OC内存管理黄金法则&＃xff08;译文&＃xff09;&＃xff1a;如果一个对象使用了alloc&＃xff0c;[mutable]copy&＃xff0c;retain&＃xff0c;那么你必须使用相应的release或者autorelease释放。
Xcode建立Command Line Tool项目&＃xff1a;DogSample&＃xff0c;选择手动管理内存&＃xff0c;并添加Dog和Person类。
Dog有唯一标识的ID属性&＃xff0c;Dog.h代码&＃xff1a;
#import
{int _ID;
}&＃64;property int ID;&＃64;end
添加对象retainCount&＃61;0时自动调用的dealloc 函数&＃xff0c;Dog.m代码&＃xff1a;
#import "Dog.h"&＃64;implementation Dog&＃64;synthesize ID &＃61; _ID;- (void) dealloc
{NSLog(&＃64;"Dog %d is dealloc ...", _ID);[super dealloc];
}&＃64;end
Person对象有Dog属性&＃xff0c;表示某某人拥有某某狗&＃xff0c;Person.h
#import
#import "Dog.h"&＃64;interface Person : NSObject
{Dog *_dog;
}- (void) setDog:(Dog *)newDog;
- (Dog *) dog;&＃64;end
同样&＃xff0c;Person.m代码如下&＃xff1a;
#import "Person.h"
#import "Dog.h"&＃64;implementation Person- (void) setDog:(Dog *)newDog;
{//暂时不写
}- (Dog *) dog
{return _dog;
}- (void) dealloc
{NSLog(&＃64;"Person is dealloc ...");[super dealloc];
}&＃64;end
下面我们来看main.m的实现&＃xff0c;首先创建一条狗狗和人类小丽&＃xff0c;我们用 [xiaoLi setDog:dog1]; 表示小丽拥有dog1
#import
#import "Dog.h"
#import "Person.h"int main(int argc, const char * argv[])
{&＃64;autoreleasepool {//NSLog(&＃64;"Hello, World!");
Dog *dog1 &＃61; [[Dog alloc] init];[dog1 setID:1];Person *xiaoLi &＃61; [[Person alloc] init];//小丽拥有狗狗 dog1
[xiaoLi setDog:dog1];}return 0;
}
那么Person.m的setDog函数具体该如何实现呢&＃xff1f;画图分析&＃xff1a;
1.我们需要把 dog1赋值给xiaoLi对象的_dog属性&＃xff0c;让小丽拥有dog1
2.所以dog1指向的对象其现在应该是reatainCount&＃61;2了&＃xff0c;所以setDog函数添加如下代码&＃xff1a;
if(newDog !&＃61; _dog){_dog &＃61; [newDog retain];
}
现在假设我们release人类xiaoLi&＃xff0c;那么Dog的retainCount&＃61;1还是retainCount&＃61;2 &＃xff1f;&＃xff1f;我们写一下代码测试&＃xff1a;
[xiaoLi release];NSLog(&＃64;"xiaoli release, dog1 retainCount is %lu", [dog1 retainCount]);
运行结果&＃xff1a;
Person is dealloc ...
xiaoLi release, Dog retainCount is 2
引用计数器仍然是2&＃xff0c;说明当我们释放xiaoLi的时候&＃xff0c;并没有因为_dog属性指向Dog对象的关系而自动执行 [dog1 retain]&＃xff0c;而是需要我们手动去实现&＃xff1a;
- (void) dealloc
{NSLog(&＃64;"Person is dealloc ...");//添加代码&＃xff1a;需要手动使Dog的retainCount减1
[_dog release];[super dealloc];
}
这时候的内存示意图如下&＃xff1a;
点击这里下载源代码
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