Objective-c 學習筆記(二)

標籤：物件導向編程   xcode   objective-c   iphone   

物件導向編程（一）

面向過程編程

c語言便是一種面向過程編程的語言。舉一段程式碼來更加深刻的認識面向過程。

繪製集合圖形：

////  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;}

程式的運行結果是這樣的：

下面來分析這些函數：

首先用枚舉指定了幾種可以繪製的形狀

typedef enum {    circle,    rectangle,    egg} ShapeType;

接著是枚舉幾種可填充的顏色

typedef enum {    redColor,    greenColor,    blueColor} ShapeColor;

然後我們來設定要繪製的地區

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

最後用一個結構體將前面的內容結合起來，整體地描述一個形狀

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

接下來就是在main()函數中聲明三種形狀以及三種形狀地各種屬性值。

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()函數中調用了drawShapes()函數，用來繪製圖形。

drawShapes()函數線迴圈檢查每個數組中地Shape結構體，再用switch查看type欄位並且調用適當的函數繪製圖形。

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;        }    }}

此時，又調用了drawCircle(),drawRect(),drawEgg三個函數，這些函數需要輸出圖形資訊以及傳遞給它地顏色。

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()中又調用了colorName()函數，此函數負責轉換傳入地顏色值，並且返回NSString值。

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

這樣子看起來很簡單，也很顯而易見。不過維護起來就有些難度了。比如我要加上一個drawTriangle()來繪製三角形，那麼所有的函數基本上都要修改，而且有時還容易搞混。那麼OOP就可以用來解決這些問題。