I'm using NSFetchedResultsController for my table view. I call -performFetch inside my controller's -viewDidLoad method.
Sometimes my controller gets unloaded and then re-loaded, resulting in another call to -viewDidLoad and -performFetch. I found that this was causing an error: "NSFetchedResultsController error: section '(null)' not found in controller". I found that calling -performFetch multiple times like this was causing the problem, and modified my -viewDidLoad: method to do the following:
if( fetchedResCtrlr.fetchedObjects == nil )
{
NSError *error;
if ( ![fetchedResCtrlr performFetch:&error] )
...
}
Being new to Core Data, I'm wondering if this is the correct action to take. Should I actually be able to call -performFetch: more than once without error? Should I be doing something in -viewDidUnload:?
Thanks!
Normally, there is nothing that needs to be done with the NSFetchedResultsController in the -viewDidUnload:. Also, checking for nil against the -fetchedObjects is normally not worth it. Sounds like your code has other flow issues. Calling -performFetch: more than once would only harm performance on its own, without any other ill effects.
Related
I am developing my first iPhone app for a couple of months and now I got stuck on a memory error “message sent to deallocated instance”. I have written down all my observations (from the debugger) but can't find the reason. I will really appreciate any help.
SITUATION:
I have created pick_ListBrowseController, a subclass of UITableViewController.
It is called to pick an item from a scrolling list. The objects presented come from a CareData database.
I useNSFetchedResultsController.
In the implementation of pick_ListBrowseController, there is a typical method returning a fetched results controller:
- (NSFetchedResultsController *) fetchedResultsController {
// If the fetched results controller already exists, return it:
if (fetchedResultsController != nil) { return fetchedResultsController;}
(…) // constructing fetchRequest object with entity and sort descriptors
[NSFetchedResultsController deleteCacheWithName:#"pick_List"];
// Create fetched request controller:
NSFetchedResultsController *aFetchedResultsController =
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:nil cacheName:#"pick_List"];
// Set the fetched results controller's delegate to self;
// it will send controllerDidChangeContent:
[aFetchedResultsController setDelegate: self];
// Assign this new fetched results controller to the property:
[self setFetchedResultsController: aFetchedResultsController];
// Return fetched request controller:
return fetchedResultsController;
}
BUG SCENARIO A:
STEP 1) I call my pick_ListBrowseController, select an item and navigate back. The view disappears.
In the debugger, I can see that the pick_ListBrowseController object had memory address 0x729b950
STEP 2) I call pick_ListBrowseController once again. It is now another instance, with memory address 0x755a4e0
STEP 3) When I try to pick an item, I get error message:
[pick_ListBrowseController controllerDidChangeContent:]: message sent
to deallocated instance 0x729b950.
The address is from STEP 1) ! For some reason, the framework code (which is not accessible for me) sends controllerDidChangeContent: to the already deallocated object from STEP 1), not to the object from STEP 2), as it should.
BUG SCENERIO B:
Even worse, it happens even when in STEP 1) I call a different controller object , also a subclass of UITableViewController. Steps 2) and 3) remain the same. The same bug occurs and in the debugger I can see that even now controllerDidChangeContent: is sent to the object from STEP 1). Hence it is sent not only to the wrong (and deallocated) object, it is even sent to an object from a different class!
QUESTIONS:
1) What may be the reason? How to fix it?
2) My app is really big. Is it possible that it became too big causing the memory problems described above? If yes, what can I do to get things right?
Currently, I use Xcode Version 4.2 build 4C199 and I use Automated Reference Counting (ARC) - I went through the refactor process “convert to Objective-C ARC”.
Any help will be highly appreciated.
It is likely that your FRC is not getting released when your VC is dealloc ed. If it is hanging around and has your VC as a reference to the delegate then you have a dangling pointer. Double check that you are cleaning up the FRC.
Just implementing my first delegate in objective-C. I thought I had everything in place however the call from my AddController back to ListController isn't being picked up in the ListController.
Given that I'm not getting an exception, and that I can see that the code does get to the point in the AddController where it calls the delegate, are there any fault finding tips?
So for example:
given the "delegate" call (see below) did not throw an exception can I assume that my delegate declarations in the same file are OK?
"[delegate newItemController:self didFinishWithSave:YES];"
given the parent controller so to speak does have the delegate specified in the *.h definition (see below), then this does implied I've correctly implemented the method in the *.m file, noting I get no build errors?
