Initializing new UIDocument with some data - ios

I've been reading everything I can here about UIDocument and UIManagedDocument since there is more help on UIManagedDocument and it's a subclass of UIDocument, but I've not been able to figure what I need to do about this.
When the user hits the add button for my app to create a new document I need to create the document and have a couple of items prepopulated into it. My code for doing this works fine as long as I am single-stepping through the debugger, but at full speed the couple of items don't make it into the document.
I store a reference to the document in my AppDelegate and have a macro defined for simplified reading in the code:
#define SelectedDocument [(AppDelegate *)[[UIApplication sharedApplication] delegate] selectedDocument]
So in handling the add request, my code does this:
GnKDocument *tmp = [[GnKDocument alloc] initWithFileURL:fileURL];
[(AppDelegate *)[[UIApplication sharedApplication] delegate] setSelectedDocument:tmp];
[SelectedDocument saveToURL:fileURL forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
if (success) {
[SelectedDocument openWithCompletionHandler:^(BOOL success) {
if (success) {
[SelectedDocument setDateCreated:[NSDate date]];
NSString *c1UUID = [SelectedDocument appendChapterWithName:#"Chapter 1"
withColor:kChapterColorYellow];
NSString *p1c1UUID = [SelectedDocument appendPageWithParent:c1UUID
withName:#"Page 1"
withColor:kPageColorRed];
NSLog(#"Just added Page 1 as %# to chapter %#", p1c1UUID, c1UUID);
[SelectedDocument closeWithCompletionHandler:^(BOOL success) {
}];
}
}
}];
The two append calls into my UIDocument subclass do their work and then call
[self updateChangeCount:UIDocumentChangeDone];
And as a testing step I overrode that method just to log out that changes were being made:
- (void)updateChangeCount:(UIDocumentChangeKind)change
{
[super updateChangeCount:change];
NSLog(#"GnKDocument recording a change");
}
Am I doing things in the right order? Should I be dispatching calls off to various queues?
Init the instance
Save it for creating
Open it (to add my initial items to it)
Make my additions
Close it (according to the docs, closeWithCompletionHandler: asynchronously saves any changes).
Again, if I set breakpoints at each call (saveToURL:, openWithCompletionHandler:, and closeWithCompletionHandler) and "step over" those calls, then run to get into the completion handlers, the document ends up on disk as I intended. If I disable my breakpoints and run again, the document is created on disk and the changes are logged, but the closed file does not contain my two initial elements.

For the longest time I thought the difference was the speed with which the code was executing was either creating or avoiding a race condition. But in investigating that possibility I added lots of NSLog statements everywhere something critical was happening... and the problem went away. So it clearly wasn't a timing issue. Looking back over the contents of the NSLog statements I realized that some of the values were being lazy-loaded, and the act of referencing them in the NSLog statements was causing them to be loaded. Similarly, while single-stepping through the code, I suspect that "Print description of..." commands were having the same effect (maybe).
So in my case, the UIDocument subclass builds a file wrapper that contains two files, one for metadata about the document and another that is the actual document data. There was a test to verify minimal correctness in the document, and this test used values from the metadata file which were meant to be lazy loaded but had never been accessed, so the test determined the file was not valid and set up the initial values all over again, wiping out the two items I was prepopulating the file with.

Related

xCode 7.0 IOS9 SDK: deadlock while executing fetch request with performBlockAndWait

