类别添加属性，即runtime运行时添加属性（动态属性）

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在自定义扩展类时，可以通过运行时添加属性。

关键点在于，首先必须导入运行时头文件；

#import <objc/runtime.h>

其次，设置属性；

objc_setAssociatedObject(self, &keyLineBottom, lineBottom, OBJC_ASSOCIATION_RETAIN);

还有是获得设置的属性；

UIImageView *lineBottom = objc_getAssociatedObject(self, &keyLineBottom);

还有一点需要设置，即设置关联key值

static NSString *const keyLineBottom = @"lineBottomView";

注意：扩展类中添加的属性必须是对象类型，如要添加NSInteger类型，则需转换成NSNumber类型。

示例如下（UITableViewCell添加底端分割线属性）:

.h文件

#import <UIKit/UIKit.h>@interface UITableViewCell (CellLine)///设置分割线- (void)showLineView:(CGFloat)offX color:(UIColor *)lineColor type:(CellLineShowType)type;///底端分割线@property (nonatomic, strong) UIImageView *lineViewButtom;@end

.m文件

#import "UITableViewCell+CellLine.h"#import <objc/runtime.h>static NSString *const keyLineTop = @"lineTopView";static NSString *const keyLineBottom = @"lineBottomView";static CGFloat const heightLine = 0.5; // 默认分割线高度@implementation UITableViewCell (CellLine)///设置分割线- (void)showLineView:(CGFloat)offX color:(UIColor *)lineColor type:(CellLineShowType)type{    // 底端分割线    UIImageView *lineBottom = objc_getAssociatedObject(self, &keyLineBottom);    if (!lineBottom)    {        lineBottom = [[UIImageView alloc] initWithFrame:CGRectMake(0.0, (CGRectGetHeight(self.bounds) - heightLine), CGRectGetWidth(self.bounds), heightLine)];        [self.contentView addSubview:lineBottom];                objc_setAssociatedObject(self, &keyLineBottom, lineBottom, OBJC_ASSOCIATION_RETAIN);    }    CGRect rectButtom = lineBottom.frame;    rectButtom.origin.x = offX;    lineBottom.frame = rectButtom;        lineBottom.backgroundColor = lineColor;    lineBottom.image = [UIImage imageWithColor:lineColor andSize:CGSizeMake(1.0, 1.0)];        // 顶端分割线    UIImageView *lineTop = objc_getAssociatedObject(self, &keyLineTop);    if (!lineTop)    {        lineTop = [[UIImageView alloc] initWithFrame:CGRectMake(0.0, 0.0, CGRectGetWidth(self.bounds), heightLine)];        [self.contentView addSubview:lineTop];                objc_setAssociatedObject(self, &keyLineTop, lineTop, OBJC_ASSOCIATION_RETAIN);    }        CGRect rectTop = lineTop.frame;    rectTop.origin.x = offX;    lineTop.frame = rectTop;        lineTop.backgroundColor = lineColor;    lineTop.image = [UIImage imageWithColor:lineColor andSize:CGSizeMake(1.0, 1.0)];        switch (type)    {        case CellLineShowNone:        {            lineBottom.hidden = YES;            lineTop.hidden = YES;        }            break;        case CellLineShowAll:        {            lineBottom.hidden = NO;            lineTop.hidden = NO;        }            break;        case CellLineShowButtom:        {            lineBottom.hidden = NO;            lineTop.hidden = YES;        }            break;        case CellLineShowTop:        {            lineBottom.hidden = YES;            lineTop.hidden = NO;        }            break;                    default:            break;    }}#pragma mark - setter/getter- (void)setLineViewButtom:(UIImageView *)lineViewButtom{    objc_setAssociatedObject(self, &keyLineBottom, lineViewButtom, OBJC_ASSOCIATION_RETAIN);}- (UIImageView *)lineViewButtom{    UIImageView *line = objc_getAssociatedObject(self, &keyLineBottom);    return line;}- (void)setLineViewTop:(UIImageView *)lineViewTop{    objc_setAssociatedObject(self, &keyLineTop, lineViewTop, OBJC_ASSOCIATION_RETAIN);}- (UIImageView *)lineViewTop{    UIImageView *line = objc_getAssociatedObject(self, &keyLineTop);    return line;}@end

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