iOS CoreData Array仅在我重新启动应用程序时显示

Question

I have a simple Grocery List app where I add items to the list. I want to save these items with Core Data so that the data is saved when the app is terminated.

I simply want to display all data, so if I understand correctly I don't need to implement an NS-FetchedResultsController for this.

Right now, items are successfully adding in my CoreData, but the list only refreshes when I exit the app and re-open it.

So far I've tried putting [self.tableView reloadData] , [[self tableView] reloadData] and [self.tableView reloadRowsAtIndexPaths:groceryArray withRowAnimation:YES]; in all the locations I could think of, including the viewDidLoad method, the unwindToSegue method that's coming from the Add Grocery Item List view controller, and also implementing a viewWillAppear method as well.

My mainAppDelegate code is straight from Apple and a tutorial... so I don't think this code is the problem. All properties and files are imported correctly.

My data entity is entitled "Item" and i have one single attribute titled "toDoItems" (type: string).

my TableViewController code which displays the list of data (and is not refreshing):

@interface XYZToDoListViewController ()
@end

@implementation XYZToDoListViewController
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
@synthesize groceryArray;


- (IBAction)unwindToList:(UIStoryboardSegue *)segue
{
    [[self tableView] reloadData];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    mainAppDelegate *appDelegate = [[UIApplication sharedApplication]delegate];
    _managedObjectContext = [appDelegate managedObjectContext];

    NSFetchRequest *request = [[NSFetchRequest alloc]init];
    NSEntityDescription *items = [NSEntityDescription entityForName:@"Item" inManagedObjectContext:_managedObjectContext];
    [request setEntity:items];

    NSError *error = nil;
    NSMutableArray *mutableFetchResults = [[_managedObjectContext executeFetchRequest:request error:&error]mutableCopy]; if (mutableFetchResults == nil){
    //handle error
    }
    [self setGroceryArray:mutableFetchResults];


    [[self tableView] reloadData];    
    }

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle
forRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        NSManagedObject *eventToDelete = [ groceryArray objectAtIndex:indexPath.row];
        [_managedObjectContext deleteObject: eventToDelete];

        [groceryArray removeObjectAtIndex:indexPath.row];
        [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:YES];
        NSError *error = nil;
        if (![_managedObjectContext save:&error])
        { //handle error 
        }
    }
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection: (NSInteger)section
{

    return [groceryArray count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = @"ListPrototypeCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];

Item *items = (Item *) [groceryArray objectAtIndex:indexPath.row];
cell.textLabel.text = [items toDoItems];
return cell;
}

@end

My Add New Item view controller:

@interface XYZAddItemViewController ()
@property (strong, nonatomic) IBOutlet UIBarButtonItem *doneButton;

@end

@implementation XYZAddItemViewController
@synthesize textField;
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;


- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
Item *item = [NSEntityDescription insertNewObjectForEntityForName:@"Item" inManagedObjectContext:_managedObjectContext];
[item setToDoItems:textField.text];
NSLog (@"Item Added");
NSError *error = nil;
if (![_managedObjectContext save:&error])
    { //handle error }
        textField.text = NULL;
}

}

- (BOOL)shouldPerformSegueWithIdentifier:(NSString *)segue sender:(id)sender {
if (self.textField.text.length > 0)
{
    return YES;
}
else {
    return NO;
}
} 

- (void)viewDidLoad
{
[super viewDidLoad];
mainAppDelegate *appDelegate = [[UIApplication sharedApplication]delegate];
_managedObjectContext = [appDelegate managedObjectContext];

self.navigationController.view.backgroundColor =
[UIColor colorWithPatternImage:[UIImage imageNamed:@"bg_white.png"]];
self.view.backgroundColor = [UIColor clearColor];
}

-(BOOL)textFieldShouldReturn:(UITextField *)textField{
[textField resignFirstResponder];
return YES;
}

@end

What do I need to change to get the table view controller to refresh?

Answer 1

You have to execute the fetch request again after an item has been added, and assign the result to your data source array groceryArray , before calling reloadData .

Otherwise reloadData has only the effect that the same old data is displayed again.

(This is what a fetched results controller would manage for you.)

Answer 2

The data for your UITableView comes from groceryArray.

You are inserting the objects correctly into CoreData, but your tableView is still looking to the groceryArray that you fetched at the start.

So when you add something, you need to run the fetch request again, save it to groceryArray, and THEN do a reloadData. That way it should reflect the changes.