IOS Tableview takes 10 or more seconds to populate - ios

Question

I went from using an NSURLConnection in my tableview controller to using an NSURLSession in a separate class with a callback that is processed in the tableview controller.
Now the data returned from my website does not get displayed in the populated table for up to 20 seconds even though it was loaded long ago.
I have an 'add' button on the navigation bar of tableview which brings up another view. When I click the add button, I can see the data in my main tableview is already populated as it animates to the next view. Returning back to the main view and the data is there.
I have tried implementing a number of ways to reload the data but they have no effect.
The old way which works fine, only lets me have one connection. I needed to have several connections available to call based on options I might have selected which is the reason for creating a new class to handle the connections and placing its callback in the tableview.
But this has created the problem of not being able to view the parsed return data immediately.
To me, it seems to be some type of threading issue, but I don't know how to troubleshoot it or how to correct it, so I am hoping someone here can suggest something to try.
Here is the applicable code in my new class we will call NetWorkClass for purposes of illustration...
#pragma mark - Get Parents
+ (void)requestParentsWithCompletionHandler:(RequestCompletionHandler)completionBlock {
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:#"insert url here"]];
[request setHTTPMethod:#"POST"];
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfig];
[[session dataTaskWithRequest:request completionHandler:completionBlock] resume];
}
This typdef is in the header file for my new class NetworkClass...
typedef void (^RequestCompletionHandler)(NSData *data, NSURLResponse *response, NSError *error);
Then in the main thread of my tableview controller class I call a method that invokes the Network class to retrieve JSON data from a website.
The following snippet is called from ViewDidLoad in my tableview controller...
// Use NSSesssion to request JSON data from my website [self getParents];
NSLog(#"getParents has completed!");
// The view however, will not display for approximately 20 or 30 seconds unless I click on the Add button which instantiates another view // and then I see the data in the tableview right away as it animates to the new view. NSLog(#"parentsTable:%#",parentsTable);
NSLog outputs the following:
2014-02-11 16:10:27.385 myApp[12667:70b] parentsTable:; layer = ; contentOffset: {0, 0}>
The data has not yet been processed by the callback at this point, but the website has been sent the request and the repsonse is being returned.
The callback is implemented in getParents...
-(void)getParents
{
[NetWorkClass requestParentsWithCompletionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
if (!error) {
NSHTTPURLResponse *httpResp = (NSHTTPURLResponse*) response;
if (httpResp.statusCode == 200) {
if the response status code is 200, I propagate the data into the tableview and finish up by calling
[parentsTable reloadData];
All of the code following the statuscode check is identical to the code that works if I use an NSURLconnection (and its delegate methods) within the tableview to retrieve the data, so I have not included it here.
If I put a breakpoint at requestParentsWithCompletionHandler in getParents, and I single step from there, the first pass skips around my code. But if I then run from that point, it hits the breakpoint a second time and then falls thru to process the response, which is working as I would expect it since we have to wait a few milliseconds for the data to be obtained from the website.
The data has arrived within milliseconds, but it can take up to 20 seconds before the tableview fills in with data that was parsed if I do nothing.
Any help with this would be greatly appreciated.

Answer 1

You need to change your structure to the following:
In viewDidLoad You should call a method that will send an asynchronous request for the data. (strongly suggest using AFNetworking or restKit to do it instead of trying to get by with the code you are currently using)
On success you should populate an array with the data and [tableView reloadData]
You numberOfRowsInSection should look like the following:
If (!arrayContainingData) {
return 0; // For elegance, you can also return 1 and have a cell with an UIActivityMonitor
} else {
return arrayContainingData.count;
}
Finally use cellForRowAtIndexPath to build the cells.