I have an NSMutableArray defined in my AppDelegate class:
NSMutableArray *devices;
I populate the array from a class in the didFinishLaunchingWIthOptions method:
Devices *devs = [[Devices alloc] init];
self.devices = [devs getDevices];
The getDevices method parses a json string and creates a Device object, adding it to the array:
NSMutableArray *retDevices = [[NSMutableArray alloc] initWithCapacity:[jsonDevices count]];
for (NSDiectionary *s in jsonDevices) {
Device *newDevice = [[Device alloc] init];
device.deviceName = [s objectForKey:#"name"];
[retDevices addObject: newDevice];
}
return retDevices;
I then use the AppDelegate class's devices array to populate a tableView. As seen in the cellForRowAtIndexPath method:
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
Device *d = (Device *)[appDelegate.devices objectAtIndex:indexPath.row];
cell.label.text = d.deviceName;
When the tableview is populated initially, it works. But when I scroll through the list, and the cellForRowAtIndexPath is executed again, d.deviceName throws an error because it has gone out of scope.
Can anyone help me understand why? I'm sure it has something to do with an item being released... but... ??
Thanks in advance.
If it is indeed a problem with memory management, answering these questions should lead you to an answer:
Is deviceName declared as a retain or copy property by the Device interface declaration?
Is -deviceName synthesized? If not, how is it implemented?
Is devices declared as a retain property by the app delegate class's interface declaration?
Is devices synthesized? If not, how is it implemented?
Of course, it might not be a problem with memory management. It would help a lot if you were to provide the actual text of the error message and any provided backtrace.
Related
I know this is a relativly easy question, but I just can't figure out how to solve this problem:
One of my views will receive a dragOperation and the performDragOperation method should pass the NSURL to my AppDelegate which puts it in an mutArray...
The problem is, that I pass over a reference and the object disappears the moment performDragOperation is done. So I tried several things:
in performDragOperation:
//Puts the reference itself in the folderPaths Array
AppDelegate *appDelegate = [NSApp delegate];
[[appDelegate folderPaths] addObject:referenceTotheNSURLObject];
/* tried creating a NSString and putting it in too. Same result because local variables will disappear */
So I created a method in AppDelegate and tried different things:
- (void)addFilePath:(NSURL *)filePath {
NSURL *copyOfURL = [filePath copy];
[[self folderPaths] addObject:copyOfURL];
}
This makes the most sense to me and the only reason I can think about why this doesn't work is, because copyOfURL itself is a pointer and it points to an localObject that will disappear the moment the addFilePath method is finished? But I'm not allowed to use
NSURL copyOfURL = [filePath copy];
I also tried recreating an NSString object again. Same results.
- (void)addFilePath:(NSURL *)filePath {
NSString *pathString = [filePath absoluteString];
[[self folderPaths] addObject:pathString];
}
I know it will be some relatively simply solution but I'm stuck and can't figure it out. Thanks for your time!
According to the static analyzer if we have the following property:
#property (retain, nonatomic) SomeObject * object;
and then we assign the property like so:
self.object = [SomeObject alloc] init];
a leak occurs. This makes sense because the alloc init adds +1 to the retain count and then the retaining property also increments the retain count. What is the best solution here? typically I just add an autorelease like so:
self.object = [[SomeObject alloc] init] autorelease];
But sometimes this creates problems for me and I end up over releasing the object causing my app to crash. I don't have any specific examples right now but I remember I had to take out some autoreleases cause of the application crashing. Is there something I am missing here?
EDIT: I have a concrete example now of the issue I was running into.
