施用属性和直接使用变量

   假设[NSArray arrayWithObjects:[NSMutableString stringWithString:@"MutableString"],@"string", nil]为对象A

   MyViewController *myVC=[[MyViewController alloc]init];

    myVC.myArray=[NSArray arrayWithObjects:[NSMutableString stringWithString:@"MutableString"],@"string", nil];

// A retaincount ＋1 变为 2

    NSLog(@"retain count -> %d", [myVC.myArray retainCount]);

2013-02-15 10:36:43.749 MyTest[2039:c07] retain count -> 3

   MyViewController *myVC=[[MyViewController alloc]init];

// A retaincount ＋1 变为 2

    }// A retaincount －1 变为 1
    //_array=myVC.myArray;
    self.array=myVC.myArray;// A retaincount ＋1 变为 2

    NSLog(@"retain count -> %d", [myVC.myArray retainCount]);

   MyViewController *myVC=[[MyViewController alloc]init];

// A retaincount ＋1 变为 2

    }// A retaincount -1 变为 1
    _array=myVC.myArray; // A retaincount 为 1
    //self.array=myVC.myArray;

    NSLog(@"retain count -> %d", [myVC.myArray retainCount]);