Updated: I have prepared the sample which is reproduce the issue without magical record.Please download the test project using following URL:
https://www.dsr-company.com/fm.php?Download=1&FileToDL=DeadLockTest_CoreDataWithoutMR.zip
The provided project has following problem: deadlock on fetch
in performBlockAndWait called from main thread.
The issue is reproduced if code is compiled using XCode version > 6.4.
The issue is not reproduced if code is compiled using xCode == 6.4.
Old question was:
I am working on the support of IOS mobile application.
After the recent update of Xcode IDE from version 6.4 to version 7.0 ( with IOS 9 support ) I have faced with critical issue - application hangup.
The same build of the application ( produced from the same sources ) with xCode 6.4 works OK.
So, if the application is built using xCode > 6.4 - application hangs up on some cases.
if the application is built using xCode 6.4 - application works OK.
I have spent some time to research the issue and as the result I have prepared the test application with similar case like in my application which reproduces the problem.
The test application hangup on the Xcode >= 7.0 but works correctly on the Xcode 6.4
Download link of test sources:
https://www.sendspace.com/file/r07cln
The requirements for the test application is:
1. cocoa pods manager must be installed in the system
2. MagicalRecord framework of version 2.2.
Test application works in the following way:
1. At the start of the application it creates test database with 10000 records of simple entities and saves them to persistent store.
2. At the first screen of the application in the method viewWillAppear: it runs the test which causes deadlock.
Following algorithm is used:
-(NSArray *) entityWithId: (int) entityId inContext:(NSManagedObjectContext *)localContext
{
NSArray * results = [TestEntity MR_findByAttribute:#"id" withValue:[ NSNumber numberWithInt: entityId ] inContext:localContext];
return results;
}
…..
int entityId = 88;
NSManagedObjectContext *childContext1 = [NSManagedObjectContext MR_context];
childContext1.name = #"childContext1";
NSManagedObjectContext *childContext2 = [NSManagedObjectContext MR_context];
childContext2.name = #"childContext2";
NSArray *results = [self entityWithId:entityId inContext: childContext2];
for(TestEntity *d in results)
{
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name); /// this line is the reason of the hangup
}
dispatch_async(dispatch_get_main_queue(), ^
{
int entityId2 = 11;
NSPredicate *predicate2 = [NSPredicate predicateWithFormat:#"id=%d", entityId2];
NSArray *a = [ TestEntity MR_findAllWithPredicate: predicate2 inContext: childContext2];
for(TestEntity *d in a)
{
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name);
}
});
Two managed object contexts are created with concurrency type == NSPrivateQueueConcurrencyType (please check the code of MR_context of magical record framework). Both contexts has parent context with
concurrency type = NSMainQueueConcurrencyType. From the main thread application performs fetch in sync manner ( MR_findByAttribute and MR_findAllWithPredicate
are used performBlockAndWait with fetch request inside ). After the first fetch the second fetch is schedule on the main thread using dispatch_async().
As a result the application hangs up. It seems that deadlock has happened, please check the screenshot of the stack:
 here is the link, my reputation is too low to post images. https://cdn.img42.com/34a8869bd8a5587222f9903e50b762f9.png)
If to comment the line
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name); /// this line is the reason of the hangup
(which is the line 39 in ViewController.m of the test project ) the application becomes working OK. I believe this is because there is no read of name field of the test entity.
So with the commented line
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name);
there is no hangup on binaries built both with Xcode 6.4 and Xcode 7.0.
With the uncommented line
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name);
there is hangup on binary built with Xcode 7.0 and there is no hangup on binary built with Xcode 6.4.
I believe the issue is happens because of lazy-loading of entity data.
Has anybody problem with the described case? I will be grateful for any help.
This is why I don't use frameworks that abstract (i.e., hide) too many details of core data. It has very complex use patterns, and sometimes you need to know the details of how they interoperate.
First, I know nothing about magical record except that lots of people use it so it must be pretty good at what it does.
However, I immediately saw several completely wrong uses of core data concurrency in your examples, so I went and looked at the header files to see why your code made the assumptions that it does.
I don't mean to bash you at all, though this may seem like it at first blush. I want to help educate you (and I used this as an opportunity to take a peek at MR).
From a very quick look at MR, I'd say you have some misunderstandings of what MR does, and also core data's general concurrency rules.
