Object-C中管理内存

最新推荐文章于 2024-10-16 01:08:45 发布

最新推荐文章于 2024-10-16 01:08:45 发布 · 61 阅读

本文详细介绍了Objective-C中对象的保留管理机制，包括如何使用`retain`、`release`方法调整对象引用计数，以及对象如何在计数降至0时自动进行内存回收。通过实例展示了对象创建、保留计数的增减、手动释放对象及其影响。

Object-C之中采用一种保留记录的方式记录我们所创建的所有的对象，并且，当该计数减少为0的时候，Object-C自动收回分配给一个对象的内存。

Text *text1 = [[Text alloc]init];
Text *text2 = [[Text alloc]init];

每一个对象的计数都为1，我们可以通过retainCount方法对其进行输出，如

printf("text1 retain count is %d",[text1 retainCount]);

retain为增加保留计数的方法，可以直接显式的进行调用

[text1 retain];

例：retaincount.m

#import <Foundation/Foundation.h>
#import <stdio.h>
@interface Class1:NSObject
@end
@implementation Class1
@end
int main(void)
{
  Class1 *object1 = [[Class1 alloc]init];
  Class1 *object2 = [[Class1 alloc]init];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("object2 retain count:%i\n",[object2 retainCount]);
  return 0;
}

结果为

object1 retain count:1
object2 retain count:1

其中我们可以通过手动的增加或者减少保留计数来对对象进行管理
例：incrementcount.m

#import <Foundation/Foundation.h>
#import <stdio.h>
@interface Class1:NSObject
@end
@implementation Class1
@end
int main(void)
{
  Class1 *object1 = [[Class1 alloc]init];
  Class1 *object2 = [[Class1 alloc]init];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("object2 retain count:%i\n",[object2 retainCount]);
  [object1 retain];
  [object1 retain];
  [object2 retain];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("object2 retain count:%i\n",[object2 retainCount]);
  return 0;
}

结果为

object1 retain count:1
object2 retain count:1
object1 retain count:3
object2 retian count:2

例：decrementcount.m

#import <Foundation/Foundation.h>
#import <stdio.h>
@interface Class1:NSObject
@end
@implementation Class1
@end
int main(void)
{
  Class1 *object1 = [[Class1 alloc]init];
  Class1 *object2 = [[Class1 alloc]init];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("object2 retain count:%i\n",[object2 retainCount]);
  [object1 retain];
  [object1 retain];
  [object2 retain];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("object2 retain count:%i\n",[object2 retainCount]);
  [object1 release];
  [object2 release];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("objcet2 retian count:%i\n",[object2 retainCount]);
  return 0;
}

结果为

object1 retain count:1
object2 retain count:1
object1 retain count:3
object2 retian count:2
object1 retain count:2
object2 retain count:1

当对象的保留技术达到0的时候，object-c从内存中收回对象
例：dealloc.m

#import <Foundation/Foundation.h>
#import <stdio.h>
@interface Class1:NSObject
@end
@implementation Class1
@end
int main(void)
{
  Class1 *object1 = [[Class1 alloc]init];
  Class1 *object2 = [[Class1 alloc]init];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("object2 retain count:%i\n",[object2 retainCount]);
  [object1 retain];
  [object1 retain];
  [object2 retain];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("object2 retain count:%i\n",[object2 retainCount]);
  [object1 release];
  [object2 release];
  printf("object1 retain count:%i\n",[object1 retainCount]);
  printf("objcet2 retian count:%i\n",[object2 retainCount]);
  [object1 release];
  [object1 release];
  [object2 release];
  return 0;
}

结果为

object1 retain count:1
object2 retain count:1
object1 retain count:3
object2 retian count:2
object1 retain count:2
object2 retain count:1
Deallocing the object
Deallocing the object

object中还存在着自动释放池的概念，对于不是使用alloc或new创建的对象，我们可以让object-c使用自动释放池管理。

简单的说，就是如果创建一个对象，那么再释放对象的时候，对象中的所有属性也会同时一并被释放。

例

#import <Foundation/Foundation.h>
#import <stdio.h>
int main()
{
  NSAutoreleasePool *pool = 
    [[NSAutoreleasePool alloc]init];
  NSString *string1 = [NSString
    stringWithString:@"Pool-managed string"];
  printf("%s's retain count:%x\n",[string1 cString],
  [string1 retainCount]);
  [pool release];
  return 0;
}