组合与聚合

1类与对象（续）
1.1dealloc方法
1.1.1该方法是从NSObject类中欧诺个继承的
1.1.2该方法在对象的堆空间被释放之前由ARC调用
2.组合与聚合
2.1是指两个（或以上）类之间的一种关系
2.2是（一个）整体类与（多个）部分类之间的关系
2.3组合是强关系，即同生共死

2.3聚合是弱关系，非同生共死
习题
TRAnimal.h

#import <Foundation/Foundation.h>
#import "TRHead.h"
#import "TRLimb.h"
#import "TRTrunk.h"
NS_ASSUME_NONNULL_BEGIN
@interface TRAnimal : NSObject
{
    TRHead *_head;
    TRLimb *_limb;
    TRTrunk *_trunk;
}
@end

TRAnimal.m

#import "TRAnimal.h"

@implementation TRAnimal
-(instancetype)init
{
    self = [super init];
    if(self)
    {
        NSLog(@"动物诞生了");
        _head = [[TRHead alloc] init];
        _limb = [[TRLimb alloc] init];
        _trunk =[[TRTrunk alloc]init];
    }
    return self;
}
-(void)dealloc
{
    NSLog(@"动物死亡了");
}
@end

ViewController.m

#import "ViewController.h"
#import "TRAnimal.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    TRAnimal *a = [[TRAnimal alloc] init];
    NSLog(@"--------");
}

2.4聚合是弱关系，非同生共死
TRAnimal.h

#import <Foundation/Foundation.h>
#import "TRHead.h"
#import "TRLimb.h"
#import "TRTrunk.h"
NS_ASSUME_NONNULL_BEGIN

@interface TRAnimal : NSObject

@property TRHead *head;
@property TRLimb *limb;
@property TRTrunk *trunk;
    

@end

TRAnimal.m

#import "TRAnimal.h"

@implementation TRAnimal
-(instancetype)init
{
    self = [super init];
    if(self)
    {
        NSLog(@"动物诞生了");

    }
    return self;
}
-(void)dealloc
{
    NSLog(@"动物死亡了");
}
@end

ViewController.m

#import "ViewController.h"
#import "TRAnimal.h"
@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    TRHead *h = [[TRHead alloc] init];
    TRLimb *l = [[TRLimb alloc] init];
    TRTrunk *t = [[TRTrunk alloc] init];
    NSLog(@"------");
    {
        TRAnimal *a = [[TRAnimal alloc] init];
        a.head = h;
        a.limb = l;
        a.trunk = t;
    }
    NSLog(@"=======");
}