Association-simple and violent setting properties for objects

In short, an association function forcibly sets attributes for an object and is generally used to impose attributes on the system class.

1. pass two instance objects through the button

Uibutton * BTN = // create button, omitted .. objc_setassociatedobject (BTN, "firstobject", someobject, callback); values (BTN, "secondobject", otherobject, callback); [BTN addtarget: Self action: @ selector (Click :) forcontrolevents: uicontroleventtouchupinside];-(void) Click :( uibutton *) sender {ID first = objc_getassociatedobject (sender, "firstobject ");
Id second = objc_setassociatedobject (sender, "secondobject"); // etc.
}

Like the above method, when the button is passed to the selector, two attributes are forcibly added to the button.

Step: 1) set Association

　　　　objc_setAssociatedObject(btn, "firstObject", someObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

　　　　BTN: connected by firstobject: pointer to the correlated object (Generally, it is a static string). The third parameter is the associated object instance, and the fourth parameter is the association method (there are several parameters, such as assign and retain when setting the. h file attribute)

2) Get the associated object

ID first = objc_getassociatedobject (sender, "firstobject ");

Parameter 1: Joined parameter 2: pointer

2. Block can also be passed.

We often write button click events. We can use Association/block callback/category to add a method to the button to implement block direct callback without writing click events.

Uicontrol + blocks. h

#import <UIKit/UIKit.h>#import <objc/runtime.h>typedef void (^ActionBlock)(id sender);@interface UIControl (Blocks)- (void)addEventHandler:(ActionBlock)handler forControlEvents:(UIControlEvents)controlEvents;@end

Uicontrol + blocks. m

#import "UIControl+Blocks.h"static char UIButtonHandlerKey;@implementation UIControl (Blocks)- (void)addEventHandler:(ActionBlock)handler forControlEvents:(UIControlEvents)controlEvents{    objc_setAssociatedObject(self, &UIButtonHandlerKey, handler, OBJC_ASSOCIATION_COPY_NONATOMIC);    [self addTarget:self action:@selector(callActionHandler:) forControlEvents:controlEvents];}- (void)callActionHandler:(id)sender{    ActionBlock handler = (ActionBlock)objc_getAssociatedObject(self, &UIButtonHandlerKey);    if (handler) {        handler(sender);    }}@end

 

Association-simple and violent setting properties for objects