I have some confusion using NSMapTable.
I have NSMapTable with NSPointerFunctionsWeakMemory:
_controllersTable = [[NSMapTable alloc] initWithKeyOptions:NSPointerFunctionsWeakMemory|NSPointerFunctionsObjectPointerPersonality
valueOptions:NSPointerFunctionsWeakMemory|NSPointerFunctionsObjectPointerPersonality
capacity:0];
Assume I create UIViewController and add it to MapTable:
MyVC *myVC = [[MyVC alloc] init];
[self.controllersTable setObject:#1 forKey:controller]
MyVC.m
- (void)dealloc {
// [[[controllersTable keyEnumerator] allObjects] count]] == 0
}
So, by the time MyVC calls dealloc, there is not entry for that VC. Are there any way to get value from NSMapTable in that case?
PS
I can't use NSPointerFunctionsStrongMemory for storing keys, because it can introduce retain cycle.
Related
This is my code
__weak KDObject *obj = [KDObject fetchObj] ;
NSLog(#"%#", obj) ; // I think it should be nil, but it is not
obj.i = 10 ;
NSLog(#"%d", obj.i) ;
In KDObject.m
#implementation KDObject
+ (instancetype)fetchObj
{
return [[self alloc] init] ;
}
#end
the result is the same whatever KDOjbect.m is compile with -fno-objc-arc flag or without -fno-objc-arc flag
Anybody has ideas why obj is not nil ?
Related to your Q and to your answer:
-fectchObject is a method not belonging to any method family with ownership transfer. Therefore ARC has to ensure that returning the reference is safe. That means that losing the strong reference in the local scope of -fetchObject does not give up the last reference.
One way to accomplish this is to use the autorelease pool. But ARC does not guarantee that the ARP is used. Moreover it tries not to use the ARP, because it is the solution with the highest memory pressure.
So the things happening depends of the compiler implementation, attributes set to the method and what the compiler sees in source code (esp. implementation of -fetchObject). So you should not rely on returning in ARP.
__weak is guaranteed to be nil, if the object is destroyed. But it is not guaranteed that the object is destroyed in the earliest possible moment. This is subject of optimization.
From the docs about __weak
__weak specifies a reference that does not keep the referenced object alive. A weak reference is set to nil when there are no strong
references to the object.
Whether it's __weak or not KDObject *o = [[KDObject alloc] init] creates an object so o is not nil.
__weak is something realated to memory management. If none of strong objects are pointing to a weak object, it would be released from memory.
- (void)loadView
{
[super loadView];
TestObject *obj_ = [[TestObject alloc] init];
pObj = obj_;
if(pObj == nil)
{
NSLog(#"pObj_ is not nil");
}
__weak TestObject *obj2_ = [[TestObject alloc] init];
if(obj2_ == nil)
{
NSLog(#"obj2_ is nil");
}
__weak TestObject *obj3_ = [TestObject createInstance];
if(obj3_ == nil)
{
NSLog(#"obj3_ is nil");
}
}
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
if(pObj == nil)
{
NSLog(#"pObj is nil");
}
}
KudoCC requested this code. I used LLVM5.1. If I use -fno-objc-arc to TestObject.h, the objc3_ became not nil.
Assuming that a view controller is created like this:
#property (nonatomic, strong) SomeViewController *someViewController;
...
self.someViewController = [[SomeViewController alloc] initWithView:imgView];
[self addChildViewController:self.someViewController];
self.someViewController.view.frame = self.view.bounds;
[self.mainView addSubview:self.someViewController.view];
Why would it not get released by the following?
__weak MainViewController *weakSelf = self;
self.someViewController.didCloseBlock = ^{
[weakSelf.someViewController.view removeFromSuperview];
[weakSelf.someViewController willMoveToParentViewController:nil];
[weakSelf.someViewController removeFromParentViewController];
weakSelf.someViewController = nil;
};
I can tell it's not getting released because if I keep opening and closing the view controller (creating a new instance each time I open one), it causes low memory warnings (and then a crash on iOS5), and in SomeViewController didReceiveMemoryWarning, I see a log for the number of times I've created a new SomeViewController. For example, when I get the memory warning after opening 9 new SomeViewControllers, I will get 9 didReceiveMemoryWarning logs, indicating that I have 9 SomeViewController instances in memory, even though I'm nilling each one out in the code above.
You're retaining your view once in your property with the strong annotation and again with self.someViewController = [[SomeViewController alloc] initWithView:imgView];
Using the synthesized variable should get rid of this:
_someViewController = [[SomeViewController alloc] initWithView:imgView];
If you're not using ARC, you can use self.someViewController = [[[SomeViewController alloc] initWithView:imgView] autorelease];
I'd probably go for the first option, ARC or not though.
You are just setting the block didCloseBlock, nothing else actually. Do you execute it?
I have a project I am working on, to learn some more about JSON and restkit. It all is working great, however I am having trouble with an array losing it's values.
This is the last method that is executed in my network request.
SHRetrieveStoresWS.m
- (void)objectLoader:(RKObjectLoader *)objectLoader didLoadObjects:(NSArray *)objects
{
self.stores = [[NSArray alloc] initWithArray:objects];
StoresViewController *viewController = [[StoresViewController alloc] init];
[viewController didLoadObjects:objects];
for (Store *aStore in stores) {
NSLog(#"%#", [aStore longName]);
}
}
Which calls this method in my view controller.
StoresViewController.m
#property (strong, nonatomic) NSArray *data;
- (void)didLoadObjects:(NSArray *)aArray
{
NSLog(#"%d", aArray.count);
self.data = [[NSArray alloc] initWithArray:aArray];
NSLog(#"%d", data.count);
[self.tableView reloadData];
}
The values are correct when I ask for the values within this method, but the array shows 0 objects immediately afterwards. Am I missing something here?