First, you say this...
Two managed object contexts are created with concurrency type ==
NSPrivateQueueConcurrencyType (please check the code of MR_context of
magical record framework). Both contexts has parent context with
concurrency type = NSMainQueueConcurrencyType.
which does not appear to be true. The two new contexts are, indeed, private-queue contexts, but their parent (according to the code I glanced at on github) is the magical MR_rootSavingContext, which itself is also a private-queue context.
Let's break down your code example.
NSManagedObjectContext *childContext1 = [NSManagedObjectContext MR_context];
childContext1.name = #"childContext1";
NSManagedObjectContext *childContext2 = [NSManagedObjectContext MR_context];
childContext2.name = #"childContext2";
So, you now have two private-queue MOCs (childContext1 and childContext2), both children of another anonymous private-queue MOC (we will call savingContext).
NSArray *results = [self entityWithId:entityId inContext: childContext2];
You then perform a fetch on childContext1. That code is actually...
-(NSArray *) entityWithId:(int)entityId
inContext:(NSManagedObjectContext *)localContext
{
NSArray * results = [TestEntity MR_findByAttribute:#"id"
withValue:[NSNumber numberWithInt:entityId]
inContext:localContext];
return results;
}
Now, we know that the localContext in this method is, in this case, another pointer to childContext2 which is a private-queue MOC. It is 100% against the concurrency rules to access a private-queue MOC outside of a call to performBlock. However, since you are using another API, and the method name offers no assistance to know how the MOC is being accessed, we need to go look at that API and see if it hides the performBlock to see if you are accessing it correctly.
Unfortunately, the documentation in the header file offers no indication, so we have to look at the implementation. That call ends up calling MR_executeFetchRequest... which does not indicate in the documentation how it handles the concurrency either. So, we go look at its implementation.
Now, we are getting somewhere. This function does try to safely access the MOC, but it uses performBlockAndWait which will block when it is called.
This is an extremely important piece of information, because calling this from the wrong place can indeed cause a deadlock. Thus, you must be keenly aware that performBlockAndWait is being called anytime you execute a fetch request. My own personal rule is to never use performBlockAndWait unless there is absolutely no other option.
However, this call here should be completely safe... assuming it is not being called from within the context of the parent MOC.
So, let's look at the next piece of code.
for(TestEntity *d in results)
{
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name); /// this line is the reason of the hangup
}
Now, this is not the fault of MagicalRecord, because MR isn't even being used directly here. However, you have been trained to use those MR_ methods, which require no knowledge of the concurrency model, so you either forget or never learn the concurrency rules.
The objects in the results array are all managed objects that live in the childContext2 private-queue context. Thus, you may not ever access them without paying homage to the concurrency rules. This is a clear violation of the concurrency rules. While developing your application, you should enable concurrency debugging with the argument -com.apple.CoreData.ConcurrencyDebug 1.
This code snippet must be wrapped in either performBlock or performBlockAndWait. I hardly ever use performBlockAndWait for anything because it has so many drawbacks - deadlocks being one of them. In fact, just seeing the use of performBlockAndWait is a very strong indication that your deadlock is happening in there and not on the line of code that you indicate. However, in this case, it is at least as safe as the previous fetch, so let's make it a bit safer...
[childContext2 performBlockAndWait:^{
for (TestEntity *d in results) {
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name);
}
}];
Next, you dispatch to the main thread. Is that because you just want something to occur on a subsequent event loop cycle, or is it because this code is already running on some other thread? Who knows. However, you have the same problem here (I reformatted your code for readability as a post).
dispatch_async(dispatch_get_main_queue(), ^{
int entityId2 = 11;
NSPredicate *predicate2 = [NSPredicate predicateWithFormat:#"id=%d", entityId2];
NSArray *a = [TestEntity MR_findAllWithPredicate:predicate2
inContext:childContext2];
for (TestEntity *d in a) {
NSLog(#"e from fetchRequest %# with name = '%#'", d, d.name);
}
});
Now, we know that code starts out running on the main thread, and the search will call performBlockAndWait but your subsequent access in the for-loop again violates the core data concurrency rules.
Based on that, the only real problems I see are...
MR seems to honor the core data concurrency rules within their API, but you must still follow the core data concurrency rules when accessing your managed objects.
