Ios – NSMergeConflict on iOS7

core-dataiosmergeobjective c

I have updated my app to support iOS 7 and have been faced with the problem that on one of screens in my [context save]; I get the following error:

NSCocoaErrorDomain Code=133020 "The operation couldn’t be completed. (Cocoa error 133020.)" UserInfo=0x1115a6d0 {conflictList=(
"NSMergeConflict (0x1115a670) for NSManagedObject (0xf25c850) with objectID '0xf25c070 <x-coredata://76AF57C8-F7FF-4880-B06B-63F8B780C96D/Screen/p7>' with oldVersion = 5 and newVersion = 6 
and old object snapshot = {\n    index = 3;\n    message = \"<null>\";\n    status = 0;\n} and new cached row = {\n    index = 3;\n    message = \"<null>\";\n    status = 0;\n}"

On iOS6 this problem does not occur.

Update:
Code for managedObjectContext

-(NSManagedObjectContext *)managedObjectContextForCurrentThread{
if ([NSThread isMainThread])
{
    NSManagedObjectContext *parentContext = self.mainManagedObjectContext.parentContext;
    [parentContext performBlockAndWait:^{
        NSMergePolicy *mergePolicy = [[NSMergePolicy alloc] initWithMergeType:NSMergeByPropertyObjectTrumpMergePolicyType];
        [[self mainManagedObjectContext] setMergePolicy:mergePolicy];
    }];
    return self.mainManagedObjectContext;
}
else
{
    NSMutableDictionary *threadDict = [[NSThread currentThread] threadDictionary];
    NSManagedObjectContext *threadContext = [threadDict objectForKey:kCGMManagedObjectContextKey];
    if (threadContext == nil)
    {
        threadContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        NSManagedObjectContext *parentContext = self.mainManagedObjectContext.parentContext;
        [parentContext performBlockAndWait:^{
            NSMergePolicy *mergePolicy = [[NSMergePolicy alloc] initWithMergeType:NSMergeByPropertyObjectTrumpMergePolicyType];
            [parentContext setMergePolicy:mergePolicy];
        }];
        [threadContext setParentContext:self.mainManagedObjectContext];
        [threadDict setObject:threadContext forKey:kCGMManagedObjectContextKey];
    }
    return threadContext;
}

}

Best Answer

I just spent two days debugging the exact same error. The difference between your app and mine is that mine only accesses core data from the main thread, so the merge error was even more puzzling.

In our case I narrowed it down to the fact that we had a unidirectional relationship - A has many Bs (modeled as an NSSet), but B doesn't know its A. We had a method that modified both an A and a B, and would cause a merge error when we went to save those changes. This code worked fine for a long time on both iOS 5 & 6, and only started to fail on iOS 7.

It's true that adding a merge policy will make the error go away, but it might also mask other errors. In our case we'd rather see those errors than risk having an inconsistent DB.

Changing the relationship to bidirectional made the error go away. The back links aren't necessary for our app, but they aren't hurting either. (And happily, changing this relationship was handled correctly as a lightweight migration - core data automatically filled in those back links for us.)

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in your apps plist file add a row call it "View controller-based status bar appearance" and set it to NO

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from http://www.openfl.org/developer/forums/general-discussion/iphone-5ios-7-cant-hide-status-bar/, mgiroux's solution

An example adding View Base Controller to your Info settings in Xcode

Ios – Explaining difference between automaticallyAdjustsScrollViewInsets, extendedLayoutIncludesOpaqueBars, edgesForExtendedLayout in iOS7

Starting in iOS7, the view controllers use full-screen layout by default. At the same time, you have more control over how it lays out its views, and that's done with those properties:

edgesForExtendedLayout

Basically, with this property you set which sides of your view can be extended to cover the whole screen. Imagine that you push a UIViewController into a UINavigationController. When the view of that view controller is laid out, it will start where the navigation bar ends, but this property will set which sides of the view (top, left, bottom, right) can be extended to fill the whole screen.

Let see it with an example:

UIViewController *viewController = [[UIViewController alloc] init];
viewController.view.backgroundColor = [UIColor redColor];
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Here you are not setting the value of edgesForExtendedLayout, therefore the default value is taken (UIRectEdgeAll), so the view extends its layout to fill the whole screen.

This is the result:

without edges for extended layout, the view fills the whole screen

As you can see, the red background extends behind the navigation bar and the status bar.

Now, you are going to set that value to UIRectEdgeNone, so you are telling the view controller to not extend the view to cover the screen:

UIViewController *viewController = [[UIViewController alloc] init];
viewController.view.backgroundColor = [UIColor redColor];
viewController.edgesForExtendedLayout = UIRectEdgeNone;
UINavigationController *mainNavigationController = [[UINavigationController alloc] initWithRootViewController:viewController];

And the result:

with edgesForExtendedLayout set, the view is just under the navigation

automaticallyAdjustsScrollViewInsets

This property is used when your view is a UIScrollView or similar, like a UITableView. You want your table to start where the navigation bar ends, because you wont see the whole content if not, but at the same time you want your table to cover the whole screen when scrolling. In that case, setting edgesForExtendedLayout to None won't work because your table will start scrolling where the navigation bar ends and it wont go behind it.

Here is where this property comes in handy, if you let the view controller automatically adjust the insets (setting this property to YES, also the default value) it will add insets to the top of the table, so the table will start where the navigation bar ends, but the scroll will cover the whole screen.

This is when is set to NO:

the table will scroll over the whole screen, but starts out partially covered

And YES (by default):

the table scrolls over the whole screen, and starts just under the navigation

In both cases, the table scrolls behind the navigation bar, but in the second case (YES), it will start from below the navigation bar.

extendedLayoutIncludesOpaqueBars

This value is just an addition to the previous ones. By default, this parameter is set to NO. If the status bar is opaque, the views won't be extended to include the status bar, even if you extend your view to cover it (edgesForExtendedLayout to UIRectEdgeAll).

If you set the value to YES, this will allow the view to go underneath the status bar again.

If something is not clear, write a comment and I'll answer it.

How does iOS know what UIScrollView to use?

iOS grabs the first subview in your ViewController's view, the one at index 0, and if it's a subclass of UIScrollView then applies the explained properties to it.

Of course, this means that UITableViewController works by default (since the UITableView is the first view).

Best Answer

Related Solutions

Objective-c – Cannot hide status bar in iOS7

Ios – Explaining difference between automaticallyAdjustsScrollViewInsets, extendedLayoutIncludesOpaqueBars, edgesForExtendedLayout in iOS7

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