1.过程式编程实例，画出Shape数组中的图形：
//// main.m// hello-obj//// Created by zhouyang on 16/4/4.// Copyright © zhouyang. All rights reserved.//#import <Foundation/Foundation.h>//枚举变量，代表形状typedef enum{kCircle,kRectangle,kEgg} ShapeType;//枚举变量，代表颜色typedef enum{kRedColor,kGreenColor,kBlueColor} ShapeColor;//结构体，代表形状typedef struct{int x,y,width,height;}ShapeRect;//结构体，表示多边形的各项属性typedef struct {ShapeType type;ShapeColor fillColor;ShapeRect bounds;}Shape;//返回颜色对应的NSStringNSString *colorName(ShapeColor colorName){switch(colorName){case kRedColor:return @"red";break;case kGreenColor:return @"green";break;case kBlueColor:return @"blue";break;}return @"no clue";}//“画出”圆，其实就是输出图形的各项属性void drawCircle(ShapeRect bounds,ShapeColor fillColor){NSLog(@"drawing a circle at (%d,%d,%d,%d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,colorName(fillColor));}//“画出”长方形void drawRectangle(ShapeRect bounds,ShapeColor fillColor){NSLog(@"drawing a rectangle at (%d,%d,%d,%d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,colorName(fillColor));}//"画出"Eggvoid drawEgg(ShapeRect bounds,ShapeColor fillColor){NSLog(@"drawing a egg at (%d,%d,%d,%d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,colorName(fillColor));}//遍历Shape数组，画出对应的图形void drawShapes(Shape shapes[],int count){for(int i=0;i<count;i++){switch (shapes[i].type) {case kCircle:drawCircle(shapes[i].bounds, shapes[i].fillColor);break;case kRectangle:drawRectangle(shapes[i].bounds,shapes[i].fillColor);break;case kEgg:drawEgg(shapes[i].bounds,shapes[i].fillColor);break;default:NSLog(@"can't find the shape!");}}}int main(int argc, const char * argv[]) {Shape shapes[3];//CircleShapeRect rect0={0,0,10,30};shapes[0].type=kCircle;shapes[0].fillColor=kRedColor;shapes[0].bounds=rect0;//RectangleShapeRect rect1={30,40,50,60};shapes[1].type=kRectangle;shapes[1].fillColor=kGreenColor;shapes[1].bounds=rect1;//EggShapeRect rect2={15,18,37,29};shapes[2].type=kEgg;shapes[2].fillColor=kBlueColor;shapes[2].bounds=rect2;//画出数组Shape中的图形drawShapes(shapes,3);}
基于OOP编程，可以将上述代码改写为以下格式：
#import <Foundation/Foundation.h>//注意枚举变量的定义，变量之间以逗号隔开typedef enum{kRedColor,kGreenColor,kBlueColor}ShapeColor;typedef struct {int x,y,width,height;}ShapeRect;NSString *ColorName(ShapeColor color){switch (color) {case kRedColor:return @"red";break;case kGreenColor:return @"green";break;case kBlueColor:return @"blue";break;}return @"no clue";}//定义接口//@告诉编译器，这里是对C的扩展@interface Circle:NSObject{//定义数据成员@privateShapeColor fillColor;ShapeRect bounds;}//列举方法的名称，返回值的类型和某些参数//前面的短线表明这是Objective-c方法的声明- (void) setFillColor:(ShapeColor) fillColor;- (void) setBounds:(ShapeRect) bounds;- (void) draw;@end //@Circle//接口定义完毕//下面开始实现接口Circle@implementation Circle- (void) setFillColor:(ShapeColor) c {fillColor=c;}//设置颜色- (void) setBounds:(ShapeRect) b{bounds=b;}- (void) draw{NSLog(@"drawing a circle at (%d %d %d %d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,ColorName(fillColor));}@end //Circle//定义接口//@告诉编译器，这里是对C的扩展@interface Rectangle:NSObject{//定义数据成员@privateShapeColor fillColor;ShapeRect bounds;}//列举方法的名称，返回值的类型和某些参数//前面的短线表明这是Objective-c方法的声明- (void) setFillColor:(ShapeColor) fillColor;- (void) setBounds:(ShapeRect) bounds;- (void) draw;@end //@Rectangle//接口定义完毕//下面开始实现接口Rectangle@implementation Rectangle- (void) setFillColor:(ShapeColor) c {fillColor=c;}//设置颜色- (void) setBounds:(ShapeRect) b{bounds=b;}- (void) draw{NSLog(@"drawing a rectangle at (%d %d %d %d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,ColorName(fillColor));}@end //Egg//定义接口//@告诉编译器，这里是对C的扩展@interface Egg:NSObject{//定义数据成员@privateShapeColor fillColor;ShapeRect bounds;}//列举方法的名称，返回值的类型和某些参数//前面的短线表明这是Objective-c方法的声明- (void) setFillColor:(ShapeColor) fillColor;- (void) setBounds:(ShapeRect) bounds;- (void) draw;@end //@Triangle//接口定义完毕//下面开始实现接口Triangle@implementation Egg- (void) setFillColor:(ShapeColor) c {fillColor=c;}//设置颜色- (void) setBounds:(ShapeRect) b{bounds=b;}- (void) draw{NSLog(@"drawing a egg at (%d %d %d %d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,ColorName(fillColor));}@end //Egg//定义接口//@告诉编译器，这里是对C的扩展@interface Triangle:NSObject{//定义数据成员@privateShapeColor fillColor;ShapeRect bounds;}//列举方法的名称，返回值的类型和某些参数//前面的短线表明这是Objective-c方法的声明- (void) setFillColor:(ShapeColor) fillColor;- (void) setBounds:(ShapeRect) bounds;- (void) draw;@end //@Triangle//接口定义完毕//下面开始实现接口Triangle@implementation Triangle- (void) setFillColor:(ShapeColor) c {fillColor=c;}//设置颜色- (void) setBounds:(ShapeRect) b{bounds=b;}- (void) draw{NSLog(@"drawing a triangle at (%d %d %d %d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,ColorName(fillColor));}@end //Triangle//画出图形//id 对应类实例void drawShapes(id shapes[],int count){for(int i=0;i<count;i++){id shape=shapes[i];[shape draw];}}int main(int argc, const char * argv[]) {id shapes[4];//Circleshapes[0]=[Circle new];//这里创建新的类实例将new加在类名称的后面ShapeRect rect0={0,0,10,30};[shapes[0] setBounds:rect0];[shapes[0] setFillColor:kRedColor];//RectangleShapeRect rect1={30,40,50,60};shapes[1] =[ Rectangle new];[shapes[1] setBounds:rect1];[shapes[1] setFillColor:kGreenColor];//EggShapeRect rect2={15,18,37,29};shapes[2] =[Egg new];[shapes[2] setBounds:rect2];[shapes[2] setFillColor:kBlueColor];//TriangleShapeRect rect3 ={47,32,80,50};shapes[3] =[Triangle new];[shapes[3] setBounds:rect3];[shapes[3] setFillColor:kGreenColor];//画出数组Shape中的图形drawShapes(shapes,4);return 0;}
可见利用OOP编程方式，增加新的图形更加简单，修改的地方更少。
请注意object-c中的接口，类的定义以及类方法的调用，这里与C++还是存在很多的不同。
可能会遇到错误：Must explicitly describe intended ownership of an object array parameter，解决方法如下：
将Objective-c Automatic Reference Counting 设置为No，关闭ARC即可。
