Why doesn't NSOperationQueue execute a block submitted with addOperationWithBlock? - ios

Question

Here is the thing, I got some code, that does not execute (the compiler run the code but does not do anything)... Here is the code... Using NSURLSessionDelegate and [NSOperationQueue mainQueue] addOperationWithBlock
#interface tablaPosViewController : UIViewController <NSURLSessionDelegate>
#end
#implementation tablaPosViewController ()
- (void)viewDidLoad
{
//some code to set the view, labels and stuff
[self downloadTheHTMLdata] // this code download some data from WWW
}
- (void)downloadTheHMTLdata
{
//some code to set the session using an object
[object.downloadTask resume]; //Begins the download
}
- (void)toFixTablaPosiciones
{
//some code to do with the downloaded data from WWW (and HTML sheet)
//here, parse the HTML Sheet, and put some data into an Arrays, and another public vars
//call another method
[self PutTheDataInLabel];
}
- (void)PutTheDataInLabel
{
//some code to put all the data in every label
//take the public vars that was set in the previous method, and do some code with it
//and put the info into the labels
//call another method
[self MoreStuff];
}
- (void)MoreStuff
{
//some code..
}
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
//When the download finish this method fire up!
//this is to copy file from tmp folder to Docs folder
if ([fileManager fileExistsAtPath:[destinationURL path]])
{
[fileManager removeItemAtURL:destinationURL error:nil];
}
BOOL success = [fileManager copyItemAtURL:location //TMP download folder
toURL:destinationURL //Documents folder
error:&error];
//HERES COMES THE TROUBLE!!!
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
[self toFixTablaPosiciones]; //Call this method, that has other method calls!
}];
}
#end
UPDATE
This another code put methods in the queue...
-(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session{
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
[self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
if ([downloadTasks count] == 0) {
if (appDelegate.backgroundTransferCompletionHandler != nil) {
void(^completionHandler)() = appDelegate.backgroundTransferCompletionHandler;
appDelegate.backgroundTransferCompletionHandler = nil;
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
completionHandler();
}];
}
}
}];
}
The issue is when the download file ends, calls -(void)URLSession:(NSURLSession *)session downloadTask:... method and I wait to [[NSOperationQueue mainQueue] addOperationWithBlock:^{... runs everything... but it does not execute anythig of [self toFixTablaPosiciones]!!.
I ran the code step by step, and I see how the compiler runs all the code, method over method... but the view never updates, runs but not executes, simply does do anything, and I have an Activity Indicator, and want to stop it, but the lablels stills with de dummie data and the Activity Indicator never stops and never disappears.
In a previous view, I download another file using a similiar class, and downloads very quickly. Going to this view/class try to perform the download and this is the thing...
Hoping any body can help me and send me any advice. Thanks!

Answer 1

One technique I use, as do most experienced developers, is to use asserts and also NSLog (which you can comment on and off) to verify that assumptions you are making about your code are in fact true. Try cutting and pasting the below code and see what happens - it should help. In the future, don't bang your head on a wall - start adding asserts and logs. At some point you will find that some assumption is untrue.
-(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session {
NSLog(#"Received URLSessionDidFinishEventsForBackgroundURLSession: application state is %d", [UIApplication sharedApplication] applicationState];
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
[self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
NSLog(#"Download task count %d", [downloadTasks count]);
#warning "This looks like incorrect logic, but I don't know this background code. Wouldn't you see "1", or more? Won't you get an array of the tasks you submitted???
if ([downloadTasks count] == 0) {
assert(appDelegate.backgroundTransferCompletionHandler); // if this is nil, your app will be stuck in some odd state forever, so treat this like a fatal error
void(^completionHandler)() = appDelegate.backgroundTransferCompletionHandler;
appDelegate.backgroundTransferCompletionHandler = nil;
assert([NSOperationQueue mainQueue]); // why not?
assert(![NSOperationQueue mainQueue].isSuspended); // I looked at the class description, the queue **could** be suspended
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
NSLog(#"Completion Operation called!");
assert(completionHandler); // perhaps an ARC bug, unlikely, but then you cannot get this code to work, right?
completionHandler();
}];
}
}];
}