Question

注意：这个问题看起来很相似，但不是：When does an associated object get released?

我正在向UIView实例添加第二个描述，如下所示：

- (void) setSecondDescription:(UIView*)view description2:(NSString*)description2 {
    objc_setAssociatedObject (view,&key,description2,OBJC_ASSOCIATION_RETAIN);
}

- (NSString*) secondDescription:(UIView*)view {
    return (id)objc_getAssociatedObject(view, &key);   
}

如果UIView deallocs，关联的描述2是否会被解除分配？有没有办法让这种情况自动发生？

Answer 1

如果您想实际查看整个dealloc时间轴的描述，请参阅WWDC 2011，Session 322,36：22。但是，这是基本的纲要（我想记住它，所以这是我的代码中的实际注释）。

请注意，关联对象在生命周期结束时被释放。

// General Information
// We take advantage of the documented Deallocation Timeline (WWDC 2011, Session 322, 36:22).
// 1. -release to zero
//     * Object is now deallocating and will die.
//     * New __weak references are not allowed, and will get nil.
//     * [self dealloc] is called
// 2. Subclass -dealloc
//     * bottom-most subclass -dealloc is called
//     * Non-ARC code manually releases iVars
//     * Walk the super-class chain calling -dealloc
// 3. NSObject -dealloc
//     * Simply calls the ObjC runtime object_dispose()
// 4. object_dispose()
//     * Call destructors for C++ iVars
//     * Call -release for ARC iVars
//     * Erase associated references
//     * Erase __weak references
//     * Call free()

Answer 2

是。取消分配对象时，将自动释放任何关联对象（使用RETAIN或COPY关联类型）。

Answer 3

简而言之，是 - 当释放拥有对象时，将释放保留的关联对象。请参阅Apple的documentation

的第一部分

Answer 4

Jody Hagins的第4节answer说“擦除相关引用”，这并未明确暗示引用已被释放。所以我使用下面的一段代码（注意WITHOUT ARC）来测试它。

@interface AssociatedObjectHelper : NSObject
@end

@implementation AssociatedObjectHelper
- (void) dealloc
{
    NSLog(@"In %s", __FUNCTION__);
    [super dealloc];
}
@end

@implementation AppDelegate
...
- (void) testReleaseAssociatedObject
{
    static const NSString *key = @"testKey123";
    NSObject *ob = [NSObject new];
    AssociatedObjectHelper *assocOb = [AssociatedObjectHelper new];
    objc_setAssociatedObject(ob, key, assocOb, OBJC_ASSOCIATION_RETAIN);
    [assocOb release];
    [ob release];
}

调用上面的代码确实最终调用 - [AssociatedObjectHelper dealloc]，带有以下堆栈跟踪：

#0  0x000000010000528f in -[AssociatedObjectHelper dealloc]
#1  0x00007fff8a0bb89c in objc_object::sidetable_release(bool) ()
#2  0x00007fff8a0a537f in _object_remove_assocations ()
#3  0x00007fff8a0a1644 in objc_destructInstance ()
#4  0x00007fff8a0a1595 in object_dispose ()
#5  0x00007fff8a0bb89c in objc_object::sidetable_release(bool) ()
#6  0x000000010000e9b6 in -[AppDelegate testReleaseAssociatedObject]

在Xcode 7.0.1上测试

是否会自动发布相关对象？

4 个答案: