I have 3 blocks of code that must execute one by one after previous finished. My implementation not works. I need some help to do it. My code bellow.
for (NSString *i in items)
{
[[RequestAPI sharedInstance]downloadImage:i completion:^(AFHTTPRequestOperation *operation, UIImage *image, NSError *error) {
//here main thread I receive images and go to BG
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
// here I save image on disk and get path
NSString *path = [ImageManager saveImageToDisk:image toEntity:entity withparams:#{#"save" : #"lala"}];
__block NSMutableDictionary *attachments = [NSMutableDictionary dictionary];
__block NSMutableArray *photoPaths = [NSMutableArray array];
dispatch_async(dispatch_get_main_queue(), ^{
//block1. here I load entity and dictionary from it with NSKeyedUnarchiver from CD and set to it image path
if (entity.attachments)
{
attachments = [NSKeyedUnarchiver unarchiveObjectWithData:entity.attachments];
if (attachments[type])
{
photoPaths = attachments[type];
}
}
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
//block2. here I check all images equality ti themselves in entity
BOOL haveDublicate = NO;
NSData *i = [ImageManager imageDataFromPath:path];
NSArray *photoImages = [ImageManager imageDatasFromPaths:photoPaths];
for (NSData *saved in photoImages)
{
if ([saved isEqualToData: i])
{
haveDublicate = YES;
}
}
if (!photoPaths)
{
photoPaths = [NSMutableArray array];
}
dispatch_async(dispatch_get_main_queue(), ^{
//block3. and finally if all ok I save image path, change load counter and post notification
if (path.length
&& ![photoPaths containsObject:path]
&& !haveDublicate
)
{
[photoPaths addObject:path];
[savedLinks setObject:photoPaths forKey:type];
entity.attachments = [NSKeyedArchiver archivedDataWithRootObject:savedLinks];
[self saveContext];
}
[RequestAPI sharedInstance].downloadsCount -= 1;
[[NSNotificationCenter defaultCenter]postNotificationName:kReloadFeedData object:nil];
});
});
});
});
}];
As dispatch_async says they will be executed asynchronous and not synchronous as you expected. Use dispatch_sync instead.
If you want to execute your code on a separate thread simple do the following
// create your thread
dispatch_queue_t queue = dispatch_queue_create("My Other Queue", 0);
// execute your synchronous block on the thread you've just created
dispatch_sync(queue,^{
// add your implementation here to be executed on your separate thread
dispatch_sync(dispatch_get_main_queue()^{
// update your UI here. Don't forget you can only update UI on the main thread
});
});
Related
I follow RAY WENDERLICH GCD tutorial- part 2, and I don't get this:
First implementation
- (void)downloadPhotosWithCompletionBlock:(BatchPhotoDownloadingCompletionBlock)completionBlock
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ // 1
__block NSError *error;
dispatch_group_t downloadGroup = dispatch_group_create(); // 2
for (NSInteger i = 0; i < 3; i++) {
NSURL *url;
switch (i) {
case 0:
url = [NSURL URLWithString:kOverlyAttachedGirlfriendURLString];
break;
case 1:
url = [NSURL URLWithString:kSuccessKidURLString];
break;
case 2:
url = [NSURL URLWithString:kLotsOfFacesURLString];
break;
default:
break;
}
dispatch_group_enter(downloadGroup); // 3
Photo *photo = [[Photo alloc] initwithURL:url
withCompletionBlock:^(UIImage *image, NSError *_error) {
if (_error) {
error = _error;
}
dispatch_group_leave(downloadGroup); // 4
}];
[[PhotoManager sharedManager] addPhoto:photo];
}
dispatch_group_wait(downloadGroup, DISPATCH_TIME_FOREVER); // 5
dispatch_async(dispatch_get_main_queue(), ^{ // 6
if (completionBlock) { // 7
completionBlock(error);
}
});
});
}
Second Implementation:
- (void)downloadPhotosWithCompletionBlock:(BatchPhotoDownloadingCompletionBlock)completionBlock
{
// 1
__block NSError *error;
dispatch_group_t downloadGroup = dispatch_group_create();
for (NSInteger i = 0; i < 3; i++) {
NSURL *url;
switch (i) {
case 0:
url = [NSURL URLWithString:kOverlyAttachedGirlfriendURLString];
break;
case 1:
url = [NSURL URLWithString:kSuccessKidURLString];
break;
case 2:
url = [NSURL URLWithString:kLotsOfFacesURLString];
break;
default:
break;
}
dispatch_group_enter(downloadGroup); // 2
Photo *photo = [[Photo alloc] initwithURL:url
withCompletionBlock:^(UIImage *image, NSError *_error) {
if (_error) {
error = _error;
}
dispatch_group_leave(downloadGroup); // 3
}];
[[PhotoManager sharedManager] addPhoto:photo];
}
dispatch_group_notify(downloadGroup, dispatch_get_main_queue(), ^{ // 4
if (completionBlock) {
completionBlock(error);
}
});
}
I the first implementation the relevant code is surrounded with dispatch_async and everything is super clear.
