load方法和initialize方法異同

load方法和initialize方法異同

  • load方法會(huì)在加載類的時(shí)候就被調(diào)用，也就是說iOS應(yīng)用啟動(dòng)的時(shí)候，就會(huì)加載所有的類，會(huì)調(diào)用每個(gè)類的+load方法。

+load方法舉例

-新建父類Person類 并在.m里面實(shí)現(xiàn)+load方法

#import <Foundation/Foundation.h>
@interface Person : NSObject
@end

#import "Person.h"

@implementation Person
+(void)load
{
    NSLog(@"%s",__func__);
}
@end

繼承Person類新建子類Son類 并在.m里面實(shí)現(xiàn)+load方法

#import "Person.h"
@interface Son : Person
@end

#import "Son.h"

@implementation Son
+(void)load
{
    NSLog(@"%s",__func__);
}
@end

給父類Person類創(chuàng)建Category 并且在.m里面實(shí)現(xiàn)+load方法

#import "Person.h"

@interface Person (Category)
@end

#import "Person+Category.h"

#import <AppKit/AppKit.h>


@implementation Person (Category)
+(void)load
{
    NSLog(@"%s",__func__);
}
@end

運(yùn)行打印

2019-10-23 11:41:35.366135+0800 load+initialize[1673:96489] +[Person load]
2019-10-23 11:41:35.366666+0800 load+initialize[1673:96489] +[Son load]
2019-10-23 11:41:35.366721+0800 load+initialize[1673:96489] +[Person(Category) load]
2019-10-23 11:41:35.366845+0800 load+initialize[1673:96489] main, Hello World!
Program ended with exit code: 0
  • 實(shí)操證明+load方法在對(duì)類沒有進(jìn)行任何操作的情況下默認(rèn)調(diào)用而且在main函數(shù)之前調(diào)用。
  • 調(diào)用順序：父類---> 子類---> 分類
  • 平級(jí)調(diào)用順序 （例如又創(chuàng)建了person2類 ）這個(gè)時(shí)候的調(diào)用順序?yàn)轫?xiàng)目-->TARGETS —>Build Phases -->Compile Sources -加載的順序

+initialize方法舉例

在上述Person類.m中實(shí)現(xiàn)+(void)initialize方法

#import "Person.h"

@implementation Person
+(void)load
{
    NSLog(@"%s",__func__);
}


+(void)initialize
{
    NSLog(@"%s",__func__);
}

- (instancetype)init
{
    self = [super init];
      if (self) {
             NSLog(@"%s",__func__);
      }
      return self;
}

@end
  • 運(yùn)行發(fā)現(xiàn)沒有initialize方法調(diào)用

在main函數(shù)中初始化

#import <Foundation/Foundation.h>
#import "Person.h"
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        NSLog(@"%s, Hello World!",__func__);
        
       Person * person = [[Person alloc]init];
 
        
        
    }
    return 0;
}


------------------------load-----------------------------------------
2019-10-23 12:57:52.431490+0800 load+initialize[2080:126579] +[Person load]
2019-10-23 12:57:52.432133+0800 load+initialize[2080:126579] +[Son load]
2019-10-23 12:57:52.432369+0800 load+initialize[2080:126579] +[Person(Category) load]
2019-10-23 12:57:52.432614+0800 load+initialize[2080:126579] main, Hello World!
------------------------initialize----------------------------------------
2019-10-23 12:57:52.432687+0800 load+initialize[2080:126579] +[Person initialize]
2019-10-23 12:57:52.432841+0800 load+initialize[2080:126579] -[Person init]
Program ended with exit code: 0
  • 運(yùn)行發(fā)現(xiàn)initialize方法在init方法前調(diào)用

這時(shí)在Person+Category.m中實(shí)現(xiàn)initialize方法 并且運(yùn)行

#import "Person+Category.h"

#import <AppKit/AppKit.h>


@implementation Person (Category)
+(void)load
{
    NSLog(@"%s",__func__);
}


+(void)initialize
{
    NSLog(@"%s",__func__);
}
@end

------------------------load-----------------------------------------
2019-10-23 13:02:33.317059+0800 load+initialize[2128:128769] +[Person load]
2019-10-23 13:02:33.318109+0800 load+initialize[2128:128769] +[Son load]
2019-10-23 13:02:33.318562+0800 load+initialize[2128:128769] +[Person(Category) load]
2019-10-23 13:02:33.318907+0800 load+initialize[2128:128769] main, Hello World!
------------------------initialize----------------------------------------
2019-10-23 13:02:33.319210+0800 load+initialize[2128:128769] +[Person(Category) initialize]
2019-10-23 13:02:33.319515+0800 load+initialize[2128:128769] -[Person init]
Program ended with exit code: 0
  • 運(yùn)行發(fā)現(xiàn)Person的方法被Person+Category里的initialize方法替換

