I programmatically create an ActivityIndicatorView with
UIActivityIndicatorView* cactivity = [[[UIActivityIndicatorView alloc]
initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite] retain];
Then when I want to stopAnimating and release in the next
- (void)connectionDidFinishLoading, im using an undeclared identifier? But i thought i retained it and had to release it myself.
First off there is no need to retain the UIActivityIndicatorView after you alloc init it, it already has an retain count of 1.
Just declare an UIActivityIndicatorView in the .h file, so you can then reference it as a Instance variable. (thnx Rob).
Local Declaration : You have declared the UIActivityIndicator in a local method due to which it is unreachable to other methods. You'll have to declare in the header file. Also, give it property of retain. Then, you can access it wherever you want.
No need of Retain Message : Also, when you have initialized it, its retain count is increased by 1, so no need to pass the retain message to it. You'll be having access to it anyways.
Undeclared identifier means the variable is not defined in the current scope. To have the same variable available in multiple methods, make it a class ivar or property.
Try to get to the result or avoid warnings using "autorelease". But this is not suppose to be good in every case.
Related
So I have the following code where I am releasing an object after pushing it to another view. When I analyse it I get the error - Incorrect decrement of the reference count of an object that is not owned at this point by the caller. Would anyone know how to fix this? I've tried so many options each time getting a different memory leak
- (void)showCurrentArticle:(id)sender {
if(animating)
return; //it is already there
animating = YES;
JsonViewController *newsController = [(JsonViewController *)[self.newsNavController.viewControllers objectAtIndex:0]retain];
newsNavController.title = #"Parliament";
Item *currentItem = (Item *)[self.fetchedObjectsArray objectAtIndex:currentItemIndex];
NSString * urlString = [CONST_FEED_DISCRIPTION_URL stringByAppendingString:currentItem.guid];
[newsController initWithURLString:urlString date:currentItem.date];
[self.navigationController pushViewController:newsController animated:YES];
[newsController release];
}
This code takes a view controller that's already present in the navigation stack, reinitialises it, then pushes it onto the stack again. This doesn't seem right at all. You probably should be creating a new view controller. What's the background on this? What are you trying to achieve?
You are popping, change a title, than you are doing an initialization...
Decide if you will do deep clone of JsonViewController (alloc, init, copy field values) or just reference copy (retain). It will be mess later if you try to mix.
Your retain and release of the newsController object are unnecessary. That is why you are getting the warning. It looks like newsController is owned by the newsNavController object, which will retain it. The only reason you would need to retain newsController in this code is if you needed to use it outside the scope of this method. Since you don't need to retain it, you don't need to release it, hence the error. You may be assuming that the -initWithURLString:date: method is incrementing the retain count, but it is only new, alloc, and retain that do this. You should probably rename that method to not use the term init to avoid confusion.
What are you doing with -initWithURLString:date:??? Are you just adding a url? Then you should call it addURL...... If you really initialize it again, you set the pointer of the newsController variable to a new object. The first object it pointed to gets lost -> leak.
I assume you named the init method wrong and just add a url to a controller, which is already in the stack and add it again with a higher retain count, but still the very same object.
Don't do this. Copy the object or better - create a new instance of the viewController!!!
This may sound a newbie question however I'm new to iOS dev.
I've following code in my project, the project is ARC enabled, and I get error on its execution (bad access), and would like to understand the cause of the problem and solve it.
on some button press following code is invoked in MTClassA.m file
-(void) someMethod
{
for (int i = 0; i < N; i++) {
...
(param1 and param2 are location variables)
...
mFlickr = [[MTFlickr alloc] initWithParam1:param1 param2:mparam2];
mFlickr.delegate = self;
[mFlickr fetchImages];
}
}
in MTClassA.h header file mFlickr is declared as MTFlickr* mFlickr so default it it with __strong qualifier.
the callback function of fetchImages class is following
- (void)didRecieveImageLinksFromFlickr:(NSArray*)response
param1:(NSString*)param1 param2:(NSString*)param2 {
...