BUT, the second implementation is unclear! I don't get it, how the GCD mechanism is taking any part beside of the notification for enter and leave?
The first implementation runs a background thread starting at
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ // 1
So the whole function runs there. But this background thread gets eventually blocked at this line (it waits for all the photos to be downloaded):
dispatch_group_wait(downloadGroup, DISPATCH_TIME_FOREVER);
This is all fine since you are not blocking the main thread. But it is a bit of a clumsy implementation since,
you block a thread where you really have not to and
the code looks a bit ugly with the dispatch_async around the whole function.
So the second implementation has two benefits:
It's not that "ugly" and a bit more readable (because you get rid of the dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{})
and there is no block, because dispatch_group_notify serves as the asynchronous completion block.
The first method is an asynchronous method. You can call it from any thread, including the main thread. It will perform actions in a background thread, and when it's done, it will dispatch the callback block on the main thread. A call to this method returns immediately, the callback will be called a lot later.
The second method is a blocking method. The method will not finish until the photos are downloaded, and then it calls your callback method. This method should most definitely not be called from the main thread, only from a background thread.
I am new to blocks and am trying to figure out how to wait for the block to finish before performing my action (in this case a nslog) So how can I wait till the block is done before performing this nslog in the code below: NSLog(#"convertedPhotos::%#",convertedImages);
convertedImages = [[NSMutableArray alloc] init];
for (NSDictionary *photo in photos) {
// photo is a dictionary containing a "caption" and a "urlRep"
[photoUrls addObject:photo[#"urlRep"]];
}
if (photoUrls.count) {
for (id photos in photoUrls){
NSString *urlString = photos;
[self base64ImageAtUrlString:urlString result:^(NSString *base64) {
[jsonWithPhotos setObject:convertedImages forKey:#"photo64"];
NSError *error;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:jsonWithPhotos
options:NSJSONWritingPrettyPrinted // Pass 0 if you don't care about the readability of the generated string
error:&error];
if (! jsonData) {
NSLog(#"Got an error: %#", error);
} else {
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
NSLog(#"json::%#",jsonString);
}
}];
}
}
else {
NSLog(#"where are my urls?");
}
NSLog(#"convertedPhotos::%#",convertedImages);
}
}
this method/block is called from above
- (void)base64ImageAtUrlString:(NSString *)urlString result:(void (^)(NSString *))completion {
NSURL *url = [NSURL URLWithString:urlString];
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library assetForURL:url resultBlock:^(ALAsset *asset) {
// borrowing your code, here... didn't check it....
ALAssetRepresentation *representation = [asset defaultRepresentation];
CGImageRef imageRef = [representation fullResolutionImage];
//TODO: Deal with JPG or PNG
NSData *imageData = UIImageJPEGRepresentation([UIImage imageWithCGImage:imageRef], 0.1);
NSString *base64 = [imageData base64EncodedString];
completion(base64);
[convertedImages addObject:base64];
// NSLog(#"converted::%#",convertedImages);
} failureBlock:^(NSError *error) {
NSLog(#"that didn't work %#", error);
}];
}
I would use NSOperationQueue (or dispatch queue) and NSCondition (or dispatch group) to wait for operations to complete. It is also important to wrap blocks in #autoreleasepool to flush memory once you do not need it if you work with memory consuming objects like NSData.
