Objective-C 内存管理

首先申明下，本文为笔者学习《Objective-C 基础教程》的笔记，并加入笔者自己的理解和归纳总结。

1、引用计数法

Objective-C采用引用计数的技术，当访问一个对象时，该对象的保留计数器值加一。当结束对象访问时，将对象的保留计数器值减一。
当使用alloc、new方法或者通过copy创建一个对象时，对象的保留计数器值被设置为1。要增加保留计数器值，调用retain方法，要减少的话，调用release方法。
当一个对象的保留计数器值归零时，会调用dealloc方法。

@interface Shape : NSObject@end@implementation Shape- (id) init {if (self = [super init]) {NSLog(@"Shape init retainCount = %lu", [self retainCount]);}return self;}- (void) dealloc{NSLog(@"Shape dealloc called");[super dealloc];}@endint main(int argc, const char* argv[]) {Shape* shape = [Shape new];[shape retain]; // retainCount = 2NSLog(@"Shape retainCount = %lu", [shape retainCount]);[shape release]; // retainCount = 1NSLog(@"Shape retainCount = %lu", [shape retainCount]);[shape retain]; // retainCount = 2NSLog(@"Shape retainCount = %lu", [shape retainCount]);[shape release]; // retainCount = 1NSLog(@"Shape retainCount = %lu", [shape retainCount]);[shape release]; // retainCount = 0return 0;}

2、自动释放池

自动释放池是用来存放对象的集合，并且能够自动释放。
(1) 创建自动释放池
通过@autoreleasepool关键字
通过NSAutoReleasePool对象
(2) autorelease方法
将对象添加到自动释放池，当自动释放池销毁时，会向池中对象发送release消息。

- (id) autorelease;

(3) 简单例子

int main(int argc, const char* argv[]) {NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];Shape* shape = [Shape new]; // retainCount = 1[shape retain]; // retainCount = 2[shape autorelease]; // retainCount = 2NSLog(@"Shape retainCount = %lu", [shape retainCount]);[shape release]; // retainCount = 1NSLog(@"releaseing pool");[pool release];@autoreleasepool {Shape* shape = [Shape new]; // retainCount = 1[shape retain]; // retainCount = 2[shape autorelease]; // retainCount = 2NSLog(@"Shape retainCount = %lu", [shape retainCount]);[shape release]; // retainCount = 1NSLog(@"releaseing pool");}return 0;}

3、自动引用计数ARC

启动ARC以后，编译器会帮你插入retain和release语句，就像自己手动写好了所有的内存管理代码。
在项目的Build Settings选项卡中，启动ARC，默认是YES的。

启动ARC后，不能调用对象的内存管理方法：

• retain
• retainCount
• release
• autorelease
• dealloc