}
So basically I would like to know is it correct to create mFlickr objects this way in for loop and expect the callback to work correctly, if no please suggest what need to be changed ?
P.S. Do I need to change mFlickr to local variable ? If yes how should I be guaranteed that param1 and param2 methods are the one's that I've passed for teach iteration in for loop ?
You are creating multiple instances of the mFlickr object within your loop, and presumably assigning them to the same instance variable. Under ARC an assignment to an instance variable will automatically release the previous value, so your mFlickr objects are getting destroyed as soon as they are created (except the last one).
Presumably your mFlickr object is setting itself as a delegate for a URL request, it is probably this callback which is failing since the request's delegate no longer exists.
If you are creating multiple instances you should store them in an array instance variable. The callback should include a reference to the particular instance that has returned, and at this point, you remove it from the array.
You don't need to change the mFLicker to local variable. The only thing that i found in your code wrong is that, you are immediately setting mFlicker to self after initializing it. i think you must want to set the delegate of the mFlicker that you can do it by
[mFlicker setDelegate:self]
Did you set #property for mFlicker?
.h
#property(nonatomic, retain) MTFlickr *mflicker;
.m
#synthesis mflicker;
I also had similar experience, ARC was releasing my object after initialization.
so try changing your code to
self.mFlickr = [[MTFlickr alloc] initWithParam1:param1 param2:mparam2];
mFlickr.delegate = self;
[mFlickr fetchImages];
I am also not sure but i just wanted to provide some help
I was just working on my application where I needed to set an instance variable of NSMutableData a value. Now I also created a property for my instance variable which means that my program automatically allocates it etc, right? But then I assigned it a value but it was not taking it but staying null. I then manually allocated it and then it suddenly accepted the value. So now my question is what is the need for properties and why do I have to manually allocate my instance variable although I have a property set up for it?
Thanks in advance!
edit: my code:
in my .h file I have
#interface FirstScreen : UIViewController{
NSMutableData* fetchedData;
}
#property(nonatomic, retain)NSMutableData*fetchedData;
in my .m file I have:
-(void) connectionDidFinishLoading:(NSURLConnection *)connection{
NSString* fetchedDataString= [[NSString alloc]initWithData:fetchedData encoding:NSUTF8StringEncoding];
}
Now if I do not implement:
-(void)viewDidLoad{
self.fetchedData=[[NSMUtableData alloc]init];
}
fetchedDataString does not have any value. However if it is allocated it has a value. I am confuces when to allocate instance variables and when not to.
It doesn't allocate. All properties do for you is define the instance variable & implement accessor methods.
I'm assuming by "assigning a value" you mean trying to set the contents of the NSMutableData object you thought had been allocated for you.
Now I also created a property for my instance variable which means
that my program automatically allocates it etc, right?
Wrong. If you synthesize accessors for the property, an ivar will also be created for it if you haven't created one. But your property is just a pointer... it doesn't point to anything until you create an object for it to point to, and set it:
self.fetchedData = [[NSMutableData alloc] init];
That's C. What you're saying is true for every single variable, whether it's local or an instance variable. It's one thing to declare storage for a variable (that's all you're doing by declaring a property). It's another to give it a value. This declaration in code:
NSMutableArray* arr;
...does not cause arr to take on any particular value (under ARC it's nil; prior to ARC it could be anything at all). It is certainly not an empty mutable array! But that's exactly analogous to what you're doing when you declare a property.
If this is the first value the variable is to adopt, that's called initializing. You might say in code:
NSMutableArray* arr = [NSMutableArray array];
But you can't do that in a property declaration, so you have to initialize at some later time while the code is running. A typical approach is to do this in your designated initializer, so that no matter what happens later there will be an actual array at this address, from very early on.
I've written a book on this topic (iOS programming), and the chapter dealing with the issue you're having is free to read online:
http://www.apeth.com/iOSBook/ch03.html
Do methods retain the arguments that are passed? If so, can I release these arguments in the next line? And if not, then when do I release these objects (in case I am allocating these locally)?
The language will not retain arguments automatically. However, code that obeys the rules will retain or copy anything that it needs to keep around after execution leaves its scope.
