How to create an array of UIImages

Question

I\'m storing an image from a Parse database like this:

PFFile *firstImageFile = self.product[@\"firstThumbnailFile\"];
[firstImageFile getDataInBackgroundWithBlo         


        

Answer 1

This is form of a common problem: how to do many asynch operations (without deeply nesting completion blocks) and know when they complete. The approach I use is to think of the parameters to the operations as a todo list, and build a method that handles the list recursively....

- (void)loadPFFiles:(NSArray *)array filling:(NSMutableDictonary *)results completion:(void (^)(BOOL))completion {
    NSInteger count = array.count;
    // degenerate case is an empty array which means we're done
    if (!count) return completion(YES);

    // otherwise, do the first operation on the to do list, then do the remainder
    PFFile *file = array[0];
    NSArray *remainder = [array subarrayWithRange:NSMakeRange(0, count-1)];

    [file getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error) {
        if (!error) {
            UIImage *image = [UIImage imageWithData:imageData];
            results[file.name] = image;
            [self loadPFFiles:remainder filling:results completion:completion];
        } else {
            completion(NO);
        }
    }];
}

Call it like this (guessing about your model a little bit):

NSArray *pfFiles = @[ self.product[@"firstThumbnailFile"], self.product[@"secondThumbnailFile"] ];
NSMutableDictionary *result = [@{} mutableCopy];

[self loadPFFiles:pfFiles filling:result completion:^(BOOL success) {
    if (success) {
        // result will be an dictionary of the loaded images
        // indexed by the file names
    }
}];