Summary of SEL in iOS development

 
 

  
  
@ Interface Person: NSObject
  
  
 
  
  
+ (Void) test1;
  
  
-(Void) test2;
  
  
@ End
  
  
 
  
  
// Execute this line of code based on the Person class and method defined in the. h file as follows in the memory
  
  
Person * person = [[Person alloc] init];
 
 

SEL is a method packaging. The encapsulated SEL data corresponds to the corresponding method address. You can call the method by finding the method address.

1. storage location of the Method

• In memory, methods of each class are stored in class objects.
• Each method has a SEL-type data corresponding to it.
• You can find the corresponding method address based on a SEL data and call the method.
• SEL Type Definition: typedef struct objc_selector * SEL

2. Create a SEL object

 
 

  
  
SEL s1 = @ selector (test1); // wrap the test1 method into a SEL object
  
  
SEL s2 = NSSelectorFromString (@ "test1"); // convert a string method to a SEL object
 
 

3. Other SEL object usage

 
 

  
  
// Convert SEL object to NSString object
  
  
NSString * str = NSStringFromSelector (@ selector (test ));
  
  
 
  
  
Person * p = [Person new];
  
  
 
  
  
// Call the test method of object p
  
  
[P performSelector: @ selector (test)];

 
 

 
 

  
  
/******************************* Person. h file **********************************/
  
  
 
  
  
# Import <Foundation/Foundation. h>
  
  
 
  
  
@ Interface Person: NSObject
  
  
 
  
  
-(Void) test1;
  
  
 
  
  
-(Void) test2 :( NSString *) str;
  
  
 
  
  
@ End
  
  
 
  
  
/******************************* Person. m file **********************************/
  
  
 
  
  
# Import "Person. h"
  
  
 
  
  
@ Implementation Person
  
  
 
  
  
-(Void) test1
  
  
{
  
  
NSLog (@ "Object method without Parameters ");
  
  
}
  
  
 
  
  
-(Void) test2 :( NSString *) str
  
  
{
  
  
NSLog (@ "method with parameters % @", str );
  
  
}
  
  
@ End
  
  
 
  
  
/******************************* Main. m file **********************************/
  
  
 
  
  
# Import "Person. h"
  
  
# Import <Foundation/Foundation. h>
  
  
 
  
  
/*
  
  
There are two ways to call a method:
  
  
1. Call the method name directly.
  
  
2. Indirectly calling through SEL data
  
  
*/
  
  
 
  
  
Int main (int argc, const char * argv [])
  
  
{
  
  
Person * person = [[Person alloc] init];
  
  

  
  
// 1. When this line of code is executed, test2 will be packaged into SEL-type data
  
  
// 2. Find the corresponding method address based on the SEL data (performance consumption is compared, but the system will cache)
  
  
// 3. Call the corresponding method based on the method address
  
  

  
  
[Person test1];
  
  

  
  
// Wrap the method directly into the SEL data type to call withObject: input parameter
  
  
[Person primary mselector: @ selector (test1)];
  
  
[Person required mselector: @ selector (test2 :) withObject: @ "Incoming parameter"];
  
  

  
  
Return 0;
  
  
}