iOS开发--开发细节（使用关联对象存取自定义数据）

关联对象可以给一个定义好的对象 增加一个KEY从而来存取自定义数据

提供了三个API

/** **设置** * Sets an associated value for a given object using a given key and association policy. *  * @param object The source object for the association. * @param key The key for the association. * @param value The value to associate with the key key for object. Pass nil to clear an existing association. * @param policy The policy for the association. For possible values, see “Associative Object Behaviors.” *  * @see objc_setAssociatedObject * @see objc_removeAssociatedObjects */OBJC_EXPORT void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)    __OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_1);/** **读取** * Returns the value associated with a given object for a given key. *  * @param object The source object for the association. * @param key The key for the association. *  * @return The value associated with the key \e key for \e object. *  * @see objc_setAssociatedObject */OBJC_EXPORT id objc_getAssociatedObject(id object, const void *key)    __OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_1);/** **删除** * Removes all associations for a given object. *  * @param object An object that maintains associated objects. *  * @note The main purpose of this function is to make it easy to return an object  *  to a "pristine state”. You should not use this function for general removal of *  associations from objects, since it also removes associations that other clients *  may have added to the object. Typically you should use \c objc_setAssociatedObject  *  with a nil value to clear an association. *  * @see objc_setAssociatedObject * @see objc_getAssociatedObject */OBJC_EXPORT void objc_removeAssociatedObjects(id object)    __OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_1);

objc_AssociationPOlicyen Enum

typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {    OBJC_ASSOCIATION_ASSIGN = 0,  //相当于属性中的assign             OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, //retain,monatomic    OBJC_ASSOCIATION_COPY_NONATOMIC = 3,  //copy,nonatomic    OBJC_ASSOCIATION_RETAIN = 01401,    //retain     OBJC_ASSOCIATION_COPY = 01403     //copy    };

Demo 给button 增加了一个string

#import "ViewController.h"#import <objc/runtime.h>static void * myBtnKey = "myBtnKey";@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.    UIButton *btn = [UIButton buttonWithType:UIButtonTypeSystem];    btn.backgroundColor = [UIColor blackColor];    btn.frame = CGRectMake(100, 100, 60, 30);    [self.view addSubview:btn];     objc_setAssociatedObject(btn, myBtnKey, @"mybtn", OBJC_ASSOCIATION_RETAIN_NONATOMIC);    [btn addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}- (void)btnClick:(id)sender {    NSString *str = objc_getAssociatedObject(sender, myBtnKey);    /**     *  CODE     */}