我找不出方法的區別

Question

@interface Rectangle: NSObject 
-(void) setOrigin : (XYPoint *) pt; 
-(XYPoint *) origin; 
... 
@end 

#import "XYPoint.h" 
#import "Rectangle.h" 
@implementation Rectangle 
-(void) setOrigin : (XYPoint *) pt 
{ 
    origin = pt; 
} 

-(XYPoint *) origin 
{ 
    return origin; 
} 
@end 

@interface XYPoint: NSObject 
@property int x, y; 
-(void) setX: (int) xVall andY; (int) yVal; 
@end 

#import "XYPoint.h" 
@implementation XYPoint 
@synthesize x, y 
-(void) setX: (int) xVal andY: (int) yVal 
{ 
    x = xVal; 
    y = yVal; 
} 
@end 

上面是類的一部分。 這是主要

int main (int argc, const char* argv[]) 
{ 
    XYPoint* myPoint = [[XYPoint alloc]init]; 
    Rectangle* myRect = [[Rectangle alloc]init]; 

    [myPoint setX: 200 andY: 100]; 

    [myRect setOrigin: myPoint]; 
    NSLog(@"origin of rectangle: (%i, %i)", myRect.origin.x, myRect.origin.y); 
    return 0; 
} 

這工作如我所料不錯。但是，如果我改變了方法

setOrigin: (XYPoint *) pt 

在Rectangle類，以

-(void) setOrigin: (XYPoint *) pt 
{ 
    origin.x = pt.x; 
    origin.y = pt.y; 
} 

它只是打印的0 x和y的值。這兩種方法有什麼區別。對我來說，似乎是一樣的。

Answer 1

我敢打賭你不知道alloc並在Rectangle類的初始化init你origin對象...