最近Appleのドキュメントに従った後

保持サイクルの問題を回避するために、次の規則を使用しました。

__weak __typeof(self) weak_self = self;
void(^completionBlock)(void) = ^(){

    __typeof(self) strong_self = weak_self;
    if (strong_self) {

        if (strong_self->_completion != NULL) {
            strong_self->_completion();
        }
    }
};

しかし、ブロックを呼び出す前に自己の割り当てが解除されているため、このコードはクラッシュしていることがわかりました。

私が以下を使用したとき、それは機能していることがわかりました。

__block __typeof(self) block_self = self;
void(^completionBlock)(void) = ^(){

     if (block_self->_completion != NULL) {
         block_self->_completion();
     }
};

__weak参照をいつ使用すべきか混乱しています。次の「self.completionBlock」の場合のみ

__weak __typeof(self) weak_self = self;
self.completionBlock = ^(){

     if (weak_self->_completion != NULL) {
         weak_self->_completion();
     }
};

この条件に関するどんな光も私にとって非常に役に立ちます。

私の実装コードを以下に示します。

=================================================

ファイルMyViewController

@implementation MyViewController

//starting point 
- (void)myPushMethod {
    __weak __typeof(self) weak_self = self;
    MyViewControllerTransitioning *delegateObj = [[MyViewControllerTransitioning alloc] initWithCompletion:^{

        //resetting the delegate
        __typeof(self) strong_self = weak_self;
        if (strong_self) {
            strong_self.navigationController.delegate = nil;
        }
    }];
    self.navigationController.delegate = delegateObj;
    [self.navigationController pushViewController:someViewController animated:_animated];
    //it is found that delegateObj is getting deallocated while reaches this point
}

@end

=================================================

ファイルMyViewControllerTransitioning

@implementation MyViewControllerTransitioning

- (instancetype)initWithCompletion:(completionHandler)completionHandler
{
    if(self = [super init])
    {
        if (completionHandler != NULL) {
            _completion  = completionHandler;
        }
    }
    return self;
}

- (id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC
{
    id<UIViewControllerAnimatedTransitioning> animationTransitioning = nil;

    //crashes here
    __block __typeof(self) block_self = self;
    void(^completionBlock)(void) = ^(){

        if (block_self->_completion != NULL) {
            block_self->_completion();
        }
    };

    //showing presentation-up animation if Push
    if (operation == UINavigationControllerOperationPush) {
        animationTransitioning = [[MyAnimator alloc] initWithAnimationCompletion:completionBlock];
    }
    return animationTransitioning;
}

- (void)dealloc{
//dealloc is called before invoking completionBlock
}

@end

=================================================

ファイルMyAnimator

@implementation MyAnimator

- (instancetype)initWithAnimationCompletion:(presentationUpCompletion)completionHandler
{
    if(self = [super init])
    {
        if (completionHandler != NULL) {
            _completion  = completionHandler;
        }
    }
    return self;
}

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext
{
    return my_duration;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {

    //animation logic

    [UIView animateWithDuration:duration animations: ^{
        //animation logic
    } completion: ^(BOOL finished) {
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];
}

- (void)animationEnded:(BOOL) transitionCompleted {
    if (transitionCompleted && _completion != NULL) {
        _completion();
    }
}

@end