runtime關聯屬性

關聯API介紹

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咱們先看看關聯API，只有這三個API，使用也是很是簡單的：

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/** * 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 */ void objc_setAssociatedObject ( id object , const void *key , id value , objc_AssociationPolicy policy )   /** * 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 */ id objc_getAssociatedObject ( id object , const void *key )   /** * 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 */ void objc_removeAssociatedObjects ( id object )

實際上，咱們幾乎不會使用到objc_removeAssociatedObjects函數，這個函數的功能是移除指定的對象上全部的關聯。

設置關聯值

對於設置關聯，咱們須要使用下面的API關聯起來：

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void objc_setAssociatedObject ( id object , const void *key , id value , objc_AssociationPolicy policy )

參數說明：

• object：與誰關聯，一般是傳self
• key：惟一鍵，在獲取值時經過該鍵獲取，一般是使用static const void *來聲明
• value：關聯所設置的值
• policy：內存管理策略，好比使用copy

獲取關聯值

若是咱們要獲取所關聯的值，須要經過key來獲取，調用以下函數：

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id objc_getAssociatedObject ( id object , const void *key )

參數說明：

• object：與誰關聯，一般是傳self，在設置關聯時所指定的與哪一個對象關聯的那個對象
• key：惟一鍵，在設置關聯時所指定的鍵

關聯策略

咱們先看看設置關聯時所指定的policy，它是一個枚舉類型，看官方說明：

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/** * Policies related to associative references. * These are options to objc_setAssociatedObject() */ typedef OBJC_ENUM ( uintptr_t , objc_AssociationPolicy ) {      OBJC_ASSOCIATION_ASSIGN = 0 ,            /**< Specifies a weak reference to the associated object. */      OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1 , /**< Specifies a strong reference to the associated object.                                             *   The association is not made atomically. */      OBJC_ASSOCIATION_COPY_NONATOMIC = 3 ,    /**< Specifies that the associated object is copied.                                             *   The association is not made atomically. */      OBJC_ASSOCIATION_RETAIN = 01401 ,        /**< Specifies a strong reference to the associated object.                                             *   The association is made atomically. */      OBJC_ASSOCIATION_COPY = 01403            /**< Specifies that the associated object is copied.                                             *   The association is made atomically. */ } ;

咱們說明一下各個值的做用：

• OBJCASSOCIATIONASSIGN：表示弱引用關聯，一般是基本數據類型，如int、float
• OBJCASSOCIATIONRETAIN_NONATOMIC：表示強（strong）引用關聯對象
• OBJCASSOCIATIONCOPY_NONATOMIC：表示關聯對象copy
• OBJCASSOCIATIONRETAIN：表示強（strong）引用關聯對象，但不是線程安全的
• OBJCASSOCIATIONCOPY：表示關聯對象copy，但不是線程安全的

擴展屬性

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咱們來寫一個例子，擴展UIControl添加Block版本的TouchUpInside事件。

擴展頭文件聲明：

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#import <UIKit/UIKit.h>   typedef void ( ^ HYBTouchUpBlock ) ( id sender ) ;   @interface UIControl ( HYBBlock )   @property ( nonatomic , copy ) HYBTouchUpBlock hyb_touchUpBlock ;   @end

擴展實現文件：

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#import "UIControl+HYBBlock.h" #import <objc/runtime.h>   static const void *sHYBUIControlTouchUpEventBlockKey = "sHYBUIControlTouchUpEventBlockKey" ;   @implementation UIControl ( HYBBlock )   - ( void ) setHyb_touchUpBlock : ( HYBTouchUpBlock ) hyb _ touchUpBlock {    objc_setAssociatedObject ( self ,                            sHYBUIControlTouchUpEventBlockKey ,                            hyb_touchUpBlock ,                            OBJC_ASSOCIATION_COPY ) ;       [ self removeTarget :self               action : @selector ( hybOnTouchUp : )     forControlEvents :UIControlEventTouchUpInside ] ;       if ( hyb_touchUpBlock ) {      [ self addTarget :self              action : @selector ( hybOnTouchUp : )    forControlEvents :UIControlEventTouchUpInside ] ;    } }   - ( HYBTouchUpBlock ) hyb _ touchUpBlock {    return objc_getAssociatedObject ( self , sHYBUIControlTouchUpEventBlockKey ) ; }   - ( void ) hybOnTouchUp : ( UIButton * ) sender {    HYBTouchUpBlock touchUp = self . hyb_touchUpBlock ;       if ( touchUp ) {      touchUp ( sender ) ;    } }   @end

使用起來很簡單吧！！！

用法，在使用到的類進行 引用category；

   

UIButton *backBtn = [UIButton buttonWithType:UIButtonTypeCustom];

    [backBtn setHyb_touchUpBlock:^(id btn){

        NSLog(@"backk");

    }];

就這樣愉快的使用啦