CODEWITHSUNDEEP
objective-ccocoa-touchexceptiontry-catch
Tieme
Tieme

Reputation: 65409

Why use Try/Catch instead of testing for an NSError

Sometimes you see a piece of iOS - Objective-C code use a Try/Catch structure.

For example this example from: http://docs.xrtml.org/2-1-0/pubsub/ios/ortcclient.html

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Instantiate OrtcClient
    ortcClient = [OrtcClient OrtcClientWithConfig:self];

    // Post permissions
    @try {
        NSMutableDictionary* myPermissions = [[NSMutableDictionary alloc] init];

        [myPermissions setObject:@"w" forKey:@"channel1"];
        [myPermissions setObject:@"w" forKey:@"channel2"];
        [myPermissions setObject:@"r" forKey:@"channelread"];

        BOOL result = [ortcClient saveAuthentication:@"http://ortc-developers.realtime.co/server/2.1/" isCLuster:YES authenticationToken:@"myAuthenticationToken" authenticationTokenIsPrivate:NO applicationKey:@"myApplicationKey" timeToLive:1800 privateKey:@"myPrivateKey" permissions:myPermissions];

        if (result) {
            // Permissions correctly posted
        }
        else {
            // Unable to post permissions
        }
    }
    @catch (NSException* exception) {
        // Exception posting permissions
    }

    // Set connection properties
    [ortcClient setConnectionMetadata:@"clientConnMeta"];
    [ortcClient setClusterUrl:@"http://ortc-developers.realtime.co/server/2.1/"];

    // Connect
    [ortcClient connect:@"myApplicationKey" authenticationToken:@"myAuthenticationToken"];
}

Why use such a structure, couldn't you just check for an NSError (indirect) return from the saveAuthentication:isCLuster:authenticationToken:... method like 'regular' Cocoa-Touch code does? For example when reading JSON:

NSError *error = nil;
id result = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&error];

if (error == nil){
    NSLog(@"%@", result);
}else{
    NSLog(@"%@", [error localizedDescription]);
}

Upvotes: 1

Views: 509

Answers (2)

zahreelay
zahreelay

Reputation: 1742

Use try catch where you expect a condition that cannot be recovered from or which may lead to an undefined behaviour such as crash, use NSError where recovereable errors are expected like wrong values from a json object or xml.

You can go throughApple documentation about exception programming.

Upvotes: 3

Jeroen Vuurens
Jeroen Vuurens

Reputation: 1251

In general, try-catch is more robust, does not require you to define an exact position of where to test (could be a block) and provides info about the exception.

Upvotes: 0

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