Update Core Data without having to change screen - ios

Question

After I update my Core Data store - by deleting then adding the data - in a different thread, I'm required to change the screen and then go back for the data to update it. Is there a way to do update Core Data without having to change the screen in the app?
code to reset database:
- (void) resetDatabase {
count++;
dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
ConDAO *con = [[ConDAO alloc] init];
DatabaseManager *manager = [DatabaseManager sharedManager];
NSError * error;
NSURL * storeURL = [[[manager managedObjectContext] persistentStoreCoordinator] URLForPersistentStore:[[[[manager managedObjectContext] persistentStoreCoordinator] persistentStores] lastObject]];
[[manager managedObjectContext] reset];//to drop pending changes
if ([[[manager managedObjectContext] persistentStoreCoordinator] removePersistentStore:[[[[manager managedObjectContext] persistentStoreCoordinator] persistentStores] lastObject] error:&error])
{
// remove the file containing the data
[[NSFileManager defaultManager] removeItemAtURL:storeURL error:&error];
//recreate the store like in the appDelegate method
[[[manager managedObjectContext] persistentStoreCoordinator] addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error];//recreates the persistent store
}
NSLog(#"*****************************");
NSLog(#"updating");
NSLog(#"count: %d", count);
NSLog(#"*****************************");
[self populateDatabase:0 con:con];
NSTimer *timer = [NSTimer timerWithTimeInterval:60.0
target:self
selector:#selector(resetDatabase)
userInfo:nil repeats:NO];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
dispatch_async(dispatch_get_main_queue(), ^(void){
});
});
}
Code that runs when ui is changed:
- (void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:animated];
// Setup KVO for verifyingcard
[self addObserver:self forKeyPath:#"verifyingCard" options:NSKeyValueObservingOptionNew context:nil];
if([BluetoothTech isEqualToString:#"BLE"]){
self.centralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil options:#{CBCentralManagerOptionShowPowerAlertKey: #YES}];
}
else if([BluetoothTech isEqualToString:#"HID"]){
[self.bluetoothScanTextView becomeFirstResponder];
}
[self loadStudents];
}
I think it has to do with the loadStudents() function, but when I use NSNotificationCenter to run it from the other class, it still doesnt work.
LoadStudent code:
- (void)loadStudents{
NSError *error = nil;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"Caf_student_cards"];
NSArray *arr = [[self.manager managedObjectContext] executeFetchRequest:fetchRequest error:&error];
for(int i = 0; i < [arr count]; i++){
if([[[arr objectAtIndex:i] valueForKey:#"user_id"] isEqualToString:#"201509061"]){
NSLog(#"%#",[arr objectAtIndex:i]);
}
}
if(!error){
self.caf_student_cards = [NSMutableArray arrayWithArray:arr];
self.keys = [[[arr.firstObject entity] attributesByName] allKeys];
}
else{
NSLog(#"%s %s %s","\n\n\n",[[error localizedDescription] UTF8String],"\n\n\n");
dispatch_async(dispatch_get_main_queue(), ^{
// Show alert to tell user to reload this page
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:#"Error: %#", [error localizedDescription]] message:#"Check connection and relog back into cafeteria." delegate:nil cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
});
}
}

Answer 1

There are multiple problems with this code.
The one most directly relevant to your question is that you're updating your persistent store, but not updating your UI. It doesn't happen automatically. If you have new data, you need to tell your UI to update. How to do that depends on what kind of UI you have. If it's a table view, it might be as simple as telling the table view to reload its data. If you have an array that you use to hold the UI's data, you would need to update that too (it looks like this might be what caf_student_cards is in your code but it's impossible to be sure.
Other problems-- and these are major problems that you need to fix immediately:
You're doing Core Data multithreading wrong. Using dispatch_async is not effective here. You need to use performBlock or performBlockAndWait on your managed object context, or else performBackgroundTask on your persistent container.
You're removing the main persistent store file but not removing the journal files. This is pretty much guaranteed to either prevent old data from being deleted or else simply cause data corruption. What you're doing is not a useful technique. Removing the persistent store files is rarely a good idea. If you want to get rid of existing data, delete it from Core Data, maybe by telling your context to delete the objects or else by using NSBatchDeleteRequest.
There may be others. This code is a mess. You would be doing yourself a huge favor if you spent a little time looking over Apple's Core Data Programming Guide.
Also you keep asking nearly the same question repeatedly. You've had some good advice, but you don't seem to be taking any of it. If you want more information, go and read over other answers people have already given when you've posted this question before.