核心数据无法正确保存

Question

I'm using a data model called settings which I setup in didLoad of my viewController:

settings = [NSEntityDescription insertNewObjectForEntityForName:@"Settings" inManagedObjectContext:[self managedObjectContext]];

Heres the managedobjectContext method:

- (NSManagedObjectContext *)managedObjectContext {
NSManagedObjectContext *context = nil;
id delegate = [[UIApplication sharedApplication] delegate];
if ([delegate performSelector:@selector(managedObjectContext)]) {
    context = [delegate managedObjectContext];
}
return context;
}

When my stepper increments I want to update a string and then update the db.

- (IBAction)RowStepperAction:(UIStepper *)sender
{
    double value = [sender value];
    settings.numberofrows = [NSNumber numberWithDouble:value];
    [self.RowNumber setText:[NSString stringWithFormat:@"%d", (int)value]];

    NSError *error = nil;
    // Save the object to persistent store
    if (![[self managedObjectContext] save:&error]) {
        NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
    }
}

When I come to load the view again I do:

[self.ColumnStepper setValue:[settings.numberofcolumns doubleValue]];
[self.RowStepper setValue:[settings.numberofrows doubleValue]];

This returns the default values I set in the database. Why is this?

Answer 1

Every time you load the view again, you're creating a brand new settings object :

settings = [NSEntityDescription insertNewObjectForEntityForName:@"Settings" inManagedObjectContext:[self managedObjectContext]];

This will have your default values. You need instead to fetch your existing settings object, and only create a new one if that doesn't exist.

Your database will currently have several settings objects, one for each time you've loaded the view.