何时弱到何时对块中的嵌套块进行强引用

Question

I am looking for retain cycles in my block in my code. I have the following code in my UITableViewController :

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    //[...] Not important code.
    __weak ELParkingLocationTVC *weakself = self; // Required? (1)
    cell.completionBlock = ^ {
        __strong ELParkingLocationTVC *strongSelf = weakself; // Required? (2)
        __weak ELParkingLocationTVC *weak2self = weakself; // Required? (3)
        [strongSelf dismissViewControllerAnimated:YES completion:^{
            __strong ELParkingLocationTVC *strong2self = weak2self; //Required? (4)
            ELMenuHistoryTVC *menuTVC = [strong2self.navigationController.viewControllers firstObject];
            [menuTVC.parentTabBarController moveToTab:ELMapViewControllerIndex completion:^(BOOL finished) {
                ElMainMapViewController *mainMapViewController = menuTVC.parentTabBarController.viewControllers[ELMapViewControllerIndex];
                //ELCustomParkplace *customParkplace = [strong2self parkplaceAtIndex:indexPath.row]; //(5)
                [mainMapViewController moveToCoordinate:customParkplace.coordinate];
            }];
        }];
    };
}

And have the following questions:

1. Which __weak and which __strong reference do I need? I am sure that 1st and 2nd I have to use, but I am really not sure about 3rd and 4th.
2. Can I use @strongify and @weakify here?
3. I think I don't need line (5), but I am not sure.

Any suggestion, link or nice comment will be appreciated!

Answer 1

You do need a weak reference for the cell completion handler, because you have a reference cycle: self > UITableView > UITableViewCell > self .

You do not need to use the __strong qualifier. Variables are strong references by default.

You do not need a weak reference for the animation and transition completion handlers, as those blocks are released as soon as the transition completes, but in this case they can't use self because they're nested inside of a block that can't capture self .

So keep weakSelf and strongSelf , and use the same strongSelf variable inside all of the nested blocks.