iOS develops a simple summary of SEL

SEL is a wrapper for the method. Package SEL type data it corresponds to the corresponding method address and can be called by locating the method address. The methods of each class in memory are stored in the class object, each method has a corresponding SEL type of data, according to a SEL data can find the corresponding method address, and then call the method.

1. @interface Person:nsobject
3. + (void) test1;
4. -(void) test2;
5. @end
7. //According to the person class and method defined in the. h file, this line of code is executed in memory as follows
8. Person *person = [[Person alloc] init];

SEL is a wrapper for the method. Package SEL type data it corresponds to the corresponding method address, find the method address to call the method

1. Where to store the method

• The methods of each class in memory are stored in the class object
• Each method has a corresponding SEL type of data
• The corresponding method address can be found based on a SEL data, which in turn calls the method
• Definition of SEL type: typedef struct OBJC_SELECTOR *sel

Creation of 2.SEL objects

1. SEL S1 = @selector (test1); //Wrap the Test1 method into a Sel object
2. SEL s2 = nsselectorfromstring (@"test1"); //Convert a string method to a Sel object

Other uses of 3.SEL objects

1. Convert a Sel object to a NSString object
2. NSString *str = Nsstringfromselector (@selector (test));
4. Person *p = [person new];
6. Call the test method of the object P
7. [P Performselector: @selector (test)];

2. /******************************* Person.h File **********************************/
6. #import <Foundation/Foundation.h>
10. @interface Person:nsobject
14. -(void) test1;
18. -(void) Test2: (NSString *) str;
22. @end
26. /******************************* person.m File **********************************/
30. #import "Person.h"
34. @implementation person
38. -(void) test1
40. {
42. NSLog (@"non-Parametric object method");
44. }
48. -(void) Test2: (NSString *) str
50. {
52. NSLog (@"method%@ with Parameters", str);
54. }
56. @end
60. /******************************* main.m File **********************************/
64. #import "Person.h"
66. #import <Foundation/Foundation.h>
70. /*
72. There are two ways to invoke a method:
74. 1. Calling directly from the method name
76. 2. Indirectly through the SEL data to invoke
78. */
82. int main (int argc, const char * argv[])
84. {
86. Person *person = [[Person alloc] init];
90. //1. When executing this line of code, the Test2 is packaged into SEL type data
92. //2. Then find the corresponding method address according to the SEL data (compare consumption performance but the system will have cache)
94. //3. Call the corresponding method according to the method address
98. [Person test1];
102. //The method is packaged directly into the SEL data type to invoke Withobject: Incoming parameters
104. [Person Performselector: @selector (test1)];
106. [Person Performselector: @selector (test2:) withobject:@"incoming parameters"];
110. return 0;
112. }

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iOS develops a simple summary of SEL