转:http://tigercat1977.blog.163.com/blog/static/2141561122012111294616203/
第六讲:Obj-C 内存管理4 - 自动释放池
什么是自动释放池
自动释放池的好处
如何创建一个自动释放池
自动释放池如何释放对象内存
自动释放池栈式结构管理
Autorelease pool
1. 自动释放池(Autorelease Pool)是 OC 的一种内存自动回收机制,可以将一些临时变量通过自动释放吃来回收统一释放
2. 当自动释放池本身销毁的时候,池子里所有的对象都会做一次 release 操作
autorelease
任何OC对象只要调用 autorelease 方法,就会把该对象放大离自己最近的自动释放池中(栈顶的释放池)
创建自动释放池 (两种方法)
@ autoreleasepool
{
}
IOS5.0 之前的老方式
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[pool release];
遛狗原理
典型例子(正确)
Dog *dog1 = [[Dog alloc] init];
[xiaoLi setDog:dog1];
[dog1 release];
典型例子 (错误)
[xiaoLi setDog:[[Dog alloc] init]];
上述代码有内存泄漏
典型例子(正确)好的方法
Dog *dog = [[[Dog alloc] init] autorelease];
[xiaoLi setDog:dog1];
//这里不能跟 [dog1 release];
典型例子(正确) 放成一行
[xiaoLi setDog:[[[Dog alloc] init] autorelease]];
黄金法则
如果对一个对象使用了 alloc, [mutable]copy, retain,那么必须使用相应的 release 或者 autorelease
举例
// Dog.h #import <Foundation/Foundation.h> @interface Dog : NSObject { int _ID; } @property int ID; @end
// Dog.m #import "Dog.h" @implementation Dog @synthesize ID = _ID; - (void) dealloc { NSLog(@"dog %d dealloc", _ID); [super dealloc]; } @end
// Person.h #import <Foundation/Foundation.h> #import "Dog.h" @interface Person : NSObject { Dog *_dog; } @property (retain) Dog *dog; @end
// Person.m #import "Person.h" @implementation Person @synthesize dog = _dog; - (void) dealloc { self.dog = nil; NSLog(@"person dealloc"); [super dealloc]; } @end
// main.m #import <Foundation/Foundation.h> #import "Person.h" #import "Dog.h" int main (int argc, const char * argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSLog(@"Hello, World!"); Person *xiaoLi = [[Person alloc] init]; Dog *dog1 = [[[Dog alloc] init] autorelease]; // 把 dog1 这条狗放在自动释放池里,上边的pool中 NSLog(@"dog1 retaincount is %ld", [dog1 retainCount]); xiaoLi.dog = dog1; NSLog(@"dog1 retaincount2 is %ld", [dog1 retainCount]); // [dog1 release]; // autorelease 了,不需要再 release [xiaoLi release]; NSLog(@"dog1 retaincount3 is %ld", [dog1 retainCount]); [pool release]; NSLog(@"end of release"); return 0; } /* 输出结果 Hello, World! dog1 retaincount is 1 dog1 retaincount2 is 2 person dealloc dog1 retaincount3 is 1 dog 0 dealloc end of release */