NSRangeException randomly crash app

Question

1. My app crash ramdomly in _storeArray.
2. In viewDidLoad, have a method [self loadUrl] that parse a xml file then add an dictionary [_storeArray addObject:dictionary];
3. The crash happens when somehow the carousel reusingView call first then [self loadUrl].
4. I have added the if(_storeArray) but it still crash.

This is the exception:

2013-04-06 09:33:35.254 Semhora[7347:907] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array'

This is the code:

- (void)loadURL:(NSString *)newURL{

    // Create a success block to be called when the asyn request completes
    TBXMLSuccessBlock successBlock = ^(TBXML *tbxmlDocument) {


        [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
        // If TBXML found a root node, process element and iterate all children
        if (tbxmlDocument.rootXMLElement)
        {
            // Obtain root element
            TBXMLElement * root = tbxml.rootXMLElement;
            if (root)
            {
                [_storeArray removeAllObjects];
                TBXMLElement * elem_PLANT = [TBXML childElementNamed:@"principal" parentElement:root];
                while (elem_PLANT !=nil)
                {
                    TBXMLElement * elem_title = [TBXML childElementNamed:@"title" parentElement:elem_PLANT];
                    NSString *titleName = [TBXML textForElement:elem_title];

//                    TBXMLElement * elem_artist = [TBXML childElementNamed:@"text" parentElement:elem_PLANT];
//                    NSString *artistName = [TBXML textForElement:elem_artist];

                    TBXMLElement * elem_thumb = [TBXML childElementNamed:@"thumb_url" parentElement:elem_PLANT];
                    NSString *thumbName = [TBXML textForElement:elem_thumb];

                    TBXMLElement * elem_photo1 = [TBXML childElementNamed:@"photo1" parentElement:elem_PLANT];
                    NSString *photo1Name = [TBXML textForElement:elem_photo1];

                    TBXMLElement * elem_photo2 = [TBXML childElementNamed:@"photo2" parentElement:elem_PLANT];
                    NSString *photo2Name = [TBXML textForElement:elem_photo2];

                    TBXMLElement * elem_photo3 = [TBXML childElementNamed:@"photo3" parentElement:elem_PLANT];
                    NSString *photo3Name = [TBXML textForElement:elem_photo3];

                    TBXMLElement * elem_photo4 = [TBXML childElementNamed:@"photo4" parentElement:elem_PLANT];
                    NSString *photo4Name = [TBXML textForElement:elem_photo4];

                    TBXMLElement * elem_photo5 = [TBXML childElementNamed:@"photo5" parentElement:elem_PLANT];
                    NSString *photo5Name = [TBXML textForElement:elem_photo5];

                    NSDictionary *dictionary = [[NSDictionary alloc]initWithObjects:@[titleName, thumbName, photo1Name, photo2Name, photo3Name, photo4Name, photo5Name] forKeys:@[@"title", @"thumb_url", @"photo1", @"photo2", @"photo3", @"photo4", @"photo5",]];
                    elem_PLANT = [TBXML nextSiblingNamed:@"principal" searchFromElement:elem_PLANT];
                    [_storeArray addObject:dictionary];
                   [self startLoading:dictionary];
                     [[NSOperationQueue mainQueue] addOperationWithBlock:^{ [_carousel reloadData]; }];
                }


            }

        }

    };

    // Create a failure block that gets called if something goes wrong
    TBXMLFailureBlock failureBlock = ^(TBXML *tbxmlDocument, NSError * error) {
        NSLog(@"Error! %@ %@", [error localizedDescription], [error userInfo]);
    };

    // Initialize TBXML with the URL of an XML doc. TBXML asynchronously loads and parses the file.
    tbxml = [[TBXML alloc] initWithURL:[NSURL URLWithString:newURL]
                               success:successBlock
                               failure:failureBlock];

}

- (UIView *)carousel:(iCarousel *)carousel viewForItemAtIndex:(NSUInteger)index reusingView:(UIView *)view
{
    //create new view if no view is available for recycling
    if (view == nil)
    {
        FXImageView *imageView = [[FXImageView alloc] initWithFrame:CGRectMake(0, 0, 200.0f, 200.0f)];
        imageView.contentMode = UIViewContentModeScaleAspectFit;
        imageView.asynchronous = YES;
        imageView.reflectionScale = 0.5f;
        imageView.reflectionAlpha = 0.25f;
        imageView.reflectionGap = 10.0f;
        imageView.shadowOffset = CGSizeMake(0.0f, 2.0f);
        imageView.shadowBlur = 5.0f;
        imageView.cornerRadius = 10.0f;
        view = imageView;
    }

    //show placeholder
    ((FXImageView *)view).processedImage = [UIImage imageNamed:@"placeholder.png"];

    //set image

    NSLog(@"%@", _storeArray);
    if (_storeArray) {

        NSDictionary *tempdic = [_storeArray objectAtIndex:0];

        switch (index) {
            case 0:
                [(FXImageView *)view setImageWithContentsOfURL:[NSURL URLWithString:[tempdic objectForKey:@"photo1"]]];
                break;
            case 1:
                [(FXImageView *)view setImageWithContentsOfURL:[NSURL URLWithString:[tempdic objectForKey:@"photo2"]]];
                break;
            case 2:
                [(FXImageView *)view setImageWithContentsOfURL:[NSURL URLWithString:[tempdic objectForKey:@"photo3"]]];
                break;
            case 3:
               [(FXImageView *)view setImageWithContentsOfURL:[NSURL URLWithString:[tempdic objectForKey:@"photo4"]]];
                break;
            case 4:
                [(FXImageView *)view setImageWithContentsOfURL:[NSURL URLWithString:[tempdic objectForKey:@"photo5"]]];
                break;
            default:
                break;
        }
    }

    return view;
}

Answer 1

1. The current check for _storeArray only checks if the variable exists, but not if there are actually any elements in there. But after the check you simply assume that there is 1 element in the array without checking before if that is true.

   So change this

   if (_storeArray) {
   

   to this:

   if (_storeArray && [_storeArray count] > 0) {
   

2. In addition you are assuming that the dictionary will have a key for photo1 etc. But if not, the generated URL will be empty and as a consequence the view might also get a nil URL.

   I would change that as follows:

   NSDictionary *tempdic = [_storeArray objectAtIndex:0];
   NSString *tempObjKey = nil;
   
   switch (index) {
       case 0:
           tempObjKey = @"photo1";
           break;
       case 1:
           tempObjKey = @"photo2";
           break;
       case 2:
           tempObjKey = @"photo3";
           break;
       case 3:
           tempObjKey = @"photo4";
           break;
       case 4:
           tempObjKey = @"photo5";
           break;
       default:
           break;
   }
   
   if (tempObjKey && [tempdic objectForKey:tempObjKey])
       [(FXImageView *)view setImageWithContentsOfURL:[NSURL URLWithString:[tempdic objectForKey:tempObjKey]]];
   }
   

Answer 2

I need to know one thing, does your parsing happen before all this and successfully returns a array(NSLog it) because the array seems to be the problem here. You cannot directly take out the first object, you gotta stay defensive so do something like this.

 if (_storeArray) {

    if(_storeArray.count >0) {

    NSDictionary *tempdic = [_storeArray objectAtIndex:0];

    switch (index) { // all ur stmts }
    }}