Objective_C extension mechanism Learning

Objective_CExtensionMechanismLearning is the content to be introduced in this article.Objective_CIt has been one year since the iphone was developed. FirstObjective_CWhen c/c ++ is used, the knowledge learned is based on c/c ++. In factObjective_CThe superset of C was not realized at that time, and its essence was not understood at all. Learn more with the passage of time.

Objective_CIt is more powerful than c/c ++ because it contains some design patterns. I have heard that java includes almost all the design patterns, but I have never used java in depth, and I have used j2s to write a little logic. The two most flexible aspects of Objective_C are: category and associative. I classify them as extensions of Objective_C.Mechanism. Category can extend a class method, and associative can extend the attributes of a class. The functions of these two methods are equivalent to the inheritance in c ++.

Let's take a look at the associative column. The header file is required:

 
 

  
  
#import <objc/runtime.h> 
  
  
 
  
  
static char overviewKey = 'a';    
  
  
NSArray *array = [[NSArray alloc] initWithObjects:@ "One", @"Two", @"Three", nil];    
  
  
// For the purposes of illustration, use initWithFormat: to ensure      
  
  
// we get a deallocatable string      
  
  
NSString *overview = [[NSString alloc] initWithFormat:@"%@", @"First three numbers"];    
  
  
objc_setAssociatedObject ( array, &overviewKey, overview, OBJC_ASSOCIATION_RETAIN);     
  
  
[overview release];    
  
  
NSString *associatedObject = (NSString *) objc_getAssociatedObject (array, &overviewKey);    
  
  
NSLog(@"associatedObject: %@", associatedObject);    
  
  
objc_setAssociatedObject ( array, &overviewKey, nil, OBJC_ASSOCIATION_ASSIGN );     
  
  
[array release];    
  
  
 static char overviewKey = 'a';  
  
  
 NSArray *array = [[NSArray alloc] initWithObjects:@ "One", @"Two", @"Three", nil];  
  
  
 // For the purposes of illustration, use initWithFormat: to ensure   
  
  
 // we get a deallocatable string   
  
  
 NSString *overview = [[NSString alloc] initWithFormat:@"%@", @"First three numbers"];  
  
  
 objc_setAssociatedObject ( array, &overviewKey, overview, OBJC_ASSOCIATION_RETAIN);   
  
  
 [overview release];  
  
  
 NSString *associatedObject = (NSString *) objc_getAssociatedObject (array, &overviewKey);  
  
  
 NSLog(@"associatedObject: %@", associatedObject);  
  
  
 objc_setAssociatedObject ( array, &overviewKey, nil, OBJC_ASSOCIATION_ASSIGN );   
  
  
 [array release]; 
 
 

Objc_setAssociatedObject adds an attribute to the array. We can obtain this attribute through the key. See the code above: objc_getAssociatedObject. If the second objc_setAssociatedObject is set to nil, this attribute is deleted.

Here is another example: callback.

Summary: DetailsObjective_CExtensionMechanismI hope this article will be helpful to you!