ok, when your app first starts, I would suggest checking whether 1. your database exists (if it doesn't, you alloc init it) and 2. if the document doesn't exist (on disk), is closed or is open.
here's how you could do this:
looks like you are using a singleton for your database, so when your first view controller comes up, check whether the Managed Document has been alloc inited, so in ViewWillAppear:
if (!dataBase)
{
NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
url = [url URLByAppendingPathComponent:@"Your DB Name"];
self.dataBase=[[UIManagedDocument alloc]initWithFileUrl:url];
}
so now if the database (UIManagedDocument) has been alloc inited, it still does not mean that the actual database file has been created on disk. You have to check for it as follows (and you could do this in a setter for your database or in ViewDidLoad, but don't do it in another thread because it won't work)
so you are checking for 3 cases here: does not exist
if (![[NSFileManager defaultManager]fileExistsAtPath:[yourManagedDocumentFromSingleton.fileUrl path])
{
[[NSFileManager defaultManager]fileExistsAtPath:[yourManagedDocumentFromSingleton saveToUrl:[[NSFileManager defaultManager]fileExistsAtPath:[yourManagedDocumentFromSingleton.fileUrl forSaveOperation:UIDocumentSaveForCreating completionHandler:
^(BOOL success){ now you can use your uidocument and its managed object context}];
}
if file does exist but is closed:
else if (yourManagedDocumentFromSingleton.documentState==UIDocumentStateClosed)
{
[yourManagedDocumentFromSingleton openWithCompletionHandler:
^(BOOL success) {use your document here}];
}
finally if the document is already open, just use it:
else if (yourManagedDocumentFromSingleton.documentState=UIDocumentStateNormal)
{
//do whatever with the document
}
one important thing to mention is that UIDocument is not thread safe. So it must be used and checked in the same thread that it was created (presumably main thread here). Otherwise it will not work.
I don't know the exact structure of your view controller or singleton but if you follow these steps it will work.
PS. Also make sure that once your doc is up and running and you're adding items to it or removing, save it after each operation so your NSFetchedResultsController gets updated. CoreData does have autosave but I found that I had to manually save for things to work properly. You can save with (from previous method):
forSaveOperation:UIDocumentSaveForOverwriting