What should the logic for first run, internet available be? - ios

Question

For an app that fetches web from a web service, I have included a plist to be parsed into CoreData if its the first run because the data is not readily available in the Docs directory or may take long to fetch from the web. I do have NSNotifications signaling when a web fetch/synchronization has succeeded though.
At present in AppDelegate applicationDidFinishLaunchingWithOptions I call:
[self checkIfFirstRun];
which is this:
-(void)checkIfFirstRun{
NSString *bundleVersion = [[NSBundle mainBundle] objectForInfoDictionaryKey:(NSString *)kCFBundleVersionKey];
NSString *appFirstStartOfVersionKey = [NSString stringWithFormat:#"first_start_%#", bundleVersion];
NSNumber *alreadyStartedOnVersion = [[NSUserDefaults standardUserDefaults] objectForKey:appFirstStartOfVersionKey];
if(!alreadyStartedOnVersion || [alreadyStartedOnVersion boolValue] == NO) {
// IF FIRST TIME -> Preload plist data
UIAlertView *firstRun = [[UIAlertView alloc] initWithTitle:#"1st RUN USE LOCAL DB"
message:#"FIRST"
delegate:self
cancelButtonTitle:#"Cancel"
otherButtonTitles:#"Ok", nil];
[firstRun show];
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
[prefs setObject:[NSNumber numberWithBool:YES] forKey:appFirstStartOfVersionKey];
[prefs synchronize];
//Use plist
[self parsePlistIntoCD];
} else {
UIAlertView *secondRun = [[UIAlertView alloc] initWithTitle:#"nTH RUN WEB FETCH"
message:#"nTH"
delegate:self
cancelButtonTitle:#"Cancel"
otherButtonTitles:#"Ok", nil];
[secondRun show];
}
}
So ok, i get my plist parsed perfectly into my CoreData db.
Here is the parsePlistIntoCD:
-(void)parsePlistIntoCD{
self.managedObjectContext = [[SDCoreDataController sharedInstance] backgroundManagedObjectContext];
// 3: Now put the plistDictionary into CD...create get ManagedObjectContext
NSManagedObjectContext *context = self.managedObjectContext;
NSError *error;
//Create Request & set Entity for request
NSFetchRequest *holidayRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *topicEntityDescription = [NSEntityDescription entityForName:#"Holiday" inManagedObjectContext:context];
[holidayRequest setEntity:topicEntityDescription];
//Create new NSManagedObject
//Holiday *holidayObjectToSeed = nil;
Holiday *newHoliday = nil;
//Execute fetch just to make sure?
NSArray *holidayFetchedArray = [context executeFetchRequest:holidayRequest error:&error];
if (error) NSLog(#"Error encountered in executing topic fetch request: %#", error);
// No holidays in database so we proceed to populate the database
if ([holidayFetchedArray count] == 0) {
//Get path to plist file
NSString *holidaysPath = [[NSBundle mainBundle] pathForResource:#"PreloadedFarsiman" ofType:#"plist"];
//Put data into an array (with dictionaries in it)
NSArray *holidayDataArray = [[NSArray alloc] initWithContentsOfFile:holidaysPath];
NSLog(#"holidayDataArray is %#", holidayDataArray);
//Get number of items in that array
int numberOfTopics = [holidayDataArray count];
//Loop thru array items...
for (int i = 0; i<numberOfTopics; i++) {
//get each dict at each node
NSDictionary *holidayDataDictionary = [holidayDataArray objectAtIndex:i];
//Insert new object
newHoliday = [NSEntityDescription insertNewObjectForEntityForName:#"Holiday" inManagedObjectContext:context];
//Parse all keys in each dict object
[newHoliday setValuesForKeysWithDictionary:holidayDataDictionary];
//Save and or log error
[context save:&error];
if (error) NSLog(#"Error encountered in saving topic entity, %d, %#, Hint: check that the structure of the pList matches Core Data: %#",i, newHoliday, error);
};
}
[[SDSyncEngine sharedEngine] startSync];
}
The thing is, I need to also make sure that if there is internet available, that my CoreData db get repopulated with the fetched web data.
But If I leave the call to [self parsePlistIntoCD]; only the plist data is present in the CoreData. First or nth run, I only get the plist data. If I comment that line out, I get my web fetched data.
Why doesnt the web fetched data replace the plist parsed data?

Answer 1

So the logic of parsePlistIntoCD is essentially
if no objects in store, load them from plist
always invoke startSync on [SDSyncEngine sharedEngine], which handles the web download and sync.
It looks to me like your startSync will in fact be invoked. So I would look there for the bug. You could add a log statement, or set breakpoints, to verify that that code path is actually being followed.
Both the plist parse and the web data fetch might take some time. That's a sign that you should be doing these operations in the background, perhaps with a GCD queue. You don't know in advance whether either of them will succeed. So don't set the preferences until they finish.
Side note: you can query the preferences database for BOOLs, making your code shorter, and therefore easier to read.
BOOL alreadyStartedOnVersion = [[NSUserDefaults standardUserDefaults] boolForKey:appFirstStartOfVersionKey];
and
[prefs setBool:YES forKey:appFirstStartOfVersionKey];
You can also replace numberWithBool: with simply #(YES) and #(NO).
For your program logic, I suggest something like this:
In -applicationDidFinishLaunchingWithOptions:, check to see if the starting plist data has been loaded. Forget about whether it's the first run. Just see whether the plist data needs to be loaded. Maybe call that shouldLoadPlistData. Or maybe you need to tie that to the version you're running, in which case you'd store a string latestPlistVersionLoaded.
If you haven't loaded it yet, enqueue a block to perform the plist load. At the conclusion of the plist load, set shouldLoadPlistData to NO, to note that plist data no longer needs to be loaded. If, for some reason, the plist load fails (maybe the phone runs out of battery or your app is killed by user or system), then on the next launch you're back where you started.
also check to see whether you have net access. If you do, enqueue a block to retrieve the web-based data, parse the data, and then, upon conclusion, update the preferences.
If the data is large, you might want to checkpoint this work:
Do I have the full web update? Then I'm done. Otherwise...
Has the download finished? Yay, I have the data, let's load it.
If not, have I started the download?
This staged checkpointing will also allow you to ask the system for extra time, if your app exits in the middle of the download.
parseListIntoCD feels a bit bloated to me. It does more than its name implies. Perhaps you could refactor it into a check (shouldLoadPlist), a method that does the import (importPlist:intoContext:), and a method that fires off the sync.
I strongly suggest that you pass the working NSManagedObjectContext in as a parameter, rather than having some global object that dispenses MOCs (as [SDCoreDataController sharedInstance] appears to do. It gives you much more control, and allows you to write unit tests much more easily. If you also pass in the path to the plist, you now have clean code that should behave the same way every time you call it.
Your use of the NSError ** parameter is consistently incorrect. The value of NSError is undefined upon success. You must test the result of the operation, not the value of the error, to determine whether you succeeded. The idiom is always
if (![someObject doTaskWithObject:foo error:&error]) {
// handle the error
}
Take a look also at countForFetchRequest:error. It would give you the same info that you're currently extracting by performing a fetch and counting results, but without having to instantiate the NSManagedObjects.