Asynchronously set images in tableview

Question

I have a TableView using custom cells. I initially was setting grabbing an image from a URL in the cellForRowAtIndexPath method

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Answer 1

1. Create UIImageView Class File (i named it to MJTableImageView).

in MJTableImageView.h File

    @interface MJTableImageView : UIImageView< NSURLConnectionDelegate, NSURLConnectionDataDelegate >

    {
    NSMutableData *imageData ;
    long long expectedLength;
    NSURLConnection *currentConnection;
    NSString *File_name;

    }
    @property(nonatomic,readonly)UIActivityIndicatorView *loadingIndicator;
    @property(nonatomic)BOOL showLoadingIndicatorWhileLoading;

    -(void)setImageUrl:(NSURL *)imageUrl fileName:(NSString *)name;

    @end

in MJTableImageView.m File

-(void)setImageUrl:(NSURL *)imageUrl fileName:(NSString *)name
{
    // discard the previous connection
    if(currentConnection)
    {
        [currentConnection cancel];
    }

    File_name = name;

    //reset current image
    self.image = nil;


//    if(_showLoadingIndicatorWhileLoading)
//    {
        //show the loading indicator

        if(!_loadingIndicator)
        {
            CGFloat width = self.bounds.size.width*0.5;

            _loadingIndicator = [[UIActivityIndicatorView alloc] initWithFrame:CGRectMake((self.bounds.size.width-width)/2, (self.bounds.size.height-width)/2, 25.0 , 25.0)];
            _loadingIndicator.backgroundColor = [UIColor colorWithWhite:0.0 alpha:0.5];
            _loadingIndicator.layer.cornerRadius = width*0.1;
        }
        [self startLoadingIndicator];
//    }

    // initialize the placeholder data
    imageData = [NSMutableData data];


    // start the connection
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:imageUrl];
    request.cachePolicy = NSURLRequestUseProtocolCachePolicy;

    currentConnection = [NSURLConnection connectionWithRequest:request delegate:self];



}
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    //if the image view is reused in a table view for example to load another image  previous image is discarded
    if(connection != currentConnection)
    {
        [connection cancel];
        [self cleanUp];
        return;
    }

    // append new Data
    [imageData appendData:data];



    // show the partially loaded image
    self.image = [UIImage imageWithData:imageData];
}
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    expectedLength = response.expectedContentLength;
}
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    // clean up
    [self cleanUp];

}
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // show the full image
    self.image = [UIImage imageWithData:imageData];

    NSString *filename = [NSHomeDirectory() stringByAppendingFormat:@"/Documents/%@", File_name];
    NSData *data = UIImagePNGRepresentation([UIImage imageWithData:imageData]);
    [data writeToFile:filename atomically:YES];

    // clean up
    [self cleanUp];
}
-(void)cleanUp
{
    // clean up
    imageData = nil;
    [self stopLoadingIndicator];
}
-(void)startLoadingIndicator
{
    if(!_loadingIndicator.superview)
    {
        [self addSubview:_loadingIndicator];
    }
    [_loadingIndicator startAnimating];
}
-(void)stopLoadingIndicator
{
    if(_loadingIndicator.superview)
    {
        [_loadingIndicator removeFromSuperview];
    }
    [_loadingIndicator stopAnimating];
}

I am using StoryBoard so i add ImageClass(MJTableImageView) file to UItableviewcell ImageView and set tag number to it.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    NSDictionary *dict = [self.arr objectAtIndex:indexPath.row];

    UITableViewCell *cell = [self.MJTableView dequeueReusableCellWithIdentifier:@"MJImageCell"];
    if(cell == nil)
    {

    }
    UILabel *appName = (UILabel*)[cell.contentView viewWithTag:2];
    appName.text = [dict valueForKey:@"trackName"];

    MJTableImageView *imageview = (MJTableImageView *)[cell.contentView viewWithTag:1];

    NSString *url = [dict valueForKey:@"artworkUrl60"];

    NSString *filename = [NSHomeDirectory() stringByAppendingFormat:@"/Documents/%@",[dict valueForKey:@"trackName"] ];
    NSData *data = [NSData dataWithContentsOfFile:filename];
    if(data)
    {
        imageview.image = [UIImage imageWithData:data];
    }
    else
    {
        [imageview setImageUrl:[NSURL URLWithString:url] fileName:[dict valueForKey:@"trackName"]];
    }
    return  cell;
}

For More details see Github Project MJTableImageSwift it is in Swift.