Loading images in background to optimize the loading in ios

Question

I am trying to optimize the load in my application, in fact, I have a lot of images that loaded in my application, and I spend a lot of time waiting for a view controller to ope

Answer 1

Yes, you can add placeholder image to it.

It will not slow down the scrolling and will load image accordingly with time.

Also import this file UIImageView+WebCache.m and MapKit Framework

Here is the link to download the files.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     static NSString *CellIdentifier = @"Cell";
        UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
        if (cell == nil) {
            cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
        }
    UIImageview*  iV = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 50, 50)];
   [iV setImageWithURL:[NSURL URLWithString:url] placeholderImage:[UIImage imageNamed:@"image_placeholder.gif"]];
   [cell.contentView addSubview:iV];
   [iV release];

}

Just clean, build and run.

Answer 2

Here is a slightly modified approach of Ramu Pasupoletis answer. I added the __block modifier to make the var img visible inside the block called on the main thread. Here is the complete method definition which I use in

-(UITableViewCell*)cellforRowAtIndexPath:(UIIndexPath*)indexPath;

for fetching the thumbnails lazily. I also added placeholders there for the cells UIImageViews.

//lazy loading of thumbnails for images in cell via bg thread
-(void)loadImageForCell:(CustomEditTableViewCell*)theCell withFilepath: (NSString*)filepath{

dispatch_queue_t q = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(q, ^{
    UIImage (__block *img) = [UIImage imageWithContentsOfFile:filepath];
    UIImage *thumbnail = [[GlobalFunctions sharedGlobalFunctions] imageOfSize:CGSizeMake(40, 40) fromImage:img];
    dispatch_async(dispatch_get_main_queue(), ^{
        theCell.imageView.image = thumbnail;
    });
});
}

Answer 3

You can use async imageview.

- (void) loadImageFromURL:(NSURL*)url placeholderImage:(UIImage*)placeholder cachingKey:(NSString*)key {
    self.imageURL = url;
    self.image = placeholder;

    NSData *cachedData = [FTWCache objectForKey:key];
    if (cachedData) {   
       self.imageURL   = nil;
       self.image      = [UIImage imageWithData:cachedData];
       return;
    }

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
    dispatch_async(queue, ^{
        NSData *data = [NSData dataWithContentsOfURL:url];

        UIImage *imageFromData = [UIImage imageWithData:data];

        [FTWCache setObject:data forKey:key];

        if (imageFromData) {
            if ([self.imageURL.absoluteString isEqualToString:url.absoluteString]) {
                dispatch_sync(dispatch_get_main_queue(), ^{
                    self.image = imageFromData;
                });
            } else {
//              NSLog(@"urls are not the same, bailing out!");
            }
        }
        self.imageURL = nil;
    });
}

Take a look at this link.You will have an idea on using async imageview.