Objective-C的内存管理

原则

 内存管理原则：
 1.谁使的引用计数增加，那他也要负责对应的引用计数减少（类似C++，谁new谁delete）
 2.可以对nil的对象release(类似c++允许delete的对象为NULL一样)
 3.当对象引用计数为0时，系统会自动释放该内存
 4.可以借用C++内存管理的经验来控制Objective-C的内存管理

 

• MemoryDemo.h

  //  MemoryDemo.h
  //  MemoryTest
  //
  //  Created by arbboter on 14/11/28.
  //  Copyright (c) 2014ๅนด arbboter. All rights reserved.
  //
  
  #import <Foundation/Foundation.h>
  
  @interface MemoryDemo : NSObject
  {
      NSString*       _objectName;
      int             _objectCount;
  }
  
  -(void)setObjectName:(NSString*)name;
  -(NSString*)getObjectName;
  
  -(void)setObjectCount:(int)count;
  -(int)getObjectCount;
  
  -(void)showInfo;
  
  -(void)dealloc;

• MemoryDemo.m

  //
  //  MemoryDemo.m
  //  MemoryTest
  //
  //  Created by arbboter on 14/11/28.
  //  Copyright (c) 2014年 arbboter. All rights reserved.
  //
  
  #import "MemoryDemo.h"
  
  @implementation MemoryDemo
  
  -(void)setObjectName:(NSString*)name
  {
      /* 对象重复不予重置 */
      if (name != _objectName)
      {
  #if 1
          /* 标准做法 */
          [name retain];
          [_objectName release];
          _objectName = [[NSString alloc] initWithString:name];
          [name release];
  #else
          /* 另一种思路，没想到会出什么问题 */
          [_objectName  release];
          _objectName = [name retain];
  #endif
          
      }
  }
  
  -(NSString*)getObjectName
  {
      return _objectName;
  }
  
  -(void)setObjectCount:(int)count
  {
      _objectCount = count;
  }
  -(int)getObjectCount
  {
      return _objectCount;
  }
  -(void)showInfo
  {
      NSLog(@"name = %@, count = %d", [self getObjectName], [self getObjectCount]);
  }
  
  -(void)dealloc
  {
      [_objectName release];
      [super dealloc];
  }
  
  @end

• main.m

  //
  //  main.m
  //  MemoryTest
  //
  //  Created by arbboter on 14/11/28.
  //  Copyright (c) 2014年 arbboter. All rights reserved.
  //
  
  #import <Foundation/Foundation.h>
  #import "MemoryDemo.h"
  int main(int argc, const char * argv[])
  {
      NSString* name = [[NSString alloc] initWithString:@"Man of pig's feet"];
      NSString* nullName = nil;
      MemoryDemo* mem = [[MemoryDemo alloc] init];
      
      /* nil 允许retian,也允许release */
      [nullName retain];
      [mem setObjectName:name];
      [mem setObjectCount:18];
      [mem showInfo];
      
      // release
      [name release];
      /* nil 允许retian,也允许release */
      [nullName release];
      
      // OK!
      [mem showInfo];
      
      [mem release];
  
  #if 0
      /* error, mem's value is not nil but
       * mem's retain count alreadly to be 0
       */
      [mem release];
  #endif
      
      return 0;
  }
  
  /**
   * 内存管理原则：
   * 1.谁使的引用计数增加，那他也要负责对应的引用计数减少（类似C++，谁new谁delete）
   * 2.可以对nil的对象release(类似c++允许delete的对象为NULL一样)
   * 3.当对象引用计数为0时，系统会自动释放该内存
   * 4.可以借用C++内存管理的经验来控制Objective-C的内存管理
   */