我想看一下assign和weak之间的区别。所以我在下面运行这段代码:
@interface Test : NSObject
@property(nonatomic, strong) NSString *str;
@property(nonatomic, assign) NSString *assignString;
@property(nonatomic, weak) NSString *weakString;
@end
@implementation Test
- (id)init
{
self =[super init];
if (self)
{
self.str = @"i'm test string";
self.assignString = self.str;
self.weakString = self.str;
self.str = nil;
NSLog(@"dealloc \nstr = %p\n assignstr = %p\n weakStr = %p\n", self.str, self.assignString, self.weakString);
NSLog(@"str = %@ \nassignStr = %@\n weakString = %@\n", self.str, self.assignString, self.weakString);
}
return self;
}
@end
我认为它应该这样输出:str = 0x0
AssignString = 0x0
weakString = 0x0
str =(空)
AssignString =(空)
weakString =(空)
但是我得到以下输出:
2015-06-17 11:22:04.676 AssignWeakDiff [4696:1897735]
str = 0x0
Assignstr = 0x100002078
weakStr = 0x100002078
str =(空)
AssignStr =我是测试字符串
weakString =我是测试字符串
我的代码有问题吗?
最佳答案
NSObject
子类重复此练习,您将看到传统的对象生命周期行为。 assign
属性的预期输出不正确。您应该期望它有一个指向释放对象的悬挂指针。释放对象时,不会自动将assign
引用设置为nil
。 weak
参考会,但assign
参考不会。 因此,如果您具有如下属性:
@property (nonatomic, strong) MyObject *strongObj;
@property (nonatomic, assign) MyObject *assignObj;
@property (nonatomic, weak) MyObject *weakObj;
然后执行:
self.strongObj = [[MyObject alloc] init];
self.assignObj = self.strongObj;
self.weakObj = self.strongObj;
NSLog(@"%@ %@ %@", self.strongObj, self.assignObj, self.weakObj);
self.strongObj = nil;
NSLog(@"%@ %@ %@", self.strongObj, self.assignObj, self.weakObj);
在第二个
NSLog
语句中,strong
和weak
引用将为nil
,但assign
引用则不是。