example:
// create results array
__block NSMutableArray* results = [NSMutableArray new];
// create serial queue
dispatch_queue_t queue = dispatch_queue_create("myQueue", 0);
for(NSInteger i = 0; i < 10; i++) {
// enqueue operation in queue
dispatch_async(queue, ^{
// create semaphore
dispatch_semaphore_t sema = dispatch_semaphore_create(0);
// do something async, I do use another dispatch_queue for example
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
// wrap in autoreleasepool to release memory upon completion
// in your case wrap the resultBlock in autoreleasepool
#autoreleasepool {
// here for example the nested operation sleeps for two seconds
sleep(2);
// add the operation result to array
// I construct an array of strings for example
[results addObject:[NSString stringWithFormat:#"Operation %d has finished.", i]];
// signal that nested async operation completed
// to wake up dispatch_semaphore_wait below
dispatch_semaphore_signal(sema);
}
});
// wait until the nested async operation signals that its finished
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
NSLog(#"Finished single operation.");
});
}
// will be called once all operations complete
dispatch_async(queue, ^{
NSLog(#"Finished all jobs.");
NSLog(#"Results: %#", results);
});
For any non-main queue use semaphores
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// some serious stuff here
...
dispatch_semaphore_signal(semaphore);
});
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
In case you want to wait for async task execution being in the main queue - you wouldn't probably want to block it while waiting for a semaphore.
I use this construction which doesn't freeze the UI for the main queue only.
__block BOOL flag = NO;
dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// some serious stuff here
...
flag = YES;
});
// Run until 'flag' is not flagged (wait for the completion block to finish executing
while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, true) && !flag){};
Your best option is not to use blocks directly. Instead, create instances of NSBlockOperation and add them to an operation queue. Then create one more NSBlockOperation and make it dependent upon all of the other operations. This ensures that the last operation is only run after all others are completed and allows you to control how many operations will run at any one time.
If you have nested block calls, or some API that you can't change to enable this then you can still do it if you create an NSOperation subclass such that the operation does not complete until all of the asynchronous operations are complete. Take a look at dribin.org concurrent operations.
I have a UITableView that gets its data from an array. Populating that array, however, requires downloading and parsing large chucks of data from the Web. That being the case, I'd like perform those operations in a background thread. Here's what I've got so far:
#interface MyClass()
#property (nonatomic, strong) NSArray *model;
#end
#implementation MyClass
- (void) getData {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:SOME_URL]];
if (data) {
NSMutableArray *arr = [NSMutableArray array];
//Populate arr with data just fetched, which can take a while
dispatch_async(dispatch_get_main_queue(), ^{
//THIS IS THE STEP I AM UNSURE ABOUT. SHOULD I DO:
self.model = arr;
//OR
self.model = [NSArray arrayWithArray:arr];
//OR
self.model = [arr copy];
//OR
//something else?
});
}
});
}
#end
Thank you!
// you can use any string instead "mythread"
dispatch_queue_t backgroundQueue = dispatch_queue_create("com.mycompany.myqueue", 0);
dispatch_async(backgroundQueue, ^{
// Send Request to server for Data
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:SOME_URL]];
dispatch_async(dispatch_get_main_queue(), ^{
// Receive Result here for your request and perform UI Updation Task Here
if ([data length] > 0) {
// if you receive any data in Response, Parse it either (XML or JSON) and reload tableview new data
}
});
});
You should do:
self.model = arr;
The reference to self calls the setter, which will release any previous references in that variable and then add a reference count to arr so it doesn't go out of scope. If you were accessing the ivar directly you would do:
[model release];
model = [arr retain];
Take a look at this link Understanding dispatch_async and this https://developer.apple.com/library/ios/documentation/General/Conceptual/ConcurrencyProgrammingGuide/OperationQueues/OperationQueues.html
You should add DISPATCH_QUEUE_PRIORITY_BACKGROUND instead of DISPATCH_QUEUE_PRIORITY_DEFAULT to run this on the background.
By using DISPATCH_QUEUE_PRIORITY_DEFAULT you just made your task be classified as a normal task. If you have changed it to higher or lower priority, the queue would have run it before or after some other tasks, respectively.
