为什么带有__weak限定符的变量会保留一个对象? [英] Why variable with __weak qualifier retains an object?
本文介绍了为什么带有__weak限定符的变量会保留一个对象?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
这是我的代码:
extern void _objc_autoreleasePoolPrint();
int main(int argc, const char * argv[])
{
NSArray __weak *tmp = nil;
@autoreleasepool {
NSArray __strong *obj = [[NSArray alloc] init];
NSLog(@"obj &: %p", obj);
tmp = obj;
NSLog(@"tmp &: %p", tmp);
_objc_autoreleasePoolPrint();
}
NSLog(@"tmp: %@", tmp); // why not (null) ?
return 0;
}
和控制台输出:
2013-05-01 22:14:32.966 SimpleConsoleObjectiveCApplicationWithARC[40660:f07] obj &: 0x7fedf9403110
2013-05-01 22:14:32.969 SimpleConsoleObjectiveCApplicationWithARC[40660:f07] tmp &: 0x7fedf9403110
objc[40660]: ##############
objc[40660]: AUTORELEASE POOLS for thread 0x7fff751af180
objc[40660]: 2 releases pending.
objc[40660]: [0x7fedf9805000] ................ PAGE (hot) (cold)
objc[40660]: [0x7fedf9805038] ################ POOL 0x7fedf9805038
objc[40660]: [0x7fedf9805040] 0x7fedf9403110 __NSArrayI
objc[40660]: ##############
2013-05-01 22:14:32.971 SimpleConsoleObjectiveCApplicationWithARC[40660:f07] tmp: (
)
PS#1
将NSArray更改为NSMutableArray并将tmp变量设为nil。
Changed NSArray to NSMutableArray and tmp variable became nil.
extern void _objc_autoreleasePoolPrint();
int main(int argc, const char * argv[])
{
NSMutableArray __weak *tmp = nil;
@autoreleasepool {
NSMutableArray __strong *obj = [[NSMutableArray alloc] init];
NSLog(@"obj &: %p", obj);
tmp = obj;
NSLog(@"tmp &: %p", tmp);
_objc_autoreleasePoolPrint();
}
NSLog(@"tmp: %@", tmp);
return 0;
}
有人可以解释一下为什么会这样吗?
Can somebody explain me why it works this way?
推荐答案
似乎 [[NSArray alloc] init]
返回一个共享实例空 NSArray
:
It seems that [[NSArray alloc] init]
returns a "shared instance" of an empty NSArray
:
NSArray *a = [[NSArray alloc] init];
NSArray *b = [[NSArray alloc] init];
NSLog(@"a &: %p", a);
NSLog(@"b &: %p", b);
输出:
a &: 0x100103110
b &: 0x100103110
即使您的强参考<$>此共享实例仍然存在c $ c> obj 消失了,
因此弱指针未设置为 nil
。
This "shared instance" continues to exist even if your strong reference obj
is gone,
therefore the weak pointer is not set to nil
.
显然, [[NSMutableArray alloc] init]
无法返回共享实例。
Obviously, [[NSMutableArray alloc] init]
cannot return a shared instance.
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