Question

I have added a gesture recognizer (two finger tap) that detects when the user presses on an image in UIWebView and brings up a UIActivityViewController to save the image and other stuff. My problem is that when I press on an image there is a lag (depending on how big the image size may be) and what im trying to achieve is that when the user double taps on the image i want to show an activity indicator until the image is ready to be saved and etc… I may add that i think the problem is here ‘imageToBeSaved = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];’ after i take out that code, there is no more lagging. Here’s my code:

// adding gesture recognizer to "website" (which is a "UIWebView")
UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(doubleTap:)];
doubleTap.numberOfTouchesRequired = 2;
[website addGestureRecognizer:doubleTap];

// actions on gesture detect and call actionsOnImage for options
-(void) doubleTap :(UITapGestureRecognizer*) sender {
[loadingImageActivityIndicator startAnimating];
int scrollPositionY = [[self.website stringByEvaluatingJavaScriptFromString:@"window.pageYOffset"] intValue];
int scrollPositionX = [[self.website stringByEvaluatingJavaScriptFromString:@"window.pageXOffset"] intValue];

int displayWidth = [[self.website stringByEvaluatingJavaScriptFromString:@"window.outerWidth"] intValue];
CGFloat scale = website.frame.size.width / displayWidth;

CGPoint pt = [sender locationInView:self.website];
pt.x *= scale;
pt.y *= scale;
pt.x += scrollPositionX;
pt.y += scrollPositionY;

NSString *js = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).tagName", pt.x, pt.y];
NSString *tagName = [self.website stringByEvaluatingJavaScriptFromString:js];

if ([tagName compare:@"IMG" options:NSCaseInsensitiveSearch]==NSOrderedSame) {
    NSLog(@"tagName was IMG");
    NSString *imgURL = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).src", pt.x, pt.y];
    NSString *urlToSave = [self.website stringByEvaluatingJavaScriptFromString:imgURL];
    NSURL *url = [NSURL URLWithString:urlToSave];
    imageToBeSaved = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];
    [website addSubview:loadingImageActivityIndicator];

    [self actionsOnImage];  // self made function with sharing capabilities (see below)
}

}

- (void) actionsOnImage {
[loadingImageActivityIndicator stopAnimating];

NSArray* dataToShare = [[NSArray alloc] initWithObjects:imageToBeSaved, nil];
UIActivityViewController* activityViewController =
[[UIActivityViewController alloc] initWithActivityItems:dataToShare
                                  applicationActivities:nil];
[self presentViewController:activityViewController animated:YES completion:^{}];
}

Answer 1

Perform loading of the image asynchronously. Rearrange your lines of code as follows

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),^{
     imageToBeSaved = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];
     [self actionsOnImage];
});

[website addSubview:loadingImageActivityIndicator];