這時(shí)在Son類中實(shí)現(xiàn)+initialize方法 并且在main函數(shù)中初始化并運(yùn)行

#import "Son.h"

@implementation Son
+(void)load
{
    NSLog(@"%s",__func__);
}



+(void)initialize
{
    NSLog(@"%s",__func__);
}
- (instancetype)init
{
    self = [super init];
    if (self) {
         NSLog(@"%s",__func__);
    }
    return self;
}

@end

#import <Foundation/Foundation.h>
#import "Person.h"
#import "Son.h"
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        NSLog(@"%s, Hello World!",__func__);
       
            Person * person = [[Person alloc]init];
            
            Son * son = [[Son alloc]init];
        
        
    }
    return 0;
}


------------------------load-----------------------------------------
2019-10-23 13:16:06.456182+0800 load+initialize[2362:141389] +[Person load]
2019-10-23 13:16:06.456668+0800 load+initialize[2362:141389] +[Son load]
2019-10-23 13:16:06.456877+0800 load+initialize[2362:141389] +[Person(Category) load]
2019-10-23 13:16:06.457197+0800 load+initialize[2362:141389] main, Hello World!
------------------------initialize----------------------------------------
2019-10-23 13:16:06.457270+0800 load+initialize[2362:141389] +[Person(Category) initialize]
2019-10-23 13:16:06.457411+0800 load+initialize[2362:141389] -[Person init]
2019-10-23 13:16:06.457516+0800 load+initialize[2362:141389] +[Son initialize]
2019-10-23 13:16:06.457632+0800 load+initialize[2362:141389] -[Person init]
2019-10-23 13:16:06.457724+0800 load+initialize[2362:141389] -[Son init]
Program ended with exit code: 0
  • 運(yùn)行發(fā)現(xiàn)Person的方法被Person+Category里的initialize方法替換 無論初始化多少次 Person+Category.m里的方法只會(huì)調(diào)用一次（猜測(cè)如果沒有分類那么父類的initialize也只會(huì)調(diào)用一次下面論證)

這時(shí)將main函數(shù)里的父類初始化去掉運(yùn)行

#import <Foundation/Foundation.h>
#import "Person.h"
#import "Son.h"
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        NSLog(@"%s, Hello World!",__func__);
       
            ///////Person * person = [[Person alloc]init];
            Son * son = [[Son alloc]init];
        
        
    }
    return 0;
}


------------------------load-----------------------------------------
2019-10-23 13:22:37.053879+0800 load+initialize[2414:144467] +[Person load]
2019-10-23 13:22:37.054447+0800 load+initialize[2414:144467] +[Son load]
2019-10-23 13:22:37.054611+0800 load+initialize[2414:144467] +[Person(Category) load]
2019-10-23 13:22:37.054742+0800 load+initialize[2414:144467] main, Hello World!
------------------------initialize----------------------------------------
2019-10-23 13:22:37.054797+0800 load+initialize[2414:144467] +[Person(Category) initialize]
2019-10-23 13:22:37.054842+0800 load+initialize[2414:144467] +[Son initialize]
2019-10-23 13:22:37.054889+0800 load+initialize[2414:144467] -[Person init]
2019-10-23 13:22:37.054929+0800 load+initialize[2414:144467] -[Son init]
Program ended with exit code: 0
  • 運(yùn)行發(fā)現(xiàn)初始化子類 父類的分類里的initialize會(huì)被調(diào)用（猜測(cè)如果沒有分類那么會(huì)先調(diào)用父類的initialize ）在調(diào)用子類的initialize

好的乘勝追擊 這時(shí)將分類里的initialize方法去掉 再次運(yùn)行

#import "Person+Category.h"

#import <AppKit/AppKit.h>


@implementation Person (Category)
+(void)load
{
    NSLog(@"%s",__func__);
}

//
//+(void)initialize
//{
//    NSLog(@"%s",__func__);
//}
@end


------------------------load----------------------------------------
2019-10-23 13:28:14.368976+0800 load+initialize[2484:146913] +[Person load]
2019-10-23 13:28:14.369644+0800 load+initialize[2484:146913] +[Son load]
2019-10-23 13:28:14.369725+0800 load+initialize[2484:146913] +[Person(Category) load]
2019-10-23 13:28:14.369850+0800 load+initialize[2484:146913] main, Hello World!