I really don't like the use of performBlockAndWait as it's just a problem waiting to happen.
Now, let's take a look at the screenshot of your hang. Hmmm... it's a classic deadlock, but it makes no sense because the deadlock happens between the main thread and the MOC thread. That can only happen if the main-queue MOC is a parent of this private-queue MOC, but the code shows that is not the case.
Hmmm... it didn't make sense, so I downloaded your project, and looked at the source code in the pod you uploaded. Now, that version of the code uses the MR_defaultContext as the parent of all MOCs created with MR_context. So, the default MOC is, indeed, a main-queue MOC, and now it all makes perfect sense.
You have a MOC as a child of a main-queue MOC. When you dispatch that block to the main queue, it's is now running as a block on the main queue. The code then calls performBlockAndWait on a context that is a child of a MOC for that queue, which is a huge no-no, and your are almost guaranteed to get a deadlock.
So, it seems that MR has since changed their code from using a main-queue as the parent of new contexts to using a private-queue as the parent of new contexts (most likely due to this exact problem). So, if you upgrade to the latest version of MR you should be fine.
However, I would still warn you that if you want to use MR in multithreading ways, you must know exactly how they handle the concurrency rules, and you must also make sure you obey them anytime you are accessing any core-data objects that are not going through the MR API.
Finally, I'll just say that I've done tons and tons of core data stuff, and I've never used an API that tries to hide the concurrency issues from me. The reason is that there are too many little corner cases, and I'd rather just deal with them in a pragmatic way up front.
Finally, you should almost never use performBlockAndWait unless you know exactly why its the only option. Having it be used as part of an API underneath you is even more scary... to me at least.
I hope this little jaunt has enlightened and helped you (and possible some others). It certainly shed a little bit of light for me, and helped reestablish some of my previous unfounded skittishness.
Edit
This is in response to the "non-magical-record" example you provided.
The problem with this code is the exact same problem I described above, relative to what was happening with MR.
You have a private-queue context, as a child to a main-queue context.
You are running code on the main queue, and you call performBlockAndWait on the child context, which has to then lock its parent context as it tries to execute the fetch.
It is called a deadlock, but the more descriptive (and seductive) term is deadly embrace.
The original code is running on the main thread. It calls into a child context to do something, and it does nothing else until that child complete.
That child then, in order to complete, needs the main thread to do something. However, the main thread can't do anything until the child is done... but the child is waiting for the main thread to do something...
Neither one can make any headway.
The problem you are facing is very well documented, and in fact, has been mentioned a number of times in WWDC presentations and multiple pieces of documentation.
You should NEVER call performBlockAndWait on a child context.
The fact that you got away with it in the past is just a "happenstance" because it's not supposed to work that way at all.
In reality, you should hardly every call performBlockAndWait.
You should really get used to doing asynchronous programming. Here is how I would recommend you rewrite this test, and whatever it is like that prompted this issue.
First, rewrite the fetch so it works asynchronously...
- (void)executeFetchRequest:(NSFetchRequest *)request
inContext:(NSManagedObjectContext *)context
completion:(void(^)(NSArray *results, NSError *error))completion
{
[context performBlock:^{
NSError *error = nil;
NSArray *results = [context executeFetchRequest:request error:&error];
if (completion) {
completion(results, error);
}
}];
}
Then, you change you code that calls the fetch to do something like this...
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity: testEntityDescription ];
[request setPredicate: predicate2 ];
[self executeFetchRequest:request
inContext:childContext2
completion:^(NSArray *results, NSError *error) {
if (results) {
for (TestEntity *d in results) {
NSLog(#"++++++++++ e from fetchRequest %# with name = '%#'", d, d.name);
}
} else {
NSLog(#"Handle this error: %#", error);
}
}];
We switched over to XCode7 and I just ran into a similar deadlock issue with performBlockAndWait in code that works fine in XCode6.
The issue seems to be an upstream use of dispatch_async(mainQueue, ^{ ... to pass back the result from a network operation. That call was no longer needed after we added concurrency support for CoreData, but somehow it was left and never seemed to cause a problem until now.
It's possible that Apple changed something behind the scenes to make potential deadlocks more explicit.

