Objective-c 学习笔记(二)

面向对象编程（一）

面向过程编程

c语言便是一种面向过程编程的语言。举一段程序代码来更加深刻的认识面向过程。

绘制集合图形：

//
//  main.m
//  oc
//
//  Created by Tron on 14-8-8.
//  Copyright (c) 2014年 Tron. All rights reserved.
//

#import <Foundation/Foundation.h>

typedef enum {
    circle,
    rectangle,
    egg
} ShapeType;

typedef enum {
    redColor,
    greenColor,
    blueColor
} ShapeColor;

typedef struct {
    int x,y,height,width;
} ShapeRect;

typedef struct {
    ShapeType type;
    ShapeColor color;
    ShapeRect boods;
} Shape;

NSString *colorName (ShapeColor color) {
    switch (color) {
        case redColor:
            return @"Red";
            break;
        case blueColor:
            return @"Blue";
            break;
        case greenColor:
            return @"Green";
            break;
    }
}

int drawCircle (ShapeRect boods,ShapeColor color) {
    NSLog(@"Draw a circle at (%d %d %d %d) in %@",boods.x,boods.y,boods.width,boods.height,colorName(color));
    return 0;
}

int drawEgg (ShapeRect boods,ShapeColor color) {
    NSLog(@"Draw a Egg at (%d %d %d %d) in %@",boods.x,boods.y,boods.width,boods.height,colorName(color));
    return 0;
}

int drawRect (ShapeRect boods,ShapeColor color) {
    NSLog(@"Draw a rectangle at (%d %d %d %d) in %@",boods.x,boods.y,boods.width,boods.height,colorName(color));
    return 0;
}

void drawShapes (Shape shapes[],int count) {
    for (int i=0;i<count;i++) {
        switch (shapes[i].type) {
            case circle:
                drawCircle (shapes[i].boods,shapes[i].color);
                break;
            case rectangle:
                drawRect (shapes[i].boods,shapes[i].color);
                break;
            case egg:
                drawEgg (shapes[i].boods,shapes[i].color);
                break;
        }
    }
}

int main(){
    Shape shapes[3];
    ShapeRect rect0 = {0,0,10,30};
    shapes[0].type = circle;
    shapes[0].color = redColor;
    shapes[0].boods = rect0;
    ShapeRect rect1 = {30,40,50,60};
    shapes[1].type = rectangle;
    shapes[1].color = greenColor;
    shapes[1].boods = rect1;
    ShapeRect rect2 = {15,18,37,29};
    shapes[2].type = egg;
    shapes[2].color = blueColor;
    shapes[2].boods = rect2;
    drawShapes(shapes, 3);
    return 0;
}

程序的运行结果是这样的：

下面来分析这些函数：

首先用枚举指定了几种可以绘制的形状

typedef enum {
    circle,
    rectangle,
    egg
} ShapeType;

接着是枚举几种可填充的颜色

typedef enum {
    redColor,
    greenColor,
    blueColor
} ShapeColor;

然后我们来设定要绘制的区域

typedef struct {
    int x,y,height,width;
} ShapeRect;

最后用一个结构体将前面的内容结合起来，整体地描述一个形状

typedef struct {
    ShapeType type;
    ShapeColor color;
    ShapeRect boods;
} Shape;

接下来就是在main()函数中声明三种形状以及三种形状地各种属性值。

int main(){
    Shape shapes[3];
    ShapeRect rect0 = {0,0,10,30};
    shapes[0].type = circle;
    shapes[0].color = redColor;
    shapes[0].boods = rect0;
    ShapeRect rect1 = {30,40,50,60};
    shapes[1].type = rectangle;
    shapes[1].color = greenColor;
    shapes[1].boods = rect1;
    ShapeRect rect2 = {15,18,37,29};
    shapes[2].type = egg;
    shapes[2].color = blueColor;
    shapes[2].boods = rect2;
    drawShapes(shapes, 3);
    return 0;
}

在main()函数中调用了drawShapes()函数，用来绘制图形。

drawShapes()函数线循环检查每个数组中地Shape结构体，再用switch查看type字段并且调用适当的函数绘制图形。

void drawShapes (Shape shapes[],int count) {
    for (int i=0;i<count;i++) {
        switch (shapes[i].type) {
            case circle:
                drawCircle (shapes[i].boods,shapes[i].color);
                break;
            case rectangle:
                drawRect (shapes[i].boods,shapes[i].color);
                break;
            case egg:
                drawEgg (shapes[i].boods,shapes[i].color);
                break;
        }
    }
}

此时，又调用了drawCircle(),drawRect(),drawEgg三个函数，这些函数需要输出形状信息以及传递给它地颜色。

int drawCircle (ShapeRect boods,ShapeColor color) {
    NSLog(@"Draw a circle at (%d %d %d %d) in %@",boods.x,boods.y,boods.width,boods.height,colorName(color));
    return 0;
}

int drawEgg (ShapeRect boods,ShapeColor color) {
    NSLog(@"Draw a Egg at (%d %d %d %d) in %@",boods.x,boods.y,boods.width,boods.height,colorName(color));
    return 0;
}

int drawRect (ShapeRect boods,ShapeColor color) {
    NSLog(@"Draw a rectangle at (%d %d %d %d) in %@",boods.x,boods.y,boods.width,boods.height,colorName(color));
    return 0;
}

然而在NSLog()中又调用了colorName()函数，此函数负责转换传入地颜色值，并且返回NSString值。

NSString *colorName (ShapeColor color) {
    switch (color) {
        case redColor:
            return @"Red";
            break;
        case blueColor:
            return @"Blue";
            break;
        case greenColor:
            return @"Green";
            break;
    }
}

这样子看起来很简单，也很显而易见。不过维护起来就有些难度了。比如我要加上一个drawTriangle()来绘制三角形，那么所有的函数基本上都要修改，而且有时还容易搞混。那么OOP就可以用来解决这些问题。

Objective-c 学习笔记(二)