I have a method in which I run a couple of other methods. These have completion blocks, I only want to return a value at the end of my main method once I have a result from each of my sub methods. Example:
-(NSMutableDictionary *)mainMethod
{
[self subMethod1Complete:^(NSMutableArray *results)
{
}
[self subMethod2Complete:^(NSMutableArray *results)
{
}
//return...
}
I only want to return my dictionary at the end once the two sub method have completed. How can I do this?
I did have the idea of storing a BOOL for each method, so I know, NO incomplete and YES complete. So when both are YES, I return my dict. But how I can call it on time and not prematurely?
Update
I have tweaked my code to use a completion block, so when I finally receive the data from two other completion blocks from other methods, I run the final one with compiled results. Below you can see my method. You can see my method below, no success thus far, the final completion block is still getting called prematurely.
Important bits for me. getTitles and getThumbnails methods. In the completion block of these I get the data I need. Only when I have both of these, do I want to call my final completion block of this main method. As a result, it will pass on both titles and thumbnails once they have been received.
-(void)getFeedForUserID:(NSString *)channelID delegate:(id<YTHelperDelegate>)delegate complete:(void (^)(NSMutableDictionary * result))completionBlock properties:(NSString *)element, ...
{
va_list args;
va_start(args, element);
NSMutableArray *array = [NSMutableArray new];
for (NSString *arg = element; arg != nil; arg = va_arg(args, NSString *)) [array addObject:arg];
va_end(args);
NSMutableDictionary *resultsDict = [NSMutableDictionary new];
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_group_t group = dispatch_group_create();
for (NSString *string in array)
{
if ([string isEqualToString:kFeedElementTitle])
{
dispatch_group_async(group, queue, ^{
[self getTitlesArrayForChannel:channelID completionHandler:^(NSMutableArray *results) {
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:results forKey:kFeedElementTitle];
});
}];
});
}
if ([string isEqualToString:kFeedElementTitle])
{
dispatch_group_async(group, queue, ^{
[self getThumbnailsArrayForChannel:channelID completionHandler:^(NSMutableArray *results) {
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:results forKey:kFeedElementThumbnail];
});
}];
});
}
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
completionBlock(resultsDict);
});
}
You can use GCD and the dispatch groups feature. Here's an article that explains it: http://www.objc.io/issue-2/low-level-concurrency-apis.html#groups
For example in your case, your code might look something like this (shamelessly copied from the article and adapted a bit)...
- (void)asyncMethod {
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_group_async(group, queue, ^(){
NSMutableArray * results = [self subMethod1];
dispatch_group_async(group, dispatch_get_main_queue(), ^(){
self.subMethod1Results = results;
});
});
dispatch_group_async(group, queue, ^(){
NSMutableArray * results = [self subMethod2];
dispatch_group_async(group, dispatch_get_main_queue(), ^(){
self.subMethod2Results = results;
});
});
// This block will run once everything above is done:
dispatch_group_notify(group, dispatch_get_main_queue(), ^(){
// notify the app that both sets of data are ready
[self notifyWorkIsDone];
// and release the dispatch group
dispatch_release(group);
});
}
This requires a little modification to how your class works, because the above method is asynchronous (which is a good thing--it's not going to block your app while all that work is being done). All you need is some sort of handler to call and notify your app that your data is ready and you can update your UI or do whatever additional processing is necessary.
You are looking for GCD's dispatch_group APIs. Here is some sample code from Apple's Concurrency Programming Guide:
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
// Add a task to the group
dispatch_group_async(group, queue, ^{
// Some asynchronous work
});
// Do some other work while the tasks execute.
// When you cannot make any more forward progress,
// wait on the group to block the current thread.
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
// Release the group when it is no longer needed.
dispatch_release(group);
Comments on updated code:
Are you sure your mistake is not that your second if statement checks kFeedElementTitle a second time instead of kFeedElementThumbnail which I think may be what you intended?