MagicalRecord saveWithBlock vs saveToPersistentStoreAndWait

I am trying very hard to understand everything about MagicalRecord and CoreData. So let's say, I have 2 pieces of code doing same thing, where tallyM is a managed object running in MR_defaultContext.
Option 1:
Tally *tallyM = (Tally *)[Tally MR_findFirstWithPredicate:predicateM];
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
Tally *tallyMLocal = [tallyM MR_inContext:localContext];
tallyMLocal.tl_countMale = [NSString stringWithFormat:#"%ld", (long)uiTallyMaleCounter];
} completion:^(BOOL success, NSError *error) {
[self updateTallies_APICall:[tallyM MR_inContext:[NSManagedObjectContext MR_defaultContext]]];
}];
Option 2:
Tally *tallyM = (Tally *)[Tally MR_findFirstWithPredicate:predicateM];
tallyM.tl_countMale = [NSString stringWithFormat:#"%ld", (long)uiTallyMaleCounter];
[tallyM.managedObjectContext MR_saveToPersistentStoreAndWait];
[self updateTallies_APICall:[tallyM MR_inContext:[NSManagedObjectContext MR_defaultContext]]];
Questions:
Which one is better? I understand that saveWithBlock can be used when you need async save, but is there any other difference? Is Option 1 safer or better in any way than Option 2?
In Option 1, I have tallyM which runs in MR_defaultContext. Then inside saveWithBlock, I change tallyM, by changing tallyMLocal, and saving contexts. Can I be 100% sure that after saveWithBlock runs, in completion handler (when I need to continue working with tallyM), tallyM (which is still running in MR_defaultContext) will have the tl_countMale updated?
In Option 1, in completion handler, do I still need to call below code? I assume (already checked with console, but just want to be sure) that tallyM still runs in MR_defaultContext, after saveWithBlock is executed. So is it needed to call again MR_inContext?
[tallyM MR_inContext:[NSManagedObjectContext MR_defaultContext]]
Let's say I don't need async save at all. So I can use Option 2, or saveWithBlockAndWait. Is saveWithBlockAndWait in any way better than Option 2?
I just want to make sure I finally correctly understood how MagicalRecords and CoreData behaves.
Personally, I would avoid the pattern in Option 2 there. The idea being that you should use a single Managed Object Context as the scope for operations on a collection of Managed Objects. That is why most examples use the following pattern:
NSManagedObjectContext *localContext = //...;
NSManagedObject *localObject = [otherObject MR_inContext:localContext];
///make changes to localObject
[localContext MR_saveToPersistentStoreAndWait];
The [MagicalRecord saveWithBlock:] method basically implements this pattern in a more convenient API.
I would also recommend not using the defaultContext implicitly. Be more explicit about that in your code because you may need to swap that out when your app starts to deal with threads.
The completion handlers are written in a way that they are always called back after the save operation is 100% complete. I recommend reading the source code to see for yourself.

