objective-c - 使用工厂方法设置 __weak 变量似乎会使对象保持事件时间过长

Question

我创建了一个 Person 类，我在其中实例化了两个对象:

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        Person * __weak pweak = [Person new];
        Person *p = [Person personWithName:@"Strong" lastName:nil dateOfBirth:nil];
    }
    return 0;
}

Person 类重写了它的 dealloc 方法，因此它打印了被释放的 Person 的名字。

一切都按预期进行，弱变量不会使 Person 实例保持事件状态，我在日志中看到了这一点(“John”是 Person 的默认名称> 对象):

2013-01-23 17:36:51.333 Basics[6555:303] John is being deallocated
2013-01-23 17:36:51.335 Basics[6555:303] Strong is being deallocated

但是，如果我在对弱变量的赋值中使用工厂方法:

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        Person * __weak pweak = [Person personWithName:@"Weak" lastName:nil dateOfBirth:nil];
        Person *p = [Person personWithName:@"Strong" lastName:nil dateOfBirth:nil];
    }
    return 0;
}

这是我看到的日志:

2013-01-23 17:44:16.260 Basics[6719:303] Strong is being deallocated
2013-01-23 17:44:16.262 Basics[6719:303] Weak is being deallocated

我做错了什么吗？

可能关注Person类的这些方法:

- (id)initWithName:(NSString *)name lastName:(NSString *)lastName dateOfBirth:(NSDate *)birth {
    self = [super init];
    if (self) {
        _name = name;
        _lastName = lastName;
        _dateOfBirth = birth;
    }
    return self;
}

+ (id)personWithName:(NSString *)name lastName:(NSString *)lastName dateOfBirth:(NSDate *)birth {
    return [[self alloc] initWithName:name lastName:lastName dateOfBirth:birth];
}

Answer 1

当你通过 alloc/init 方法分配一个对象时，ARC 赋予了对象的创建者稍后释放它的责任(所以当你将一个对象存储为 __strong 时，它会一直存在直到有人拥有它，当您将它存储为 __weak 时，它会被释放，因为没有人拥有它。

来自 Apple 文档 ( http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/memorymgmt/Articles/mmRules.html#//apple_ref/doc/uid/20000994-BAJHFBGH )

You own any object you create You create an object using a method whose name begins with “alloc”, “new”, “copy”, or “mutableCopy” (for example, alloc, newObject, or mutableCopy).

在处理工厂方法时，ARC 将返回变量视为自动释放，因此当池被耗尽时它们将被释放。实际上，ARC 将您的工厂方法转换为:

+ (id)personWithName:(NSString *)name lastName:(NSString *)lastName dateOfBirth:(NSDate *)birth 
{
   return [[[self alloc] initWithName:name lastName:lastName dateOfBirth:birth] autorelease];
}