OBJECTIVE-C Foundation: Fourth day-7. Class loading process

In the front, we know that the nature of the class is actually an object, is the class type, then the loading process is how? In fact, the loading process of the class is very simple, first load the parent class and then load the subclass, and each class will only be loaded once, let's look at the following ~

Example:

#import <Foundation/Foundation.h>

@interface person:nsobject
+ (void) load;
@end

@implementation person
+ (void) load
{
    NSLog (@ ' person-----load ');
}
@end

@interface Student:person
+ (void) load;
@end

@implementation Student
+ (void) load
{
    NSLog (@ "Student-----load");
}
@end

int main ()
{
    return 0;
}

In the main () function, there is no call to the class method set, load this class method is automatically called by the system, so we do not need to call ourselves.

Results:

2015-01-24 14:14:45.451 07-Nature of the class [10689:1160313] person----load
2015-01-24 14:14:45.452 07-The nature of the class [10,689:1,160,313] Student----Load

From the result, we can see that the system first loads the person and then loads the student.

And if we need to listen, when does it load? There is also a method called + (void) Initialize, let's take a look at:

#import <Foundation/Foundation.h>

@interface person:nsobject
+ (void) load;
@end

@implementation person
+ (void) load
{
    NSLog (@ ' person-----load ');
}
+ (void) Initialize
{
    NSLog (@ "person-initialize");
}
@end

@interface Student:person
+ (void) load;
@end

@implementation Student
+ (void) load
{
    NSLog (@ "Student-----load");
}
+ (void) Initialize
{
    NSLog (@ "student-initialize");
}
@end

int main ()
{
    [[Student alloc]init];
    return 0;
}

Results:

2015-01-24 14:24:18.588 07-Nature of the class [10729:1164951] person----load
2015-01-24 14:24:18.589 07-The nature of the class [10,729:1,164,951] Student----Load
2015-01-24 14:24:18.589 07-Nature of the class [10729:1164951] person-initialize
2015-01-24 14:24:18.590 07 -The nature of the class [10729:1164951] Student-initialize

If we change the main () function:

int main ()
{
	[[person alloc]init];
	return 0;
}

So the result is:

2015-01-24 14:25:17.760 07-Nature of the class [10738:1165590] person----load
2015-01-24 14:25:17.761 07-The nature of the class [10,738:1,165,590] Student----Load
2015-01-24 14:25:17.761 07-Nature of the class [10738:1165590] Person-initialize

The reason is very simple, in the main () function, if we have loaded into the subclass, then the Initialize method is from the parent class has been loaded into the child class, but if only the parent class, then the subclass will not be loaded.

The Load method is detailed: When the program starts, it loads all the classes in the project, and the class loads and then calls the + (void) Load method.
Initialize method: When using this class for the first time, the + (void) Initialize method is loaded.

OK, this time we'll talk about this, next time we continue to ~ ~