NSMutableArray *newData = [NSMutableArray array];
//If this is true then we are showing all of the items in that level of hierarchy and do not need to show the summary button.
if (!(contextID.count >= 1 && [[contextID objectAtIndex:contextID.count - 1] isEqual:[NSNull null]]) && contextID.count != 0)
{
GeographyPickerItem * firstItem = [[GeographyPickerItem alloc] init];
firstItem.primaryString = [NSString stringWithString:#"Summary"];
firstItem.subString = [NSString stringWithString:#""];
firstItem.isSummaryItem = YES;
[newData addObject:firstItem];
[firstItem release]; //TODO: Figure out why this is causing EXC_BAD_ACCESS errors
}
self.hierData = newData;
The code above is in the init method of a viewcontroller. HierData is a retained property, which is released in the viewControllers dealloc method. GeographyPickerItem retains the two strings, primaryString and subString and releases them in its own dealloc method. My application crashes (sometimes) when the viewControllers are de-alloced following a pop off of a navigation controller. It crashes with a EXC_BAD_ACCESS signal in the dealloc method of GeographyPickerItem (either on [substring release] or [primaryString release]).
I don't understand why this is happening because I believe I am following proper memory management guidelines. If I comment out firstItem release everything is fine.
The autorelease method you mention is fine, as is the other common idiom of:
SomeObject *thing = [[SomeObject alloc] init];
self.object = thing;
[thing release];
If you end up overreleasing later on, that is your problem. This part, which you're apparently doing correctly, is not the problem.
SomeObject * new_object = [SomeObject alloc] init];
self.object = new_object;
[new_object release];
or use ARC
check the GeographyPickerItem, if the strings properties are assign (and change to retain), or check if you always initialize them (before release).
also remember the difference of manually allocating :
[[NSString alloc] initWith...]
You must release or autorelease.
[NSString stringWith...]
No need to release.
or use ARC like meggar said
Turns out the issue was simple, my dealloc method called super dealloc at the start of the method rather than at the end. You always have to release your instance variables before you call [super dealloc]!
Hi guys can somebody please advise how to cure the memory leaks in the code below
i've tried just about every combination of release and autorelease i can think of but every time either the app crashes or the leak remains
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
//get refereance to the textfield
UITextField *currentTextField = (UITextField*)[self.view viewWithTag:200];
//check which picker
if(pickerView.tag ==1)
{
// Only calls the following code if component "0" has changed.
if (component == 0) {
// Sets the global integer "component0Row" to the currently selected row of component "0"
component0Row = row;
// Loads the new values for the selector into a new array in order to reload the data.
newValues = [[NSMutableArray alloc] initWithArray:[pickerData objectForKey:[selectorKeys objectAtIndex:component0Row]]];
currentValues = newValues;
// Reloads the data of component "1".
[pickerView reloadComponent:1];
}
//run the selector logic
[self textFieldDidEndEditing:currentTextField];
}
hope someone can advise
many thanks
Your problem is these two lines:
newValues = [[NSMutableArray alloc] initWithArray:[pickerData objectForKey:[selectorKeys objectAtIndex:component0Row]]];
currentValues = newValues;
The first line allocated a new instance of NSMutableArray. The second line copies the pointer from newValues to currentValues, overwriting the pointer value in currentValues. Whatever currentValues was pointing to is lost. That's the leak.
You could fix it like this:
newValues = [[NSMutableArray alloc] init...
[currentValues release];
currentValues = newValues;
This way, whatever was pointed to by currentValues has its reference count decremented before you lose access to it.
You could also solve the problem by making currentValues an Objective-C property, and using the accessor methods via self.currentValues or [self setCurrentValues:]; those methods will handle retain/release for you.
Your NSMutableArray allocation is never released.
newValues = [[NSMutableArray alloc] initWithArray:[pickerData objectForKey:[selectorKeys objectAtIndex:component0Row]]];
You should autorelease that or release it later on when you know you don't need it anymore.
Not sure how you have currentValues defined, but this should work without leaks:
In your .h file:
#property (nonatomic, retain) NSArray * currentValues;
In your .m file:
#synthesize currentValues;
self.currentValues = newValues;
Please look at the code below and suggest the best approach. I can't quite tell whether the code is correct. When adding objects to arrays, do they get a retain count? In the second function, am I releasing the local variable "mySubview" or the original object?