I am later checking the value with this method.
- (IBAction)pushMe:(id)sender
{
NSLog(#"Data: %d", self.data.count);
}
You should pass the data in the segue...
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if ([segue.identifier isEqualToString: #"MY_IDENTIFIER"]){
StoresViewController *viewController = segue.destinationViewController;
[viewController didLoadObjects: objects];
}
}
That should work for you! Just change MY_IDENTIFIER to whatever the identifier of your segue is.
StoresViewController is initialised as a local variable which is only accessible in the method that it was declared (aka objectLoader). After objectLoader has completed, the local variable is no longer valid.
The problem is most likely that you're creating multiple instances of StoresViewController instead of giving your network controller a reference to the original instance.
You can demonstrate it to yourself by printing out self in -viewDidLoad and again in didLoadObjects:. You'll see that the pointer addresses are different.
This line is the culprit:
StoresViewController *viewController = [[StoresViewController alloc] init];
Instead of instantiating StoresViewController again, add a property to your SHRetrieveStoresWS class and use it to hold a reference to your view controller.
#property (strong) StoresViewController *viewController;
You'll need to set that property before -didLoadObjects: is invoked.
I am using "LIExposeController" to create new UIViewControllers. This brings up some memory warnings that I am not able to fix.
- (UIViewController *)newViewControllerForExposeController:(LIExposeController *)exposeController {
UIViewController *viewcontroller = [[[MyViewController alloc] init] autorelease];
return viewcontroller; // warning here saying object with a + 0 retain count returned to caller where a + 1 (owning) retain count is expected
}
- (void)shouldAddViewControllerForExposeController:(LIExposeController *)exposeController {
[exposeController addNewViewController:[self newViewControllerForExposeController:exposeController]
animated:YES];
} // warning here saying potential leak of an object
LIExposeController *exposeController = [[[LIExposeController alloc] init] autorelease];
exposeController.viewControllers = [NSMutableArray arrayWithObjects:
[self newViewControllerForExposeController:exposeController],
nil]; // warning here saying potential leak of an object
A method starting with new is expected to produce an object with retain count +1 and not an autoreleased/retain count +0 object. ARC and the Static Analyzer both follow these conventions as rules, and you should fix your code to meet them or rename your method to not clash with the conventions.
I must have misunderstood some of the memory management rules, because when I try to fix a memory leak, the App crashes. Let me show you some code:
calendarRequestLog is a property of type MutableDictionary in a singleton object, that exists as long as the App runs. Here's the declaration in the .h file:
#property (nonatomic, retain, readonly) NSMutableDictionary *calendarRequestLog;
I allocate it with (in init):
calendarRequestLog = [[NSMutableDictionary alloc] init];
I fill it with this (notice the retain, that creates the memory leak):
[calendarRequestLog setObject:[[NSMutableArray arrayWithObject:delegate] retain] forKey:date];
I sometimes access it with this:
NSMutableArray* delegates = [calendarRequestLog objectForKey:date];
if(delegates != nil) {
// add delegates
}
I empty it with this:
NSMutableArray* delegates = [calendarRequestLog objectForKey:date];
if(delegates != nil) {
for (id <ServerCallDelegate> delegate in delegates) { … }
// clear the request from the log
[calendarRequestLog removeObjectForKey:date];
}
Here's the code that crashes when I remove the retain above:
NSMutableArray* delegates = [calendarRequestLog objectForKey:date];
if(delegates != nil) {
if([delegates containsObject:delegate]) // crash
[delegates removeObject:delegate];
}
It crashes because delegates is deallocated but not nil. To be more precise, I get an EXC_BAD_ACCESS Exception.
All these methods may be called in different orders or multiple times.
I cannot figure out, why this happens. I thought, collections are supposed to retain their objects - as this array-object (delegates) is still in the collection, it should not be deallocated. Other code cannot be responsible, I showed you all occurrences of calendarRequestLog.
I appreciate all the help I can get!
#Edit
I think I got it.
I call the crashing method when the delegate gets deallocated, so that I do not call the delegate per accident later.
But: I retain the delegates in my calendarRequestLog, so it cannot get deallocated as long as this doesn't get called:
// clear the request from the log
[calendarRequestLog removeObjectForKey:date];
...which in turn, deallocates the delegate and calls the crashing method. As the calendarRequestLog has removed the delegates, but not yet the key, we crash.
Ok, I will solve this differently. Thanks for all the comments - thanks to you, I looked elsewhere!
Did you try retaining when fetching so nobody releases your object while you're using it?
NSMutableArray* delegates = [[calendarRequestLog objectForKey:date] retain];
if(delegates != nil) {
if([delegates containsObject:delegate]) // crash
[delegates removeObject:delegate];
}
[delegates release];
Common practice is the following, because you already retain in the .h file:
//create local instance, then copy that to the class wide var
NSMutableDictionary *_calendarRequestLog = [NSMutableDictionary alloc] init];
self.calendarRequestLog = _calendarRequestLog;
[_calendarRequestLog release];
Also, I don't really understand why you would retain here:
[calendarRequestLog setObject:[[NSMutableArray arrayWithObject:delegate] retain] forKey:date];
Why not just change that to:
[calendarRequestLog setObject:[NSMutableArray arrayWithObject:delegate] forKey:date];
Write instead
calendarRequestLog = [[NSMutableDictionary alloc] init];
this
self.calendarRequestLog = [NSMutableDictionary dictionary];
and try to use property instead ivar