Updated with working example:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
NSString *kFeedElementTitle = #"some";
NSString *kFeedElementThumbnail = #"strings";
NSArray *array = #[#"some", #"test", #"strings"];
NSMutableDictionary *resultsDict = [NSMutableDictionary new];
NSLog(#"App launched");
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
for (NSString *string in array)
{
if ([string isEqualToString:kFeedElementTitle])
{
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:5]; // simulate network call
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:#"title result" forKey:kFeedElementTitle];
NSLog(#"Received title result");
});
});
}
if ([string isEqualToString:kFeedElementThumbnail]) // Note: this was changed to kFeedElementThumbnail from kFeedElementTitle
{
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:10]; // simulate network call
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:#"thumbnail result" forKey:kFeedElementThumbnail];
NSLog(#"Received thumbnail result");
});
});
}
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(#"final dictionary: %#", resultsDict);
});
return YES;
}
Output:
2013-07-16 21:02:46.468 d[947:a0b] App launched
2013-07-16 21:02:51.471 d[947:a0b] Received title result
2013-07-16 21:02:56.471 d[947:a0b] Received thumbnail result
2013-07-16 21:02:56.472 d[947:a0b] final dictionary: {
some = "title result";
strings = "thumbnail result";
}
you do not know when the blocks are going to return so you will not know if you have the data at the time, if i may make a suggestion you call a method with in those blocks that method will check to see if both dictionaries are set and if they are then continue with the process otherwise don't continue
- (void)mainMethod
{
[self subMethod1Complete:^(NSMutableArray *results)
{
self.result1 = results;
[self method3];
}
[self subMethod2Complete:^(NSMutableArray *results)
{
self.results2 = results;
[self method3];
}
}
- (void)method3 {
if ( self.results1 != nil && self.results2 != nil ) {
[self startProcedure];
} else {
// do nothing
}
}
although all together i would suggest reworking your code to do this differently, simply because you can't guarantee that one of the blocks will be done by the time of the return, let alone both of them
you can also do something like this
-(NSMutableDictionary *)mainMethod
{
[self subMethod1Complete:^(NSMutableArray *results)
{
}
[self subMethod2Complete:^(NSMutableArray *results)
{
}
while(result == nil)
sleep(1);
//return...
}
which again is really bad.... it's just better to re-write the code
I am downloading four plist files asynchronously over the internet. I need to wait until all four files are downloaded, until I either on the first run, push a UIViewController, or on all subsequent runs, refresh the data, and reload all my UITableViews.
On the first run, everything works perfectly. When refreshing though, all four url requests are called, and started, but never call their completion or failure blocks, and the UI freezes. Which is odd since I preform all operations in a background thread. I have not been able to figure out why this is happening.
The first load and the refresh methods call the four "update" methods in the same way, and use NSCondition in the same way.
For the first run:
- (void)loadContentForProgram:(NSString *)programPath
{
NSLog(#"Start Load Program");
AppDelegate *myDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
hud = [[MBProgressHUD alloc] initWithView:myDelegate.window];
[myDelegate.window addSubview:hud];
hud.labelText = #"Loading...";
hud.detailsLabelText = #"Loading Data";
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
//Do stuff here to load data from files
//Update From online files
hud.detailsLabelText = #"Updating Live Data";
resultLock = NO;
progressLock = NO;
recallLock = NO;
stageLock = NO;
condition = [[NSCondition alloc] init];
[condition lock];
[self updateCurrentCompsText];
[self updateCompetitionResults];
[self updateCompetitionRecalls];
[self updateCompetitionProgress];
while (!resultLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!stageLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!recallLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!progressLock) {
[condition wait];
}
NSLog(#"Unlock");
[condition unlock];
updateInProgress = NO;
//Reset Refresh controls and table views
self.refreshControlsArray = [[NSMutableArray alloc] init];
self.tableViewsArray = [[NSMutableArray alloc] init];
NSLog(#"Finished Loading Program");
[[NSNotificationCenter defaultCenter] postNotificationName:#"WMSOFinishedLoadingProgramData" object:nil]; //Pushes view controller
dispatch_async(dispatch_get_main_queue(), ^{
[MBProgressHUD hideHUDForView:myDelegate.window animated:YES];
});
});
}
When refreshing data:
- (void)updateProgramContent
{
if (!updateInProgress) {
updateInProgress = YES;
for (int i = 0; i < self.refreshControlsArray.count; i++) {
if (!((UIRefreshControl *)self.refreshControlsArray[i]).refreshing) {
[self.refreshControlsArray[i] beginRefreshing];
[self.tableViewsArray[i] setContentOffset:CGPointMake(0.0, 0.0) animated:YES];
}
}
resultLock = NO;
stageLock = NO;
recallLock = NO;
progressLock = NO;
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
condition = [[NSCondition alloc] init];
[condition lock];
[self updateCompetitionProgress];
[self updateCompetitionRecalls];
[self updateCompetitionResults];
[self updateCurrentCompsText];
while (!resultLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!stageLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!recallLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!progressLock) {
[condition wait];
}
NSLog(#"Unlock");
[condition unlock];
});
for (int i = 0; i < self.refreshControlsArray.count; i++) {
[self.refreshControlsArray[i] performSelector:#selector(endRefreshing) withObject:nil afterDelay:1.0];
[self.tableViewsArray[i] performSelector:#selector(reloadData) withObject:nil afterDelay:1.0];
}
updateInProgress = NO;
}
}
The block below that appears in each loading method above, corresponds to a method that will download and update a specific piece of data.
