weakSelf在被阻止之前被解除分配

Question

So somehow my weakSelf variable is being deallocated before my block has a chance to execute. This only happens in one specific scenario, the other times I hit this block it works fine. Here's what my code looks like:

__weak typeof(self) weakSelf = self;
DBTEligibleAccountFetcher *accountFetcher = [[DBTEligibleAccountFetcher alloc] init];
NSArray *eligibleDepositAccounts = [accountFetcher fetchDepositEligibleAccounts];
if(eligibleDepositAccounts.count == 1) {
    DBTDepositAmountLimitsHandler *limitChecker = [[DBTDepositAmountLimitsHandler alloc] init];
    [limitChecker handleRequest:self.navigationController bankAccount:eligibleDepositAccounts.firstObject completionBlock:^(DBDepositCheckAccountLimits *limitDetails) {
        containerController.limitDetails = limitDetails;
        [weakSelf.navigationController handleNewRootPush:containerController withCompletion:completionBlock animated:YES];
    }];
} else {
    [self.navigationController handleNewRootPush:containerController withCompletion:completionBlock animated:YES];
}

By the time it gets to the weakSelf.navigationController... line, weakSelf is nil. I'm not sure how to even debug this or how the variable could get deallocated before it is even used.

Does anyone know any scenarios that could be going on right now? Or any tips on how I might go about debugging this issue?

Answer 1

Let's say you have a view controller, the user taps a button, therefore you send some information to the server asynchronously and you are prepared to handle when the request comes back. Meanwhile your user switches to another view and your view controller gets deallocated before your method returns.

First consider what you want to happen. Sometimes a request has become pointless if the view controller is gone. Say you have a site that translates German to French. If the translation comes back and your view controller is gone, you just ignore the result. But if you have to process the result, whether the view controller is there or not, then you need to rearrange your code so that it works even if the view controller is nil because the user switched to a different view.