Adding UIActivityIndicatorView on Synchronous Web Service data and Populating UITableView - ios

Question

I am fetching the data from a web service by synchronous method. I make the request to the web service then view freezes. I try to add the UIActivityIndicatorView before loading the data from the web service and stopped it after getting the data but activity indicator is not displayed.
I tried to put the web service data fetch operations on the different thread
[NSThread detachNewThreadSelector:#selector(fetchRequest) toTarget:self withObject:nil];
but at this time TableView crashes as it does not get the data for drawing the cells.
in fetchRequest function I am doing
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL
URLWithString:URLString]];
NSData *response = [NSURLConnection sendSynchronousRequest:request
returningResponse:nil error:nil];
NSError *jsonParsingError = nil;
NSDictionary *tableData = [NSJSONSerialization JSONObjectWithData:response
options:0
error:&jsonParsingError];
responseArray = [[NSMutableArray alloc]initWithArray:[tableData objectForKey:#"data"]];
for(int i = 0; i < responseArray.count; i++)
{
NSArray * tempArray = responseArray[i];
responseArray[i] = [tempArray mutableCopy];
}
This responseArray is used to fill the information in the cell
Please tell me how to do this. Any help will be appreciated ...

Answer 1

The problem lies in your very approach. Synchronous methods run on the main thread. And because the UI updates on the main thread, your app hangs.
So, the solution would be using an asynchronous method to download the data on a separate thread, so that your UI won't hang.
So, use the NSURLConnection's sendAsynchronousRequest. Here's some sample code :
NSURL *url = [NSURL URLWithString:#"YOUR_URL_HERE"];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
//this is called once the download or whatever completes. So you can choose to populate the TableView or stopping the IndicatorView from a method call to an asynchronous method to do so.
}];

Answer 2

You should better use Grand Central Dispatch to fetch the data like this so you dispatch it in a background queue and do not block the main thread which is also used for UI updates:
dispatch_queue_t myqueue = dispatch_queue_create("myqueue", NULL);
dispatch_async(myqueue, ^(void) {
[self fetchRequest];
dispatch_async(dispatch_get_main_queue(), ^{
// Update UI on main queue
[self.tableView reloadData];
});
});
Regarding the Activity indicator you can use in the start of the parsing:
[self.activityIndicator startAnimating];
self.activityIndicator.hidesWhenStopped = YES
And then when your table is filled with data:
[self.activityIndicator stopAnimating];