类别动态添加属性(runtime知识点)

.h文件
#import <UIKit/UIKit.h>

@interface UIImage (Extension)

//起始x坐标
@property(nonatomic,assign)CGFloat imageX;

//起始y轴坐标
@property(nonatomic,assign)CGFloat imageY;


@end

.m文件
#import "UIImage+Extension.h"
#import <objc/runtime.h>

static const NSString *imageXKey = @"imageX";
static const NSString *imageYKey = @"imageY";

@implementation UIImage (Extension)

- (void)setImageX:(CGFloat)imageX {
    
    
    objc_setAssociatedObject(self, @selector(imageX), @(imageX), OBJC_ASSOCIATION_ASSIGN);
    
}

- (CGFloat)imageX {
    
    
    return [(objc_getAssociatedObject(self, @selector(imageX))) doubleValue];

}


- (void)setImageY:(CGFloat)imageY {
    
    
    objc_setAssociatedObject(self, &imageYKey, @(imageY), OBJC_ASSOCIATION_ASSIGN);
    
}

- (CGFloat)imageY {
    
    
    return [(objc_getAssociatedObject(self, &imageYKey)) doubleValue];
    
}

@end