Model object and Core Data

I have an object that I load up data from Core Data. I then modify the object with user inputs/choices.
My first though was to override the setter methods for the properties:
-(void)setType:(NSString *)type {
NSLog(#"setType fired | newType: %#", type);
_type = type;
appDelegate *appDelegate = (appDelegate *)[[UIApplication sharedApplication] delegate];
NSManagedObjectContext *context = [appDelegate managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:DEFAULTS_DB];
NSError *error;
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
if (fetchedObjects.count == 1) {
Defaults *defaults = [fetchedObjects objectAtIndex:0];
defaults.sceneType = type;
}
if (![context save:&error]) {
NSLog(#"Error in saving first run defaults | error: %#", error);
}
else {
NSLog(#"new type was saved to core data");
}
}
My other thought was to update the Core Data when applicationWillResignActive: fires (but that method only gets a few seconds to run before the app is frozen) and when the user logs out.
The app i'm creating is one that the user would start up, set up what he wants, then puts it down 10-60min until he uses it again so i'm concerned with my app being killed while inactive and loosing the data.
Is updating core data in the setter method a good way to handle updates or is it a really bad idea (too resource intensive, too slow)?
It's not a typical usage pattern. Typical would be to fetch your object before displaying its data and hold it. Then when the user changes something, update object properties and save the context.
It sort of depends on how much amount of data you are setting and retrieving with each call to your customer setters. I'd try what you are doing now (updating core data in setters) but test it out on an old device, say an iPad 1, and see how it performs. After playing it out for a while, you can decide whether you want to update core data with every setter or not.
Now, if you don't see any performance difference at all, I wouldn't worry about it. You're good. You are having the comfort of being able to save the most updated actions from the user by committing your data in setters. However, there might come a point when you are saving more data and/or large files/images and the earlier devices start to see a difference in performance.
In order to be prepared for such a situation in advance, I'd suggest having a buffer (that mirrors the structure of your entity) in your program that gets written to core data every so often - may be when the app goes into a state of inactivity or if the app goes into background or for every fixed time period. It's imperative the buffer gets updated in the setters. The possible hiccup with your idea of writing code in applicationWillResignActive: stems from how prepared you are at handling crashes. Crashes can happen any time for any reason, sometimes maybe not because of your own bad code. And this is one strong reason why having buffers is a good idea. You either lose one chunk of small data during a crash (worst case) or you achieve performance + consistency (best case).

I can't make a new instance of NSManagedObject on background thread with non-main MOC

I have researched a ton of posts regarding Core Data on background threads, and I feel like I understand (on paper) what needs to be going on. I guess we'll see. I am working on migrating an existing OS X app to Core Data, and am having issues making new instances of my NSManagedObject on an async thread.
Here is a sample of the code I am running right after I have moved onto a background thread:
NSLog(#"JSON 1");
NSManagedObjectContext * context = [[NSManagedObjectContext alloc] init];
[context setPersistentStoreCoordinator:[[NSApp delegate] persistentStoreCoordinator]];
asset = (MTAssetInfo*)[NSEntityDescription insertNewObjectForEntityForName:#"Info" inManagedObjectContext:context];
NSLog(#"JSON 2");
The result is that the first log message (#"JSON 1") gets called 31 times, and the second one (#"JSON 2") is never called. The object isn't being made and returned correctly.
The model for this Info entity is quite complex with a few transformable attributes that may or may not be setup correctly. The weird thing is that similar code run on the main thread and the main MOC works great. No issues.
EDIT - Some more context
The async call originates from here:
for (NSNumber *sectionID in sectionsToShow) {
dispatch_group_async(group, queue, ^{
MTAssetInfo *asset = [self assetWithRefID:[sectionID unsignedIntegerValue]];
if (asset != nil) {
[sectionsLock lock];
[sectionsTemp addObject:asset];
[sectionsLock unlock];
}
});
}
The assetWithRefID method never returns with an object because of the other code snippet. It never successfully pulls an NSManagedObject out of the context on the background thread.
You are going to have to provide more information to get real help, but I bet your problem is an error happening in the NSManagedDocument background thread.
I'd register a NSNotificationCenter for ALL messages (name:nil object:nil) and just print them out. I bet you see a status change or error message in there that is failing.
You might want to try a #try/#catch block around it just to see if exceptions are being thrown.
Maybe it will give you more to go on.
One other suggestion... Swizzling isn't necessarily the right tool for production stuff, but it's almost unbeatable for debugging. I have method-swizled several entire classes, so that it sends a detailed NSNotification before/after each invocation.
It has saved me tons of time, and helped me track down some wicked bugs. Now, when something is going on in CoreData, I take out my set of classes, link them in, and see all the detail I want.
I know that does not exactly answer you question, but hopefully it will put you on the track so you can provide some more information and get it all fixed.
If that's too much for you, create a subclass and instantiate that, with a similar method for calling super. You can get a real idea of the entire flow pretty easily.

