CODEWITHSUNDEEP
objective-cmultithreadingmacoscocoa
Dmitri K.
Dmitri K.

Reputation: 197

Block gets executed twice on async thread

I have a weird issue. I have a class that calls a method in another class on a background thread, but it fetches data twice on Thread 2 and then once it finishes puts it to thread 4 for example. Does anyone know why?

Class that calls the method:

-(void)awakeFromNib
{
    NSString *swedbankRate;

    CurrencyViewHelper *currencyRates = [[CurrencyViewHelper alloc]init];

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        swedbankRate = [currencyRates getSwedbankRates];
        NSLog(@"%@", swedbankRate);
    });

So the part from the CurrencyViewHelper is:

-(NSString *)getSwedbankRates {

// Set to empty String in case there is some issue
swedbankRate = @"";

// Get Data from Swedbank
NSString *swedbankURL = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"https://www.swedbank.ee/private/d2d/payments2/rates/currency?language=EST"]
                                                 encoding:NSASCIIStringEncoding
                                                    error:nil];
NSArray *swedbankArray = [swedbankURL componentsSeparatedByString:@"<tr>"];
NSString *swedbankString = swedbankArray[18];
swedbankArray = [swedbankString componentsSeparatedByString:@"<tr>"];

NSString *swedbankDirty = swedbankArray[0];

// Check if the fetched data corresponds to RUB data
if ([swedbankDirty containsString:@"RUB"]) {

    swedbankDirty = [swedbankDirty stringByReplacingOccurrencesOfString:@"<td class=\"numeric-cell\">"
                                                             withString:@""];
    swedbankDirty = [swedbankDirty stringByReplacingOccurrencesOfString:@"\n"
                                                             withString:@""];
    swedbankDirty = [swedbankDirty stringByReplacingOccurrencesOfString:@" "
                                                             withString:@""];
    NSArray *swedbankCleanArray = [swedbankDirty componentsSeparatedByString:@"</td>"];
    swedbankDirty = swedbankCleanArray[4];

    // Set result to value fetched from internet
    swedbankRate = [NSString stringWithFormat:@"%.2f", [swedbankDirty floatValue]];

}

And result is

2015-12-07 14:26:29.635 Photography[60338:18355297] 71.14
2015-12-07 14:26:29.684 Photography[60338:18355293] 71.14

I cant put my finger on it why does it get executed twice?

What the method is supposed to do is scan the HTML code of a webpage and get just one float number from the whole content for me to use later. Ye the code isnt perfect, still learning. Any ideas welcome.

Upvotes: 0

Views: 114

Answers (3)

gnasher729
gnasher729

Reputation: 52632

awakeFromNib is usually not a good place for that kind of thing. You should use awakeFromNib to do things that you would have wanted to do in Interface Builder, but for some reason couldn't - so just to fix problems that arise when you load a nib file.

For example, doing things in awakeFromNib gets you into trouble if you use the same class in a different context, and if you build a user interface in code instead of using a nib file, and your awakeFromNib doesn't get called at all anymore.

Upvotes: 1

Dmitri K.
Dmitri K.

Reputation: 197

You are both correct. Wow, what a silly mistake to make. Indeed another class was also calling awakeFromNib to do its stuff there too.

I put those calls in the viewDidLoad method and it is working as it needs now! Great! What a great way to learn this multithreading stuff! :)

Upvotes: 0

Andrea Lupattelli
Andrea Lupattelli

Reputation: 41

Check if awakeFromNib is called twice in your app... (see this question)

Upvotes: 0

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