------------------------initialize----------------------------------------
2019-10-23 13:28:14.369904+0800 load+initialize[2484:146913] +[Person initialize]
2019-10-23 13:28:14.369946+0800 load+initialize[2484:146913] +[Son initialize]
2019-10-23 13:28:14.369993+0800 load+initialize[2484:146913] -[Person init]
2019-10-23 13:28:14.370032+0800 load+initialize[2484:146913] -[Son init]
  • 發(fā)現(xiàn)只初始化子類父類的initialize會(huì)調(diào)用 父類有分類并實(shí)現(xiàn)initialize方法會(huì)會(huì)把 父類里分方法替換掉 父類不會(huì)在調(diào)用 （分類里實(shí)現(xiàn)initialize方法會(huì)把類里面的initialize方法替換掉）

這時(shí)候打開main函數(shù)的父類初始化 子類與父類進(jìn)行多次初始化 并運(yùn)行

#import <Foundation/Foundation.h>
#import "Person.h"
#import "Son.h"
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        NSLog(@"%s, Hello World!",__func__);
       
         Person * person = [[Person alloc]init];
            Person * person1 = [[Person alloc]init];
            Person * person2 = [[Person alloc]init];
            Person * person3 = [[Person alloc]init];
   
        Son * son = [[Son alloc]init];
               Son * son1 = [[Son alloc]init];
               Son * son2 = [[Son alloc]init];
               Son * son3 = [[Son alloc]init];
    
        
    }
    return 0;
}

------------------------load-----------------------------------------
2019-10-23 13:46:03.090877+0800 load+initialize[2697:156107] +[Person load]
2019-10-23 13:46:03.091536+0800 load+initialize[2697:156107] +[Son load]
2019-10-23 13:46:03.091603+0800 load+initialize[2697:156107] +[Person(Category) load]
2019-10-23 13:46:03.091728+0800 load+initialize[2697:156107] main, Hello World!
------------------------initialize----------------------------------------
2019-10-23 13:46:03.091937+0800 load+initialize[2697:156107] +[Person initialize]
2019-10-23 13:46:03.092105+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.092155+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.092196+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.092236+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.092276+0800 load+initialize[2697:156107] +[Son initialize]
2019-10-23 13:46:03.092318+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.092371+0800 load+initialize[2697:156107] -[Son init]
2019-10-23 13:46:03.092411+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.092448+0800 load+initialize[2697:156107] -[Son init]
2019-10-23 13:46:03.092487+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.094391+0800 load+initialize[2697:156107] -[Son init]
2019-10-23 13:46:03.094461+0800 load+initialize[2697:156107] -[Person init]
2019-10-23 13:46:03.094511+0800 load+initialize[2697:156107] -[Son init]
  • 發(fā)現(xiàn)無論你初始化多少次 initialize方法 有且只會(huì)調(diào)用一次

總結(jié)

load

  • load的方法編譯器自動(dòng)調(diào)用 每個(gè)類都會(huì)調(diào)用 并且在main函數(shù)之前調(diào)用
  • 每個(gè)類的調(diào)用順序跟項(xiàng)目加載的順序有關(guān)具體請(qǐng)看項(xiàng)目-->TARGETS —>Build Phases -->Compile Sources -加載的順序（從上往下調(diào)用）
  • 繼承關(guān)系并且父類實(shí)現(xiàn)分類 順序?yàn)?父類 ->子類->分類

initialize

  • 類初始化的時(shí)候調(diào)用 無論類初始化多少次 只會(huì)調(diào)用一次（在類第一次初始化之前）

  • 如果類有分類那么分類的initialize方法會(huì)將類本身的initialize方法替換掉將，（說白了類的initialize方法不會(huì)調(diào)用了 分類的initialize方法會(huì)調(diào)用） 分類的方法執(zhí)行 有且只調(diào)用一次

  • 調(diào)用順序 父類的intialize方法執(zhí)行 子類在執(zhí)行 父類-->子類

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