Objective-C lesson 2 内存管理－自动释放池的工作过程

//
//  main.m
//  RetainCount
//
//  Created by Waqar Malik on 3/30/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface RetainTracker : NSObject
@end // RetainTracker

@implementation RetainTracker

- (id) init
{
    if (self = [super init])
    {
        NSLog (@"init: Retain count of %lu.", [self retainCount]);
    }
    
    return (self);
} // init


- (void) dealloc
{
    NSLog (@"dealloc called. Bye Bye.");
    [super dealloc];
} // dealloc

@end // RetainTracker

int main(int argc, const char * argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    
    RetainTracker *tracker = [RetainTracker new]; // count: 1
    
    [tracker retain]; // count: 2
    [tracker autorelease]; // count: still 2
    [tracker release]; // count: 1
    
    NSLog (@"releasing pool");
    [pool release]; 
    // gets nuked, sends release to tracker
    
    //autoreleasepool
    
        RetainTracker *tracker2 = [RetainTracker new]; // count: 1
        
        [tracker2 retain]; // count: 2
        [tracker2 autorelease]; // count: still 2
        [tracker2 release]; // count: 1
        
        NSLog (@"auto releasing pool");

    //autoreleasepool

return (0); }



运行结果：
init: Retain count of 1.
releasing pool
dealloc called.Bye Bye.
你可能已经猜到，释放自动释放池之前的NSLog函数比RetainTracker类中的NSLog()函数先被调用。


PS:还有一点大家需要注意,就是清理自动释放池，比如下面的代码：

int i;
    for (i = 0; i < 1000000; i++) {
        id object = [someArray objectAtIndex: i];
        NSString *desc = [object description];
        // and do something with the description
    }

这个循环创建了100万个字符串对象，所有这些对象都被放进当前自动释放池的话就会产生100万个闲置的字符串，并一直存在直到自动释放池销毁时才释放。解决方法如下面的代码：

 NSAutoreleasePool *pool;
    pool = [[NSAutoreleasePool alloc] init];
    
    int i;
    for (i = 0; i < 1000000; i++) {
        id object = [someArray objectAtIndex: i];
        NSString *desc = [object description];
        // and do something with the description
        if (i % 1000 == 0) {
            [pool release];
            pool = [[NSAutoreleasePool alloc] init];
        }
    }
    [pool release];

 

循环每执行1000次，新的自动释放池就被销毁，同时有一个更新的被创建。

 

请注意，如果开发iPhone软件，则不能使用垃圾回收。实际上，在编写iPhone程序时，苹果公司建议你不要在自己的代码中使用autorelease方法，同时还要避免使用创建自动释放对象的便利函数。