// this is a class property
myArray = [[NSMutableArray alloc] init];
- (void)createSubview
{
UIView *mySubview = [[UIView alloc] init];
[self addSubview:mySubview];
[myArray addObject:mySubview];
}
-(void)eventHandler:(NSNotification *) notification
{
UIView *mySubview = [notification object];
[myArray removeObjectIdenticalTo:mySubview];
[mySubview removeFromSuperview];
[mySubview release];
}
When adding objects to arrays, do they
get a retain count?
Yes.
In the second function, am I releasing
the local variable "mySubview" or the
original object?
UIView *mySubview;' defines a local variable, mySubview, which is a pointer to -- a reference to -- an instance of the UIView class. There is no such thing as a "local object" or "stack object" in Objective-C (save for blocks, but that is beyond the scope of this question).
So, no, when you call [mySubview release] you are sending -release to the instance of of UIView included in notification.
That release is balancing the retain implied by the alloc. Which isn't the right pattern at all. You should do something like:
- (void)createSubview
{
UIView *mySubview = [[UIView alloc] init];
[self addSubview:mySubview];
[myArray addObject:mySubview];
[mySubview release];
}
-(void)eventHandler:(NSNotification *) notification
{
UIView *mySubview = [notification object];
[myArray removeObjectIdenticalTo:mySubview];
[mySubview removeFromSuperview];
}
Oh, by "class property", I'm assuming you mean "instance variable"?
I have seen a lot of talk about dynamic typing in objective-c. But i haven't seen any examples of what i think it is supposed to be.
lets say I have a generic function that is supposed to juggle two objects (one gets allocated and the other gets freed) and the calling object attaches it self to the newly alloced object. Both are inherited from class0
Please feel free to interpret this however you want if you think it will explain something!!
If the class is picked at runtime, how do i deal with the arguments list (? is a placeholder for now)
How do i alloc a object who's class is not defined until runtime?
-(void) juggle:(?*)objclass1:(?*)objclass2{
? temp = [? alloc] init];
objclass1 = temp;
[temp release];
[objclass2.view removefromsuperview];
[self.handle insertsubview:objclass1.view];
}
I have no idea what the code you have there is trying to do, it is not syntactically valid, and manipulating views has nothing to do with your questions. Anyway, if you really don't know the type you generally use "id" which is type cast to a "void *" for codegen. It has the special property that it is assumed to receive any message, so it does not trigger compiler warnings for unknown messages.
In order to instantiate a class you just need to be holding the "Class" object for it. In Objective C all instances of a class refer to a Class object (the isa pointer in the legacy runtime), which also responds to methods. So in other words, in the following code:
NSArray *myObject = [[NSArray alloc] init];
NSArray is actually an object. So this will generate equivalent code results:
Class myClass = [NSArray class];
NSArray *myObject = [[myClass alloc] init];
or even
Class myClass = NSClassFromString(#"NSArray");
NSArray *myObject = [[myClass alloc] init];
Which uses the function NSClassFromString which walks into the runtime and finds a class with the name you pass in.
All objects return their class if use the class getter, so to instantiate an object that is the same class as an existing object like this:
- (void) leakObjectWithSameClassAs:(id)object {
[[[object class] alloc] init];
}
This is what i have now
- (void)flipfromv1tov2:(UIViewController*)v1:(NSString*)nib1:(UIViewController*)v2{
if(v1 == nil)
{
UIViewController *newview = [[[v1 class] alloc] initWithNibName:nib1 bundle:nil];
v1 = newview;
[newview release];
}
[v2.view removeFromSuperview];
[self.view insertSubview:v1.view atIndex:0];
}
I cannot verify it yet because I have a linking problem...I added this func to my root controller but for some reason I get a warning that the function is implicitly declared. And the build fails because the function call never get linked to anything