#interface RootViewController : UITableViewController {
is there a known way for delegate calls to go missing without an exception if certain items don't like up (i.e. if there is what should I check for)
thanks
Most common error I've seen for a delegate method not being called is a nil delegate property. In other words, forgetting to specify who the delegate is?
As for debugging tips, anytime I've seen a problem where a delegate is not being called is to set breakpoints throughout the code and step through the code. Then you can see where things are going and what is or isn't being called.
Also, you mention exceptions a lot. Objective C prefers not to use exceptions as they are a relatively expensive call in the language (unlike say Java). Objective C can and does use exceptions but they are rare. You might want to "beaf up" your understanding of error handling in objective c.
Have you set your delegate variable like this in your AddController:
self.delegate = <instance of ListViewController>
If it has not been set, then the delegate would be nil and the method call to the nil would result in nothing. Otherwise, delegate calls wouldn't really go missing like that.
I didn't understand your second point though.
I'm a c++ programmer new to objective-c.
I created a calculator app that is working fine using a single view. I have a Calculations class and a ViewController. Every time a button is pressed, an IBAction method in the ViewController calls methods defined in the Calculations class to handle the input and returns the output as an NSString which I then set as the value of the label.text field.
Now I am working on a tab bar app using the same Calculations class. This app has two tabs, each with a unique set of input buttons for the calculator (both views sharing the same input/output data). The first tab is identical to my first app with the single view, so I am trying to do this in a similar fashion.
Here is the problem:
When a button is pressed, the IBAction method that handles the input runs through the calls to the Calculations class methods (shown below) without error:
-(IBAction)readInput:(id)sender {
[_calculations input:[sender titleForState:UIControlStateNormal]];
inputField.text = [_calculations inputDisplay];
outputField.text = [_calculations outputDisplay];
}
however, both the inputDisplay and outputDisplay methods return nil. Using the debugger I noticed that I am unable to "step into" the calls to _calculations methods, instead the line is skipped and the value returned by both is nil. I added the following method:
-(IBAction)setNumber:(id)sender {
NSString *button =(NSString *)[sender titleForState:UIControlStateNormal];
inputField.text = button;
}
and if I attach this to the input buttons I can see the display updated. This seems to be an issue with calling the _calculations member functions and tab bar views (because this issue is not present using a single view).
I realize that I left out a lot of information, but I did it to avoid providing irrelevant information. I will provide all details that are necessary if asked.
Check to make sure _calculations is not nil.
You can send any message (call any method) on nil and it will just return nil, not cause an exception.
Without seeing more code it is going to be a bit difficult to diagnose.
If I was trying to debug this issue I would first make sure _calculations points to the object you want it to point to. If its loaded from a NIB then it might not be getting initialised, and still be nil. You can send messages to nil objects without any issues. If an object receives a message that it cant handle (the method doesn't exist, or the target object is nil) then the return for that call will be nil.
I have in the past put initilization code into the init: method, and spent a few hours why it wasn't being called, until it dawned on me that I needed to put my init code into the viewDidLoad:, or the initWithNibName:bundle: or even the initWithCoder: selector.
HTH, Matt
I Have the following code:
-(void) changeAnimation:(NSString*)name forTime:(int) times {
if(currentAnimation != #"attack")
{
id action = [CCAnimate actionWithAnimation:[self animationByName:name]];
id repeatAction = [CCRepeat actionWithAction:action times:times];
currentAction = [self runAction:repeatAction];
lastANimation = currentAnimation;
currentAnimation = name;
}
else if(currentAction.isDone)
{
//Here is where I would change the animation
//but I commented the code for now
}
}
So when I run this and click on the button that changes the animation to "attack" (by calling [mysprite changeAnimation:#"attack" forTime:1];), I get a EXC_BAD_ACCESS error from the "currentAction.isDone" line, the next time the function is called (the joystick will call changeAnimation to try and change the animation to "run" or "idle", but I want the attack animation to finish first). Any thoughts on whyI get this? currentAction is declared in my class.
Edit: there is nothing in the rest of the class that interacts with currentAction, beside a getter. Its declaration is in the .h (CCAction* surrentAction). Do I need to initialize it? I thought the returned value from runAction would be sufficient? ANyways, when I run the debugger, it is not nil, and assigned to the correct action.
Thanks,
Dave
Edit:
I ended up creating a sequence when "attacking" that calls a function that changes the currentAnimation, so i avoided the issue. Still no idea what was happening.