How can I detect that iCloud has finished downloading the document, as well as run the completion handler?

When loading a document from iCloud, one must make a call to
openWithCompletionHandler:^(BOOL success)completionHandler
This function will start a background thread that download the file from iCloud, and upon finishing the load, runs the completion handler.
While that's happening, any code after this call continues running.
How can I stop the program from continuing to run until after the download is complete?
Immediately after making a call to load from the cloud, my code tries to use the document - but of course, since it isn't finished downloading, the code crashes.
Details follow:
I'm currently working on a save-file library to handle saving/loading of files, encryption, compression, and iCloud support. Users make a call to my library function LoadFileAtPath and there is a parameter specifying if they want me to check iCloud for this particular file.
When the function starts and I am meant to check on iCloud, the first thing I do is make a call to my iCloudload function, like so:
bool cloudLoad = [iCloudStorageManager readFileFromiCloud:filePath name:fileName];
within this function I make the call to openWithCompletionHandler, like so:
if ([fileManager fileExistsAtPath:[docURL path]])
{
[doc openWithCompletionHandler:^(BOOL success){
if (!success)
{
// Handle the error.
NSLog(#"Failed to retrieve document:%# from iCloud URL:%#.", fileName, [docURL absoluteString]);
}
else
{
NSLog(#"Replacing document in sandbox with iCloud version");
BOOL* dir = nil;
if (![fileManager fileExistsAtPath:filePath isDirectory:dir])
{
NSError *fileError = nil;
if(![fileManager createDirectoryAtPath:filePath withIntermediateDirectories:YES attributes:nil error:&fileError])
{
NSLog(#"Error creating file directory: %#\n%#\n%#\n%#", [fileError localizedDescription], [fileError localizedFailureReason], [fileError localizedRecoveryOptions], [fileError localizedRecoverySuggestion]);
}
}
// save new data if success
[iCloudStorage replaceDocumentInSandboxWith:doc newData:doc.loadedContents];
}
}];
[doc release];
}
After that, my code continues by trying to pull up the data, and do various things with it such as decrypt, decompress, and hand the file data to the caller.
My current (hacky) solution was to have, after the initial call to readFileFromiCloud, an loop that checks a bool, like so:
while (!cloudDidFinishLoad)
{
sleep(10);
}
This bool is initialized to false, and within the function seen above "replaceDocumentInSandboxWith", the bool is set to true.
However, I have found that this causes the program to hang, it never finishes loading the iCloud file, and the completion handler never gets called.
I'm at a loss as to what I should do. I need the program to stop running code until the download is finished, but I don't know how to do this.
Not sure if you found an answer to this or not, but what I would do is create a protocol for your library and then set up a delegate that you can make a call to when the completion handler finishes.
Then in your main controller can be set up as the delegate and once the file is ready you can receive the call from the library that the file is ready to use. So the pseudo code would be something like this...
Create iCloudStorageManager
Set self as delegate of iCloudStorageManager
Call the file open on the iCloudStorageManager
Do whatever you need to do here, set up activity indicator or lock out the interface or neither and just assume it worked unless the delegate tells you it didn't. Basically here your block will end and when the delegate function is called your main controller will pick back up control of the interface.
In the delegate function you will receive the status from the iCloudStorageManager of whether it was successful or not. Once you get that call from the iCloudStorageManager you can free up the interface, post an alert that things went well or that things went south and offer a reply...whatever you want to do.
But that is the way I would handle it. (Yes this is an old question, but I felt like I had some insight :))
Freezing the User Interface (via that sleep call on the main thread) while waiting for a file to finish downloading seems really harsh to me, and I'd expect your customers aren't going to like that.
Why not throw up an activity spinner, like:
And then take it away when your iCloud completion handler is called? While the activity view is on screen, you can disable the rest of the UI interaction via UIView's userInteractionEnabled property (being set to FALSE).

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