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 */