Object initialization

List of articles

Chapter one OC The singleton model
Chapter two OC Initialization of
The third chapter OC And agreements
Chapter four OC And main Some operations and basic concepts of functions

Preface

Talking about initialization method and rewriting of initialization method

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One 、 Object initialization ？

• What is object initialization ？

After we create an object , Assigning values to its properties is called object initialization

• Allocate space for objects ：

[[ Class name alloc]init]
[ Class name new]
These two methods are essentially the same .

• Reset the memory space of each instance variable to 0;

The shaping variable is reset to 0, Floating point objects are reset to 0.0.BOOL Type reset to NO.

• The function of initialization

Objects that only allocate memory cannot be used , Must be initialized ,OC The most common initialization method is init.
init Method can complete initialization , But it just completes the most basic initialization , therefore , All member variables of the object are still 0

Let's see if Not initialized What will happen ：

Class interface ：

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface User : NSObject
@property(nonatomic,copy) NSString*name;
@property(nonatomic,assign) int age;

@end

NS_ASSUME_NONNULL_END

The realization of the class ：

 Insert a code chip here #import "User.h"

@implementation User
@synthesize name;
@synthesize age;
@end;

test ：

#import"User.h"
#import<Foundation/Foundation.h>
int main() {
    
    @autoreleasepool {
    
        User* user = [[User alloc]init];
        NSLog(@"user.name = %@,user.age = %d", user.name, user.age);
        
    }
}

result ：

Here we see the importance of initialization .

Two 、 Initialization method

The interface and implementation of the class are the same as above , Give the test part ：

#import"User.h"
#import<Foundation/Foundation.h>
int main(){
    
    @autoreleasepool {
    
        User* user = [[User alloc]init];
        user.name = @" Nana ";
        user.age = 18;
        NSLog(@"user.name = %@,user.age = %d", user.name, user.age);
        
    }
}

result ：

3、 ... and 、 Override initialization method

Class interface ：

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface User : NSObject
@property(nonatomic,copy) NSString*name;
@property(nonatomic,assign) int age;

@end

NS_ASSUME_NONNULL_END

The realization of the class ：

#import "User.h"

@implementation User
@synthesize name;
@synthesize age;
-(id)init{
    
    if(self = [super init]){
    
        self.name = @"wang";
        self.age = 18;
    }
    return self;
}
@end

Test part ：

#import"User.h"
#import<Foundation/Foundation.h>
int main(){
    
    @autoreleasepool {
    
        User* user = [[User alloc]init];
        NSLog(@"user.name = %@,user.age = %d", user.name, user.age);
        User* m = [[User alloc]init];
        NSLog(@"m.name = %@,m.age = %d", user.name, user.age);
    }
}

result ：

We found that , These two objects are calling init When the method is used , Will automatically assign values to objects . Because we rewrite init Method , What we use here is init The method is no longer NSObject Provided , But we rewrite . Before we call the rewritten init After the method , Will automatically assign values to objects .