我遇到的问题是我怀疑在Objective-C中如何使用指针和引用时的基本错误。我一直在关注这个问题，调整我的代码等等......但无济于事。
我知道我在某个地方犯了一个简单的错误（Objective-C的新手，但不是OOP）但是我没有看到它... argh：P
我欢迎你们自己提出的任何和所有的意见。 ：）
如果我可以说明我的问题，那就是这样的：
在我的“main.m”文件中，我实例化了某个“Rectangle”类的4个独立实例，每个类都有唯一的维度，并且可以通过getter（s）/ setter（s）访问笛卡尔坐标。 “width”和“height”属性是合成的，而坐标包含在可通过自定义方法访问的对象（XYPpoint类）中。
当我访问宽度和高度属性时，我能够为任何和所有实例获取/设置唯一值，但是当我尝试使用坐标时，我不可避免地会同时为所有实例更改它们。
我做错了什么？我可以看到我的原始对象只实例化了1（而不是4个tmes），但我不明白为什么？！？
* * *编辑： 根据hamstergene的善意建议（参见第一个答案）我再次尝试并通过声明* origin作为@property来使其工作。然而，我还必须先@synthesize它，然后在@implementation中覆盖它。我不知道为什么，但这对我来说似乎有些过分。这是正确的方法吗？此外，Xcode似乎不喜欢它并抛出警报（尽管仍在编译）
至于这里的代码是（短）：
=============================================== ===================================
// XYPoint.h
//
#import <Foundation/Foundation.h>
@interface XYPoint : NSObject
@property float x, y;
-(void) setX: (float) xVal andY: (float) yVal;
@end
=============================================== ===================================
// XYPoint.m
//
#import "XYPoint.h"
@implementation XYPoint
@synthesize x, y;
-(void) setX: (float) xVal andY: (float) yVal {
x = xVal;
y = yVal;
}
@end
=============================================== ===================================
// Rectangle.h
//
#import <Foundation/Foundation.h>
#import "XYPoint.h"
@interface Rectangle : NSObject
@property float width,
height;
-(XYPoint *) origin;
-(void) setWidth: (float) w andHeight: (float) h;
-(void) setOrigin: (XYPoint *) pt;
-(void) printData;
@end
=============================================== ===================================
// Rectangle.m
//
#import "Rectangle.h"
@implementation Rectangle
@synthesize width, height;
XYPoint *origin;
-(void) setWidth:(float) w andHeight: (float) h {
width = w;
height = h;
}
-(XYPoint *) origin {
return origin;
}
-(void) setOrigin: (XYPoint *) pt {
if ( ! origin ) {
NSLog( @"origin object created" );
origin = [ [ XYPoint alloc ] init ];
}
origin.x = pt.x;
origin.y = pt.y;
}
-(void) printData {
NSLog( @"origin coordinates ( %.1f, %.1f )", origin.x, origin.y );
NSLog( @"Width = %.1f, Height = %.1f\n" );
}
@end
=============================================== ===================================
// main.m
//
#import "Rectangle.h"
int main(int argc, const char * argv[]) {
@autoreleasepool {
XYPoint *rect1Origin = [ [ XYPoint alloc ] init ];
XYPoint *rect2Origin = [ [ XYPoint alloc ] init ];
XYPoint *rect3Origin = [ [ XYPoint alloc ] init ];
XYPoint *rect4Origin = [ [ XYPoint alloc ] init ];
Rectangle *rect1 = [ [ Rectangle alloc ] init ];
Rectangle *rect2 = [ [ Rectangle alloc ] init ];
Rectangle *rect3 = [ [ Rectangle alloc ] init ];
Rectangle *rect4 = [ [ Rectangle alloc ] init ];
[ rect1Origin setX: 200 andY: 420 ];
[ rect1 setOrigin: rect1Origin ];
[ rect1 setWidth: 250 andHeight: 75 ];
NSLog( @"1st Rectangle\n------------------------------------------" );
[ rect1 printData ];
[ rect2Origin setX: 400 andY: 300 ];
[ rect2 setOrigin: rect2Origin ];
[ rect2 setWidth: 100 andHeight: 180 ];
NSLog( @"2nd Rectangle\n------------------------------------------" );
[ rect2 printData ];
[ rect3Origin setX: 99 andY: 99 ];
[ rect3 setOrigin: rect3Origin ];
[ rect3 setWidth: 50 andHeight: 450 ];
NSLog( @"3rd Rectangle\n------------------------------------------" );
[ rect3 printData ];
[ rect4Origin setX: 20 andY: 100 ];
[ rect4 setOrigin: rect4Origin ];
[ rect4 setWidth: 10 andHeight: 3 ];
NSLog( @"4th Rectangle\n------------------------------------------" );
[ rect4 printData ];
NSLog( @"\n------------------------------------------" );
NSLog( @"1st Rectangle again...\n------------------------------------------" );
[ rect1 printData ];
NSLog( @"2nd Rectangle again...\n------------------------------------------" );
[ rect2 printData ];
NSLog( @"3rd Rectangle again...\n------------------------------------------" );
[ rect3 printData ];
NSLog( @"4th Rectangle again...\n------------------------------------------" );
[ rect4 printData ];
NSLog( @"\n\n********* All rects have the same coordinates why does this happen?" );
}
return 0;
}
=============================================== ===================================
origin object created
1st Rectangle
------------------------------------------
origin coordinates ( 200.0, 420.0 )
Width = 250.0, Height = 75.0
2nd Rectangle
------------------------------------------
origin coordinates ( 400.0, 300.0 )
Width = 100.0, Height = 180.0
3rd Rectangle
------------------------------------------
origin coordinates ( 99.0, 99.0 )
Width = 50.0, Height = 450.0
4th Rectangle
------------------------------------------
origin coordinates ( 20.0, 100.0 )
Width = 10.0, Height = 3.0
------------------------------------------
1st Rectangle again...
------------------------------------------
origin coordinates ( 20.0, 100.0 )
Width = 250.0, Height = 75.0
2nd Rectangle again...
------------------------------------------
origin coordinates ( 20.0, 100.0 )
Width = 100.0, Height = 180.0
3rd Rectangle again...
------------------------------------------
origin coordinates ( 20.0, 100.0 )
Width = 50.0, Height = 450.0
4th Rectangle again...
------------------------------------------
origin coordinates ( 20.0, 100.0 )
Width = 10.0, Height = 3.0
********* All rects have the same coordinates why does this happen?
答案 0 :(得分：3)
XYPoint *origin;是一个全局变量，这意味着它在整个程序中共享。您需要将其声明为属性，就像使用x，y，width和height一样。
答案 1 :(得分：0)
我发现了我做错了什么。使用@ property / @ synthesize指令工作正常，但从技术上讲，问题是一个简单的语法问题，它改变了我的Rectangle.m实现中变量* origin的范围。
基本上我需要做的就是将变量声明包含在曲线引号之间（没有它们我无意中将* origin设置为全局。）
所以基本上不是这个：
//=======================================
@implementation Rectangle
//=======================================
@synthesize width, height;
XYPoint *origin;
我应该这样做：
//=======================================
@implementation Rectangle
//=======================================
{
XYPoint *origin;
}
@synthesize width, height;
Et voila' - 问题解决了。感谢David Todd（来自：http://classroomm.com/objective-c/index.php?topic=9389.0）寻求他的解决方案（再次来到hamstergene和rob mayoff）