objc_setAssociatedObject/objc_getAssociatedObject

最新推荐文章于 2018-04-04 15:15:58 发布

LuohanCC

最新推荐文章于 2018-04-04 15:15:58 发布

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分类专栏： IOS应用开发文章标签： objc_setAssociatedOb associative

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本文介绍Objective-C中的关联对象机制，包括objc_setAssociatedObject、objc_getAssociatedObject和objc_removeAssociatedObjects三个方法。通过实例展示了如何利用该机制为UIView关联额外视图组件。

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IOS objc_setAssociatedObject/objc_getAssociatedObject

category和associative是objective-c的两个扩展机制，category就不介绍了，最常用也就是它。associative是一种发生在运行时的对象关联机制(引入 objc/runtime.h)，将一个对象关联到另一对象，通过一个关键字建立关联，这个关键词必须是唯一的，一般采用静态字符串变量才作为关键字。

associative机制共有3个方法，设置关联对象、获取关联对象、删除关联：

*源对象

*关键字:静态变量,可使用static const *NSString 或 staticchar

*关联的对象

*关联策略:assign，retain，copy等协议

OBJC_EXPORTvoid objc_setAssociatedObject(id object,constvoid *key,id value,objc_AssociationPolicy policy)

OBJC_EXPORTid objc_getAssociatedObject(id object,constvoid *key)

//Removes all associations for a given object.

OBJC_EXPORTvoid objc_removeAssociatedObjects(id object)

通过一个例子来展示associative的用法：

UIView+NodataView.h

// UIView+NodataView.h

// NewIOSProject
//
// Created by 罗函 on 16/7/5.
// Copyright © 2016年罗函. All rights reserved.

#import<UIKit/UIKit.h>

@interface UIView (NodataView)
- (void)addnodataView:(UIImage *)image text:(NSString *)text hint:(NSString *)hint toppadding:(double)toppadding;
- (void)removenodataView;

@end

UIView+NodataView.m

#import"UIView+NodataView.h"
#import <objc/runtime.h>

staticchar ERROR_IMAGE;
staticchar ERROR_LABEL;
staticchar ERROR_HINT;
@implementation UIView (NodataView)

- (void)setErrorimageview:(UIImageView *)errorimageview {
objc_setAssociatedObject(self, &ERROR_IMAGE, errorimageview,OBJC_ASSOCIATION_RETAIN_NONATOMIC);

}

- (UIImageView *)errorimageview {
returnobjc_getAssociatedObject(self, &ERROR_IMAGE);

}

- (void)setErrorlabel:(UILabel *)errorlabel {
objc_setAssociatedObject(self, &ERROR_LABEL, errorlabel,OBJC_ASSOCIATION_RETAIN_NONATOMIC);

}

- (UILabel *)errorlabel {
returnobjc_getAssociatedObject(self, &ERROR_LABEL);

}

- (void)setHintlabel:(UILabel *)hintlabel {
objc_setAssociatedObject(self, &ERROR_HINT, hintlabel,OBJC_ASSOCIATION_RETAIN_NONATOMIC);

}

- (UILabel *)hintlabel {
    returnobjc_getAssociatedObject(self, &ERROR_HINT);
}

- (void)addnodataView:(UIImage *)image text:(NSString *)text hint:(NSString *)hint toppadding:(double)toppadding{
    if(!self.errorimageview || !self.errorlabel) {
        double imagewidth =86.0;
        double labelheight =30.0;
        double hintheight =20.0;
        CGPoint center = [UIApplicationsharedApplication].delegate.window.center;
        center.y -= (toppadding + imagewidth/2);

        self.errorimageview = [[UIImageViewalloc]initWithFrame:CGRectMake(0,0, imagewidth, imagewidth)];
        self.errorimageview.center = center;
        [selfaddSubview:self.errorimageview];

        self.errorlabel = [[UILabelalloc]initWithFrame:CGRectMake(0,self.errorimageview.frame.origin.y+self.errorimageview.frame.size.height,self.bounds.size.width, labelheight)];
        [selfaddSubview:self.errorlabel];

        self.hintlabel = [[UILabelalloc]initWithFrame:CGRectMake(0,self.errorlabel.frame.origin.y+self.errorlabel.frame.size.height,self.bounds.size.width, hintheight)];
        [selfaddSubview:self.hintlabel];
        //setup
        self.errorlabel.font = [UIFontsystemFontOfSize:14.f];
        self.errorlabel.textColor = [UIColorcolorWithRed:0green:0blue:0alpha:0.4];
        self.errorlabel.textAlignment = NSTextAlignmentCenter;self.errorlabel.font = [UIFontsystemFontOfSize:13.f];
        self.hintlabel.font = [UIFontsystemFontOfSize:12.f];
        self.hintlabel.textColor = [UIColorcolorWithRed:0green:0blue:0alpha:0.2];
        self.hintlabel.textAlignment = NSTextAlignmentCenter;
    }
    [self.errorimageviewsetImage:image];
    [self.errorlabelsetText:text];
    [self.hintlabelsetText:hint];
}

- (void)removenodataView {
    if(self.errorimageview || self.errorlabel ||self.hintlabel) {
        [self.errorimageviewremoveFromSuperview];
        [self.errorlabelremoveFromSuperview];
        [self.hintlabelremoveFromSuperview];
        self.errorimageview =nil;
        self.errorlabel =nil;
        self.hintlabel =nil;
    }

}

@end