Here's the answer if your interested:
Other Post
More of the class is probably needed to really answer this properly, but the EXC_BAD_ACCESS typically happens because you're accessing something that has been released and is no longer available in memory.
I'm guessing that somewhere in your class you're releasing, either explicitly, or implicitly, the "currentAction" object asynchronously - and when you're checking later, it's done & gone and you're hitting this crasher.
In general, keeping a state variable or two that you always have known values on is a good way to go, and for the "actions" that you're going through, if they're asynchronous and doing their own memory management, leave them as such and work through some state variables that you maintain and control all the memory management around. It's a pretty reasonable pattern for asynchronous callbacks, either with the classic stuff or as you move into using blocks with iOS 4.0
I've created a program that uses core data and it works beautifully.
I've since attempted to move all my core data methods calls and fetch routines into a class that is self contained. My main program then instantiates that class and makes some basic method calls into that class, and the class then does all the core data stuff behind the scenes. What I'm running into, is that sometimes I'll find that when I grab a managed object from the context, I'll have a valid object, but its properties have been deallocated, and I'll cause a crash. I've played with the zombies and looked for memory leaks, and what I have gathered is it seems that the run loop is probably responsible for deallocating the memory, but I'm not sure.
Is there a way to determine if that memory has been deallocated and force the core data to get it back if I need to access it? My managedObjectContext never gets deallocated, and the fetchedResultsController never does, either.
I thought maybe I needed to use the [managedObjectContext refreshObject:mergeData:] method, or the [managedObjectContext setRetainsRegisteredObjects:] method. Although, I'm under the impression that last one may not be the best bet since it will be more memory intensive (from what I understand).
These errors only popped up when I moved the core data calls into another class file, and they are random when they show up.
Any insight would be appreciated.
-Ryan
Sounds to me like you are not retaining objects you want to keep hanging around. If you are doing something like this:
NSArray *array = [moc executeFetchRequest:request error:&error];
you do not own the returned array and it will most likely disappear when the current autorelease pool is drained. This will occur when the run loop finishes processing the current event.
All this is speculation. If you want a proper answer, you need to post your code.
It's hard to know what the problem is based on your description, but you might want to look at the Core Data memory management guide. You shouldn't have to worry about memory management for managed objects and their entities (they're fetched and faulted automatically). When you talk about "properties," do you mean custom properties backed by ivars? If so, these should be released in didTurnIntoFault and allocd as needed (probably in the accessor).
I was struggling with a similar issue. I'm using a managed object class and want to set its properties dependent on user input. But the sometimes the properties and sometimes the whole managed object were deallocated.
After reading the Apple documentation http://developer.apple.com/library/IOs/#documentation/Cocoa/Conceptual/CoreData/Articles/cdMemory.html the chapter "The Role of the Managed Object Context" I learned that managed objects are released each run loop completes.
And there is the golden advice to set
[myMangedObjectContext setRetainsRegisteredObjects:YES];
(I had to set it in the init method (initWithNibName for me) of my view controller.)
You should also regard to retain only the objects you need to as explained in the documentation. But read it yourself.
If I'm not right please correct me.
I also made a class that handles all my CoreData fetching and stuff. I ran into a couple of gotcha's, so here are some tips. (If I am making any memory management errors in these examples, please let me know.)
Two things:
1) Made a "fetchFiredObject" method in the CoreData handler class. So when I want to get a managedObject that has all its variables and is a "fully feathered bird" so to speak, instead of doing:
aManagedObject *myManagedObject = [myCoreDataHandler.managedObjectStorageArray objectAtIndex:1];
int x = myManagedObject.someVariable.intValue;
instead I do:
aManagedObject *myManagedObject = [myCoreDataHandler fetchFiredObjectAtIndex:1];
int x = myManagedObject.someVariable.intValue;
And in myCoreDataHandler's fetchFiredObjectAtIndex:i method, we're going into the array, finding the object key at index i, then doing a fetchRequest for that object key, and returning the freshly-fetched managedObject so that it won't have been faulted or deallocated, etc. :D
2) When I create a new child viewController, I populate its "myCoreDataHandler" value from the parent upon creation. However, this happens on a subsequent line of code after the line of code that creates the new viewController. Therefore, any code in the child's viewDidLoad that tries to use myCoreDataHandler's methods will return empty objects because viewDidLoad completes before the parent's next line of code where it sets the values of globals in the child object. So make sure you are not accessing your "Core Data handling object" from within viewDidLoad or anything local methods called by viewDidLoad! Instead call them from the parent after creating the new viewController.