[self updateCompetitionProgress];
[self updateCompetitionRecalls];
[self updateCompetitionResults];
[self updateCurrentCompsText];
which runs:
- (void)updateCompetitionResults
{
__block NSDictionary *competitionResultsData = nil;
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:#"Some URL",[self.programName stringByReplacingOccurrencesOfString:#" " withString:#"%20"]]] cachePolicy:NSURLCacheStorageNotAllowed timeoutInterval:20.0];
AFPropertyListRequestOperation *operation = [AFPropertyListRequestOperation propertyListRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id propertyList) {
competitionResultsData = (NSDictionary *)propertyList;
[competitionResultsData writeToFile:[#"SOME LOCAL PATH"] atomically:NO];
[self updateCompetitionResultsWithDictionary:competitionResultsData];
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id propertyList) {
competitionResultsData = [NSDictionary dictionaryWithContentsOfFile:[#"SOME LOCAL PATH"]];
NSLog(#"Failed to retreive competition results: %#", error);
[self updateCompetitionResultsWithDictionary:competitionResultsData];
}];
[operation start];
}
and the completion and failure blocks call the same method to update the data
- (void)updateCompetitionResultsWithDictionary:(NSDictionary *)competitionResultsData
{
//Do Stuff with the data here
resultLock = YES;
[condition signal];
}
So, Why does this work on the first run, but not any of the subsequent runs?
As I mentioned in my comments, above, the most obvious problem is that you're invoking methods that use condition before you initialize condition. Make sure initialize condition before you start calling updateCompetitionResults, etc.
In terms of a more radical change, I might suggest retiring NSCondition altogether, and use operation queues:
I might use NSOperationQueue (or you can use dispatch groups, too, if you want, but I like the operation queue's ability to configure how many concurrent operations you can operate ... also if you get to a point that you want to cancel operations, I think NSOperationQueue offers some nice features there, too). You can then define each download and processing as a separate NSOperation (each of the downloads should happen synchronously, because they're running in an operation queue, you get the benefits of asynchronous operations, but you can kick off the post-processing immediately after the download is done). You then just queue them up to run asynchronously, but define a final operation which is dependent upon the other four will kick off as soon as the four downloads are done. (By the way, I use NSBlockOperation which provides block-functionality for NSOperation objects, but you can do it any way you want.)
And whereas your updateProgramContent might download asynchronously, it processes the four downloaded files sequentially, one after another. Thus, if the first download takes a while to download, it will hold up the post-processing of the others. Instead, I like to encapsulate both the downloading and the post processing of each of the four plist files in a single NSOperation, each. Thus, we enjoy maximal concurrency of not only the downloading, but the post-processing, too.
