Sending NSOperationQueue to UITableView as a DataSource - ios

Question

i have written code to downloading data from server using NSOperationQueue and NSOperation. and now i want to show progress on UserInterface. i used UITableView and used NSOpeartionQueue as a datasource in tableview delegate
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [[[Downloadmanager sharedInstance] downloadOperationQueue] count];
}
and bind NSOperation`s properties to UITableViewCell.
1) Is this a fisible solution to sending NSOperationQueue as a datasource to tableview delegate ?
2) How to implement notification to reload tableview when NSOperation's state changes?
Thanks.

Answer 1

I don't think it's the proper way of showing progress using NSOperationQueue as a datasource to tableview. You can use networking library like AFNetworking for downloading data and use setDownloadProgressBlock: method for showing progress. Refer this link for the code download progress.
It's easy to reload tableview when the download completes, just call [tableView reloadData] in completionblock.
Here is the code which shows image downloading using AFNetworking which you can easily change for data download.(refer this gist)
- (void)downloadMultiAFN {
// Basic Activity Indicator to indicate download
UIActivityIndicatorView *loading = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[loading startAnimating];
[self.imageView.superview addSubview:loading];
loading.center = self.imageView.center;
// Create a request from the url, make an AFImageRequestOperation initialized with that request
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:self.picUrl]];
AFImageRequestOperation *op = [[AFImageRequestOperation alloc] initWithRequest:request];
// Set a download progress block for the operation
[op setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {
if ([op.request.URL.absoluteString isEqualToString:#"http://www.pleiade.org/images/hubble-m45_large.jpg"]) {
self.progressBar.progress = (float) totalBytesRead/totalBytesExpectedToRead;
} else self.progressBar2.progress = (float) totalBytesRead/totalBytesExpectedToRead;
}];
// Set a completion block for the operation
[op setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
self.imageView.image = responseObject;
self.image = responseObject;
if ([op.request.URL.absoluteString isEqualToString:#"http://www.pleiade.org/images/hubble-m45_large.jpg"]) {
self.progressBar.progress = 0;
} else self.progressBar2.progress = 0;
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {}];
// Start the image download operation
[op start];
// Remove the activity indicator
[loading stopAnimating];
[loading removeFromSuperview];
}

Answer 2

That is an interesting idea, but I don't think it's a good practice make such a "high coupling" - linking model so tightly to the view.
I'd approach it as - download the data on the background thread as you already do - with NSOperationQueue but save it to some kind of an object; say NSMutableArray that serves as the data source for the table view.
Every time a single operation ends (use completion handlers or KVO to get informed) - update the table view. The update can be done two ways - reloading or updating. I'll leave the choice up to you - you can read further discussion about that in this question.