Objective-c class method Self keyword

NSString basic use

#import <Foundation / Foundation.h>

int main () {
    // The easiest way to create a string
    NSString * str = @ "大 武汉";
    NSLog (@ "我 在% @", str);
    
    // Another way to create a string
    int age = 15;
    int no = 5668;
    NSString * name = @ "黄 祎 a";
    NSString * newStr = [NSString stringWithFormat: @ "My age is% i and My no is% i and My name is% @", age, no, name];
    NSLog (@ "---------% @", newStr);
    
    // Get the length of the string
    int size = [name length];
    NSLog (@ "name length is% i", size);
    return 0;
}
Class method

#import <Foundation / Foundation.h>

@interface Person: NSObject
+ (void) test;
@end

@implementation Person
+ (void) test {
    NSLog (@ "hello world");
}
@end

int main () {
    [Person test];
    return 0;
}

/ *
 Object method
    Starts with-<only> callable by object
    Object methods can use member variables
    Relatively inefficient
 
 Class method
    Starts with + <only> can be called by class
    Class methods cannot use member variables
    Relatively efficient
 
 Object method name allowed in a class = class method name
 * /
self keyword

#import <Foundation / Foundation.h>

@interface Person: NSObject {
    @public
    int _age;
}
-(void) show;
-(void) test1;
-(void) test2;
@end

@implementation Person
-(void) show {
    NSLog (@ "Person's age is% i", _age);
}
-(void) test1 {
    int _age = 20;
    NSLog (@ "Person's age is% i", _age);
}
-(void) test2 {
    int _age = 30;
    NSLog (@ "Person's age is% i", self-> _ age);
}
@end

int main () {
    Person * p = [Person new];
    [p show];
    [p test1];
    [p test2];
    return 0;
}

// When the member variable and the local variable have the same name, the principle of proximity is used.
// Use self to access member variables Distinguish member variables from local variables

/ ** Application details ** /
// where it appears: all OC methods (object methods | class methods) cannot appear in functions
// Function: Use ‘self-> member variable name’ to access the member variables of the current method call; use ‘[self method name]’ to call the method (object method | class method)

/ ** Common errors ** /
// Use self to call the function
// Use self to call object method in class method Use self to call class method in object method
// self infinite loop
Objective-C class method self keyword