Rather than using the AFNetworking (which I'm generally a big fan of) plist-related method, I might be inclined to use NSDictionary and NSArray features that allow you to download a plist from the web and load them into the appropriate structure. These dictionaryWithContentsOfURL and arrayWithContentsOfURL run synchronously, but because we're doing this in a background operation, everything runs asynchronously like you want. This also bypasses the saving them to files. If you wanted them saved to files in your Documents directory, you can do that easily, too. Clearly, if you're doing something sophisticated in your downloading of the plist files (e.g. your server is engaging in some challenge-response authentication), you can't use the convenient NSDictionary and NSArray methods. But if you don't need all of that, the simple NSDictionary and NSArray methods, ___WithContentsOfURL make life pretty simple.
Pulling this all together, it might look like:
#interface ViewController ()
#property (nonatomic, strong) NSArray *competitions;
#property (nonatomic, strong) NSDictionary *competitionResults;
#property (nonatomic, strong) NSDictionary *competitionRecalls;
#property (nonatomic, strong) NSDictionary *competitionProgress;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self transfer];
}
- (void)allTransfersComplete
{
BOOL success;
if (self.competitions == nil)
{
success = FALSE;
NSLog(#"Unable to download competitions");
}
if (self.competitionResults == nil)
{
success = FALSE;
NSLog(#"Unable to download results");
}
if (self.competitionRecalls == nil)
{
success = FALSE;
NSLog(#"Unable to download recalls");
}
if (self.competitionProgress == nil)
{
success = FALSE;
NSLog(#"Unable to download progress");
}
if (success)
{
NSLog(#"all done successfully");
}
else
{
NSLog(#"one or more failed");
}
}
- (void)transfer
{
NSURL *baseUrl = [NSURL URLWithString:#"http://insert.your.base.url.here/competitions"];
NSURL *competitionsUrl = [baseUrl URLByAppendingPathComponent:#"competitions.plist"];
NSURL *competitionResultsUrl = [baseUrl URLByAppendingPathComponent:#"competitionresults.plist"];
NSURL *competitionRecallsUrl = [baseUrl URLByAppendingPathComponent:#"competitionrecalls.plist"];
NSURL *competitionProgressUrl = [baseUrl URLByAppendingPathComponent:#"competitionprogress.plist"];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 4; // if your server doesn't like four concurrent requests, you can ratchet this back to whatever you want
// create operation that will be called when we're all done
NSBlockOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
// any stuff that can be done in background should be done here
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// any user interface stuff should be done here; I've just put this in a separate method so this method doesn't get too unwieldy
[self allTransfersComplete];
}];
}];
// a variable that we'll use as we create our four download/process operations
NSBlockOperation *operation;
// create competitions operation
operation = [NSBlockOperation blockOperationWithBlock:^{
// download the competitions and load it into the ivar
//
// note, if you *really* want to download this to a file, you can
// do that when the download is done
self.competitions = [NSArray arrayWithContentsOfURL:competitionsUrl];
// if you wanted to do any post-processing of the download
// you could do it here.
NSLog(#"competitions = %#", self.competitions);
}];
[completionOperation addDependency:operation];
// create results operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionResults = [NSDictionary dictionaryWithContentsOfURL:competitionResultsUrl];
NSLog(#"competitionResults = %#", self.competitionResults);
}];
[completionOperation addDependency:operation];
// create recalls operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionRecalls = [NSDictionary dictionaryWithContentsOfURL:competitionRecallsUrl];
NSLog(#"competitionRecalls = %#", self.competitionRecalls);
}];
[completionOperation addDependency:operation];
// create progress operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionProgress = [NSDictionary dictionaryWithContentsOfURL:competitionProgressUrl];
NSLog(#"competitionProgress = %#", self.competitionProgress);
}];
[completionOperation addDependency:operation];
// queue the completion operation (which is dependent upon the other four)
[queue addOperation:completionOperation];
// now queue the four download and processing operations
[queue addOperations:completionOperation.dependencies waitUntilFinished:NO];
}
#end
Now, I don't know which of your plist's are arrays and which are dictionaries (in my example, I made competitions an array and the rest were dictionaries keyed by the competition id), but hopefully you get the idea of what I was shooting for. Maximize concurrency, eliminate NSCondition logic, really make the most of NSOperationQueue, etc.
This may be all to much to take in, but I only mention it as an alternative to NSCondition. If your current technique works, that's great. But the above outlines how I would tackle a challenge like this.