Copying from "id" variable

Question

I have created a class NetCalculator which I am calling when a button is pressed. The method calculate network it gets 2 NSStrings and returns an id object (either "Network" object or "UIAlertView". Then I am checking which object is and I present the data. When I am using the UIAlertView the app is crashing after showing 2-3 alerts.

Any ides why this happens? On terminal it doesnt show any error just some random hexadecimal.

-(IBAction)calculate:(id)sender {
    id result;

    Network *network = [[Network alloc]init];

    NetCalculator *netCalculated = [[NetCalculator alloc] init];
    result = [netCalculated calculateNetworkWithIP:ipLabel.text andSubnet:subnetLabel.text];

    if([result isKindOfClass:[Network class]]){
        network = result;
        NSLog(@"network %@",network.networkIP);    
    }

    else if([result isKindOfClass:[UIAlertView class]]) {

        UIAlertView *alert;
        alert = result;

        [alert show];    
    }
};

the issue seems to be that it is deallocated randomly in the bg.. well at least in 99% of those cases that is the issue — Daij-Djan, Dec 29 '13 at 20:25
@op please show where you create the alert and where you retain/release it -- are you using arc or mrc? — Daij-Djan, Dec 29 '13 at 20:26
@sha I did an nslog ">" at flexaddicted Do you mean that my class is wrong? I mean is it wrong to return an alertview if something went wrong? — BlackM, Dec 29 '13 at 20:30
@Daij-Djan the alert is created inside the NetworkCalculator Class that way: "UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@...." and then I return that. — BlackM, Dec 29 '13 at 20:32
and Right after alloc/init it is shown? once? or n times? Create-Show-Create-Show works Create-show-show doesn't. — Daij-Djan, Dec 29 '13 at 20:36
I am returning it and then I am checking what kind of class it is (check it on my code). It's shows ok but after pressing ok is crashing — BlackM, Dec 29 '13 at 20:44
@JoshValdivieso If `[result isKindOfClass:[UIAlertView class]]` evaluates to true, then the UIAlertView object is initialized correctly. — Aaron Brager, Dec 29 '13 at 20:58

score 0 · Accepted Answer · edited May 23 '17 at 12:11

Your code is quite strange to me. Your method calculateNetworkWithIP could return a Network result or a UIAlertView result. I wouldn't follow such an approach.

If the problem relies on memory you should show us hot that method is implemented.

Anyway, I would propose some changes (The following code does not take into account ARC or non ARC code). In particular, I would modify the calculateNetworkWithIP to return a Network result. An error will populated if a problem arises and it is passed as an argument.

- (Network*) calculateNetworkWithIP:(NSString *)ip subnet:(NSString*)subnet error:(NSError**)error

If all is ok, the result would be be a Network and so print it or reused it somewhere. Otherwise an NSError would be returned and based on that create and show an alert view.

So, here pseudo code to do it.

NetCalculator *netCalculated = [[NetCalculator alloc] init];

NSError* error = nil;
Network* networkResult = [netCalculated calculateNetworkWithIP:ipLabel.text subnet:subnetLabel.text error:&error];

if(error != nil) {
    // create and show an alert view with the error you received
} else {
    // all ok so, for example, save the result in a instance variable
}

To follow a similar approach you can take a look at why is "error:&error" used here (objective-c).

Your answer looks good but since I am unfamiliar with creating my own NSErrors what should my method return in case of error? The method expects Network object so I will return nil? Also how I will pass the error in the "error" variable? — BlackM, Dec 29 '13 at 23:42
I tried returning nil and initializing the error in the NetworkCalculator by doing this: error = [[NSError alloc] initWithDomain:@"some error" code:5 userInfo:nil]; but the "error" is still nil in the main — BlackM, Dec 30 '13 at 00:06
I found the problem. I was using NSError instead of NSError*. Thank you — BlackM, Dec 30 '13 at 00:17

Copying from "id" variable

1 Answers1