objective-C 的OOP(上)–類定義、繼承及方法調用

上一篇展示了如何用傳統的“面向過程編程方法”，實現畫“矩形”、“圓”、“橢圓”，這一篇看下如何改用OOP的方法來實現：

因為要用到“顏色”以及“矩形地區”二個枚舉，先把他們抽出來單獨放在CommDef.h檔案中

//定義“幾何形狀顏色”枚舉typedef enum{kRedColor,kGreenColor,kBlueColor} ShapeColor;//定義“幾何形狀矩形地區”結構typedef struct{int x,y,width,height;} ShapeRect;

然後再定義基類Shape，注意：在obj-C中，定義一個類通常分成二部分，一部分是".h"的檔案，用來申明類有哪些成員（也稱為類的定義檔案，類似於介面），另一部分是".m"的檔案，用來提供具體實現

Shape類的申明部分如下:(Shape.h)

////  Shape.h//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "CommDef.h"@interface Shape : NSObject {ShapeColor fillColor;ShapeRect bounds;}- (void) setFillColor:(ShapeColor) fillColor;- (void) setBounds:(ShapeRect) bounds;- (void) draw;- (NSString*) getColorName:(ShapeColor) fillColor;@end //Shape

Shape類的實現部分如下:(Shape.m)

////  Shape.m//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "Shape.h"@implementation Shape- (void) setBounds:(ShapeRect)b{bounds = b;}- (void) setFillColor:(ShapeColor)f{fillColor =f;}//註：這個方法留給子類去實現，所以這裡只要一個空殼就行了- (void) draw{}- (NSString*) getColorName:(ShapeColor)f{switch (f) {case kRedColor:return @"red";break;case kGreenColor:return @"green";break; case kBlueColor:return @"blue";break; default:return @"no clue";break;}}@end

文法有點奇怪，初次接觸，只能強迫自己忘記吧。

然後定義子類Circle

申明部分Circle.h

////  Circle.h//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "Shape.h"//註：因為Circle類不需要擴充其它方法，所以這裡也只要一個空殼@interface Circle : Shape {}@end

實現部分Circle.m

////  Circle.m//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "Circle.h"@implementation Circle-(void) draw{NSLog(@"drawing a Cirle at (%d,%d,%d,%d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,[super getColorName:fillColor]);}@end

註：上面展示了在obj-C中如何調用父類的方法[super getColorName:fillColor]

子類Rectangle

////  Rectangle.h//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "Shape.h"@interface Rectangle : Shape {}@end

實現部分

////  Rectangle.m//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "Rectangle.h"@implementation Rectangle-(void) draw{NSLog(@"drawing a Rectangle at (%d,%d,%d,%d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,[super getColorName:fillColor]);}@end

子類Ellipse

////  Ellipse.h//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "Shape.h"@interface Ellipse : Shape{}@end

實現部分

////  Ellipse.m//  HelloWorld////  Created by jimmy.yang on 11-1-26.//  Copyright 2011 __MyCompanyName__. All rights reserved.//#import "Ellipse.h"@implementation Ellipse-(void) draw{NSLog(@"drawing a ellipse at (%d,%d,%d,%d) in %@",bounds.x,bounds.y,bounds.width,bounds.height,[super getColorName:fillColor]);}@end

最後看下調用的主函數HelloWorld.m

#import "CommDef.h"#import "Circle.h"#import "Rectangle.h"#import "Ellipse.h"int main (int argc, const char * argv[]) {    id shape[2] ;ShapeRect rect0 =  {0,0,10,30};shape[0] = [Circle new];[shape[0] setBounds:rect0];[shape[0] setFillColor:kGreenColor];[shape[0] draw];ShapeRect rect1 =  {0,0,40,50};shape[1] = [Rectangle new];[shape[1] setBounds:rect1];[shape[1] setFillColor:kRedColor];[shape[1] draw];ShapeRect rect2 =  {0,0,30,30};shape[2] = [Ellipse new];[shape[2] setBounds:rect2];[shape[2] setFillColor:kBlueColor];[shape[2] draw];    return 0;}

註：上面的代碼中有一個id的變數，在obj-C中id相當於“任意類型”，意為指向某對象的指標（哪怕你不知道這個對象是什麼類型），總之，如果你不知道某對象的具體類型時，用它就對了。同時我們也看到了，建立一個類的執行個體用“[類 new]”來完成。

最後附上檔案結構圖: