iOS學習系列 - 擴展機制category與associative

category與associative作為objective-c的擴展機制的兩個特性，category即類型，可以通過它來擴展方法；associative，可以通過它來擴展屬性；在iOS開發中，可能category比較常見，相對的associative，就用的比較少，要用它必須使用<objc/runtime.h>的頭文件，然后就可以自由使用objc_getAssociatedObject以及objc_setAssociatedObject，我們來看下這兩個方法：

OBJC_EXPORT?void?objc_setAssociatedObject(id?object,?const?void?*key,?id?value,?objc_AssociationPolicy?policy)
__OSX_AVAILABLE_STARTING(__MAC_10_6,?__IPHONE_3_1);
OBJC_EXPORT?id?objc_getAssociatedObject(id?object,?const?void?*key)
__OSX_AVAILABLE_STARTING(__MAC_10_6,?__IPHONE_3_1);

另外還有一個方法：

OBJC_EXPORT?void?objc_removeAssociatedObjects(id?object)
__OSX_AVAILABLE_STARTING(__MAC_10_6,?__IPHONE_3_1);

objc_getAssociatedObject、objc_setAssociatedObject、objc_removeAssociatedObjects都是Obj-c中的外聯方法，object 參數作為待擴展的對象實例，key作為該對象實例的屬性的鍵，而value就是對象實例的屬性的值，policy作為關聯的策略，它的枚舉包括：

enum?{
OBJC_ASSOCIATION_ASSIGN?=?0,
OBJC_ASSOCIATION_RETAIN_NONATOMIC?=?1,
OBJC_ASSOCIATION_COPY_NONATOMIC?=?3,
OBJC_ASSOCIATION_RETAIN?=?01401,
OBJC_ASSOCIATION_COPY?=?01403
};

具體我就多說了，可以看得懂的。

另外，objc_removeAssociatedObjects可以刪除指定對象實例的所有擴展屬性。

現在看一個簡單的例子：（引用網上的例子:http://code4app.com/ios/Block-UI/504fe65d6803faa33f000003?）

這里，定義了一個"alert view"的按鈕：

UIButton?*button?=?[UIButton?buttonWithType:UIButtonTypeRoundedRect];
[viewController.view?addSubview:button];
button.frame?=?CGRectMake(50,?50,?100,?44);
[button?setTitle:@"alert?view"?forState:UIControlStateNormal];

現在對UIButton通過使用category對其進行方法擴展：

@implementation?UIControl?(BUIControl)
…...
-?(void)handleControlEvent:(UIControlEvents)event?withBlock:(void(^)(id?sender))block?{
NSString?*methodName?=?[UIControl?eventName:event];
NSMutableDictionary?*opreations?=?(NSMutableDictionary*)objc_getAssociatedObject(self,?&OperationKey);
if(opreations?==?nil)
{
opreations?=?[[NSMutableDictionary?alloc]?init];
objc_setAssociatedObject(self,?&OperationKey,?opreations,?OBJC_ASSOCIATION_RETAIN);
}
[opreations?setObject:block?forKey:methodName];
[self?addTarget:self?action:NSSelectorFromString(methodName)?forControlEvents:event];
}

objc_getAssociatedObject，objc_setAssociatedObject進行屬性擴展：

OperationKey是一個字符類型，這里表示一個鍵，如果Opreations為空，會setAssociatedObject一個新的opreations對象到對應鍵的值中間。

addTarget:action:forControlEvents對于觸摸事件進行目標綁定。

NSSelectorFromString(methodName) 將觸發方法：

-(void)UIControlEventTouchDown{[self?callActionBlock:UIControlEventTouchDown];}
-(void)UIControlEventTouchDownRepeat{[self?callActionBlock:UIControlEventTouchDownRepeat];}
-(void)UIControlEventTouchDragInside{[self?callActionBlock:UIControlEventTouchDragInside];}
-(void)UIControlEventTouchDragOutside{[self?callActionBlock:UIControlEventTouchDragOutside];}
-(void)UIControlEventTouchDragEnter{[self?callActionBlock:UIControlEventTouchDragEnter];}
-(void)UIControlEventTouchDragExit{[self?callActionBlock:UIControlEventTouchDragExit];}
-(void)UIControlEventTouchUpInside{[self?callActionBlock:UIControlEventTouchUpInside];}
-(void)UIControlEventTouchUpOutside{[self?callActionBlock:UIControlEventTouchUpOutside];}
-(void)UIControlEventTouchCancel{[self?callActionBlock:UIControlEventTouchCancel];}
-(void)UIControlEventValueChanged{[self?callActionBlock:UIControlEventValueChanged];}
-(void)UIControlEventEditingDidBegin{[self?callActionBlock:UIControlEventEditingDidBegin];}
-(void)UIControlEventEditingChanged{[self?callActionBlock:UIControlEventEditingChanged];}
-(void)UIControlEventEditingDidEnd{[self?callActionBlock:UIControlEventEditingDidEnd];}
-(void)UIControlEventEditingDidEndOnExit{[self?callActionBlock:UIControlEventEditingDidEndOnExit];}
-(void)UIControlEventAllTouchEvents{[self?callActionBlock:UIControlEventAllTouchEvents];}
-(void)UIControlEventAllEditingEvents{[self?callActionBlock:UIControlEventAllEditingEvents];}
-(void)UIControlEventApplicationReserved{[self?callActionBlock:UIControlEventApplicationReserved];}
-(void)UIControlEventSystemReserved{[self?callActionBlock:UIControlEventSystemReserved];}
-(void)UIControlEventAllEvents{[self?callActionBlock:UIControlEventAllEvents];}

注意到這里會去執行callActionBlock:方法：

-?(void)callActionBlock:(UIControlEvents)event?{
NSMutableDictionary?*opreations?=?(NSMutableDictionary*)objc_getAssociatedObject(self,?&OperationKey);
if(opreations?==?nil)?return;
void(^block)(id?sender)?=?[opreations?objectForKey:[UIControl?eventName:event]];
if?(block)?block(self);
}

最終會從擴展屬性中得到^block，關于^block可以參考：http://blog.csdn.net/pjk1129/article/details/6577097

最后調用：

[button?handleControlEvent:UIControlEventTouchUpInside?withBlock:^(id?sender)?{
UIAlertView?*alert?=?[[UIAlertView?alloc]?initWithTitle:@"alert"
message:nil
delegate:nil
cancelButtonTitle:@"ok"
otherButtonTitles:@"other",nil];
}];

點擊按鈕就會觸發一個block函數。

這樣就實現了objective-c的兩種擴展機制。

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作者：Leepy 郵箱：sunleepy(AT)gmail.com 出處：http://liping13599168.cnblogs.com/? 　　　　 本文版權歸作者和博客園共有，歡迎轉載，但未經作者同意必須保留此段聲明，且在文章頁面明顯位置給出原文鏈接，否則保留追究法律責任的權利。

轉載于:https://www.cnblogs.com/zsw-1993/p/4879856.html

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