IOS extension mechanism category and associative

When writing Sina Weibo, I want to solve the problem of clicking Weibo image enlargement. Here I am using the category and associative extension mechanisms to add a method and an attribute to the uiimageview extension, this method is used to enlarge the clicked image, and this attribute is the URL of the download link of the image.

The two extension mechanisms are described below:

Category and associative are two features of the objective-C extension mechanism. category can be used to expand the method; associative can use it to expand attributes.

During iOS development, the former category is more common and simple. Here we will not talk about it. Here we will mainly talk about associative;

The latter associative is less commonly used. To use associative, you must use # Import
<Objc/runtime. h>, and then call the objc_setassociatedobject and objc_getassociatedobject methods to add the setter and getter methods to the attributes respectively to implement attribute extension.

The following two methods are described:

①: Void objc_setassociatedobject (ID object, void * Key, id value, objc_associationpolicy Policy)

The parameters are as follows:

Parameters

Object: the source object for the association.

Key: the key for the association.

Value: the value to associate with the key for object. Pass nil to clear an existing association.

Policy: the Policy for the Association

The policy includes

Enum {

Objc_association_assign = 0,

Objc_association_retain_nonatomic = 1,

Objc_association_copy_nonatomic = 3,

Objc_association_retain = 01401,

Objc_association_copy = 01403

};

②: Id objc_getassociatedobject (ID object, void * key)

Parameters

Object: the source object for the association.

Key: the key for the association.

Return Value

The value associated with the key for object.

All of them are relatively simple. Here is a demo to describe them!

Here I want to extend uiimageview to add a method and an attribute for it.

The header file of category:

#import <UIKit/UIKit.h>@interface UIImageView (associate)@property(nonatomic,strong)NSString* myString;-(void)Output;@end

CATEGORY implementation file:

#import <objc/runtime.h>#import "UIImageView+associate.h"static void * MyKey = (void *)@"MyKey";@implementation UIImageView (associate)-(NSString*)myString {    return objc_getAssociatedObject(self, MyKey);}-(void)setMyString:(NSString *)string {    objc_setAssociatedObject(self, MyKey, string, OBJC_ASSOCIATION_COPY_NONATOMIC);}-(void)Output {    NSLog(@"output mystring:%@",self.myString);}@end

Note: An Attribute and a method are added to the header file, and the setter and getter methods are rewritten for the attribute using the associative feature in the implementation file, which is relatively simple.

Test:

UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Icon@2x.png"]];    imageView.bounds = CGRectMake(50, 50, 100, 100);    imageView.myString = @"hello world";    [self.view addSubview:imageView];        [imageView Output];

After running, an image is displayed on the simulator. The terminal output is output mystring: Hello world.