In other words:
id object = [[SomeClass alloc] init];
[otherObject doSomethingWithObject:object];
[object release];
This code should always be OK, because if doSomethingWithObject: needs to keep its argument around, it will send it retain, and if it doesn't, it won't.
No, they simply handle the object, they don't control the memory.
You should release something in the method it was created.
Or, if it's a property or an ivar, you should release it in the dealloc (if it is retained).
Methods do not increment the reference count. However if you assign it to a variable with retain count then you need to explicitly send a nil message to both. Release of a variable can be done when you no longer want to use it. So a allocated variable will have its reference count incremented whenever a retain message is sent to it. So you need to send equal number of release messages till reference count becomes zero.
I am trying to make a program that dynamically creates a button using the command:
[UIButton buttonWithType:UIButtonTypeRoundedRect]
But when I use these commands the delete the button I create:
[currentButton removeFromSuperview];
[currentButton dealloc];
[currentButton release];
I receive an error. How would I go about removing and deallocating the memory from a uibutton?
I got this problem long time ago, please notice that
[UIButton buttonWithType:UIButtonTypeRoundedRect]
has autorelease inside, so in your initialisation you need to do retain, like this:
_mybutton = [[UIButton buttonWithType:UIButtonTypeRoundedRect] retain];
and later point, you can do:
[_mybutton release];
Hope helps
:)
In the Objective-C/Cocoa framework, you encounter two different ways to receive objects: ones which you have explicitly allocated memory for (via a constructor) and ones that you have received memory reference to (via a class method).
FooBar *fone = [[FooBar alloc] initWithText:#"Hello, World!"];
In this example, memory is explicitly being allocated for the object by your call, using the alloc method, and then it is being initialized with data using the initWithText method that would have a method header like this:
- (id)initWithText:(NSString *)text;
On the other hand, you also will encounter objects that are created by classes automatically for you. An example of this would be below:
FooBar *ftwo = [FooBar fooBarWithWelcomeText];
In this example, a FooBar object is being returned even though we are not calling alloc to allocate memory for it. There are many different reasons to implement the method like this, but its mainly done to abstract certain details from the code that is using the object. The above example would have a corresponding method header like this:
+ (FooBar *)fooBarWithWelcomeText;
Depending on which approach is used, it changes how you interact with the memory of the object. So for the first example, after allocating the memory for the object you receive it back with a retain count of 1. If you are done using the object, you need to explictly release it with
[fone release];
In the second example, you are receiving an autoreleased object, which will be deallocated once the autoreleasepool is drained. If you want to keep it, you must explicitly retain with:
[ftwo retain];
If you do not wish to retain it, you can just leave it as is and it will be deallocated automatically. You can tell a method uses autorelease by two characteristics: 1) you will not utilize alloc when you receive the object; and 2) there will be a "+" next to the method heading. This means that the method is declared as a class method (similar to Java static methods).
So to finally answer your specific situation, you only need to make sure that the retain count is lowered to 1 (The only object having a reference to it was the autorelease pool). In your example, it would be done like this:
UIButton *currentButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[someView addSubView:currentButton];
// some code later
[currentButton removeFromSuperview];
You do not need the release statements because you never explicitly retained it. When you added the UIButton to another view, it retained the object so it incremented the reference count to 2. By removing it from the view, it is lowered back down to 1 so that when the autorelease pool is flushed, your UIButton will be deallocated. Btw, never call the dealloc method directly. When the retain count of an object is decremented to 0, the dealloc method will automatically be called.
You can't not dealloced the UIButton which you get through buttonWithType from system,if you don't alloced any instance then you are not entitled to call release on that.
In your case, you can use removeFromSuperview but not either dealloc or release .
You can't call dealloc directly on object, this is invoked by the system when you say release on object.
EDITED:
you could create you button using initWithFrame function of UIView. But you will get only the button type UIButtonTypeCustom which is by default, and also can't not change the button type because it's readonly property. So you would get the rounded button by using your some images.
You're not supposed to call dealloc directly. Try removing the dealloc line and see how that works.