Question

I have a UITableViewwhich displays cells with images. On the cellForRowAtIndexPath method I launch a connection to fetch the image. I want to keep track of what images have been already requested in order to avoid requesting the same image multiple times.

I set up a method like this

+(void) setImageFromURL:(NSURL*) url fromImage:(UIImage*) srcImage to:(UIImageView*) dstImage wasRequested:(BOOL*) requested;

and call it like this

[Utils setImageFromURL:event.thumbURL fromImage:event.thumbImage to:cell.image wasRequested:event.thumbRequested];

where event.thumbRequested is a BOOL property. The method look like this

+(void) setImageFromURL:(NSURL*) url fromImage:(UIImage*) srcImage to:(UIImageView*) dstImage wasRequested:(BOOL*) requested{
    if (srcImage != nil) {
        dstImage.image = srcImage;
    } else if (!requested) {
        requested = YES;
        @try {
            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                NSData * data = [[NSData alloc] initWithContentsOfURL: url];
                if ( data == nil )
                    return;
                dispatch_async(dispatch_get_main_queue(), ^{
                    __block UIImage* srcImage = [UIImage imageWithData: data];
                    dstImage.image = srcImage;
                });
                [data release];
            });
        }
        @catch (NSException *exception) {
            NSLog(exception.debugDescription);
        }
    }
}

My problem is the BOOL is not changing due to the pass by value behavior in Objective-C. Can anyone recommend a way for being able to update the BOOL in the event object from inside the mehod?

Answer 1

The line:

requested = YES;

needs to be:

if (requested) {
    *requested = YES;
}

The check is just incase nil was passed in for requested.

Edit: And the call should be:

BOOL requested = event.thumbRequested;
[Utils setImageFromURL:event.thumbURL fromImage:event.thumbImage to:cell.image wasRequested:&requested];
event.thumbRequested = requested;