%@", bounds); // (100, 60)}

5、继承

类声明时，冒号":"后面的标识符是需要继承的类，Objective-C只支持单继承。
super关键字能调用父类的方法。

@interface Shape : NSObject - (void) draw;@end@implementation Shape- (void) draw {NSLog(@"draw Shape");}@end@interface Circle : Shape@end@implementation Circle- (void) draw {[super draw];NSLog(@"draw Circle");}@endint main(int argc, const char* argv[]) {Circle* circle = [Circle new];[circle draw];}

6、复合

Shape拥有自己的位置，可以用ShapeBounds表示。

@interface Shape : NSObject {ShapeBounds* bounds;}- (void) setBounds: (ShapeBounds*) bounds;- (void) draw;@end@implementation Shape- (void) setBounds: (ShapeBounds*) b {bounds = b;}- (void) draw {NSLog(@"draw Shape at %@", bounds);}@endint main(int argc, const char* argv[]) {ShapeBounds* bounds = [ShapeBounds new];[bounds setWidth: 100 height: 60];Circle* circle = [Circle new];[circle setBounds: bounds];[circle draw];}

7、跨文件依赖

ShapeBounds可以拆分为ShapeBounds.h和ShapeBounds.m
ShapeBounds.h文件

#import <Foundation/Foundation.h>@interface ShapeBounds : NSObject {int width, height;}- (void) setWidth: (int)Width height: (int)height;@end

ShapeBounds.m文件

#import "ShapeBounds.h"@implementation ShapeBounds- (void) setWidth: (int)w height: (int)h {width = w;height = h;}- (NSString*) description {return [NSString stringWithFormat: @"(%d, %d)", width, height];}@end

Shape类分为Shape.h和Shape.m，在Shape中引用了ShapeBounds类，必须在文件中声明依赖关系。
@class可以声明引用关系，在编译时知道这是一个类，但ShapeBounds被修改时不用重新编译Shape.h文件。
Shape.h文件

#import <Foundation/Foundation.h>@class ShapeBounds;@interface Shape : NSObject {ShapeBounds* bounds;}- (void) setBounds: (ShapeBounds*) bounds;- (void) draw;@end

Shape.m文件

#import "Shape.h"#import "ShapeBounds.h"@implementation Shape- (void) setBounds: (ShapeBounds*) b {bounds = b;}- (void) draw {NSLog(@"draw Shape at %@", bounds);}@end

Circle类分为Circle.h和Circle.m，Circle.h文件中Shape类不能用@class声明。
Circle.h文件

#import "Shape.h"@interface Circle : Shape@end

Circle.m文件

#import "Circle.h"@implementation Circle- (void) draw {[super draw];NSLog(@"draw Circle");}@end

main.m文件

#import "Circle.h"#import "ShapeBounds.h"int main(int argc, const char* argv[]) {ShapeBounds* bounds = [ShapeBounds new];[bounds setWidth: 100 height: 60];Circle* circle = [Circle new];[circle setBounds: bounds];[circle draw];}