Should I release my subviews of UIView in the viewDidUnload when I have references to them as instance variables which retains them? I have build the GUI programmatically. I should do that right? Since both uiview and ivars retain then the objects would have 2 in retain-count, when view receives e.g. memory-warning then the UIView will release the subviews, but they still have +1 in retain count so I have to setself.myIvar = nil; In the viewDidUnload?
Thanks for your time.
You actually can release all retained subviews in viewDidUnload. But I used to do it in another way:
-(void) viewDidLoad {
someInstanceView1 = [[UIView alloc] init];
[self.view addSubview: someInstanceView1];
[someInstanceView1 release];
someInstanceView2 = [[UIView alloc] init];
[self.view addSubview: someInstanceView2];
[someInstanceView2 release];
//etc...
//you have a references to someInstanceView1 and someInstanceView2 with retained counts 1
}
In this case even if memory warning will arise, the view controller will remove all it's view subviews. And then call viewDidLoad again. So there would be no leaks and you don't need to care about releasing that ivars at all cause the only owner (it has the strong reference to the views) is the view controller's view and it will release them automatically.
Related
I dynamically add a subview to another uiview;
in the subview ,click a button to go back by the following method:
[self removeFromSuperView ];
but after manny times added subview and removed it,my app could crash ,the log said it was killed .
I found that calling [self removeFromSuperView] didn't release self. So what's the best methods to releas it?
If you are retaining the UIView on creation (or adding it to an array) the retain count will increase. For example:
// Retain count is 1
UIView *myView = [[UIView alloc] initWithFrame:myFrame];
// Retain count is 2
[myParentView addSubview:myView];
// Retain count is 1 again
[myView removeFromSuperView];
In the above example you can autorelease the view if it is immediately added as a subView or release it in your dealloc if it is an iVar.
EDIT: (other reasons your view could be retained)
// Retain count +1
[myArray addObject:myView];
// Retained in the setter created by the #synthesize directive
#property(nonatomic, retain) UIView *myView;
Anything else that states in the documentation that the property is retained.
You should also be careful of creating objects in the loadView method of a VC, if you do make sure you release them, as they will be created again when the loadView is called. This will happen if you VC's view is unloaded and then reloaded.
u should release at first. counterpart of "alloc" is "release", and counterpart of "addSubview" is "removeFromSuperView":keep those balance.
add view:
UIView *myView = [[UIView alloc] initWithFrame:myFrame];
[myParentView addSubview:myView];
[myView release];
remove view (the view will clear up in memory after removeFromSuperView):
[myView removeFromSuperView];
Looks like you are adding retained view as a subview. Its parent view retains it once again.
So when you cell [self removeFromSuperView]; it gets release message from superView, but still have to be releasd by creator.
My current understanding is that superviews have retains each of their subviews. For a subclass of a UIView, do I need to remove all of my subviews from their superview as part of dealloc? I'm currently just releasing my IBOutlets, removing observed notifications, and clearing up any pesky ivars.
Or is removing and releasing subviews part of a UIView's [super dealloc]?
As a part of the view's dealloc, the subviews are removed automatically. So you don't need to remove them. However, if your view has retained any of its subviews [aside from the automatic retain], you should release them during dealloc.
So for example suppose your view contained the following code:
[header file]
UILabel *myLabel;
#property (nonatomic, retain) UILabel *myLabel;
[implementation file]
someLabel = [[UILabel alloc]initWithFrame: someFrame];
[self addSubview: someLabel];
self.myLabel = someLabel;
[someLabel release]; // now retained twice, once by the property and once as a subview
someButton = [[UIButton alloc]initWithFrame: someOtherFrame];
[self addSubview: someButton];
[someButton release]; // retained once as it is a subview
then your dealloc method would look like this:
- (void) dealloc {
[myLabel release];
[super dealloc];
}
UIView retains its subviews, so it's responsible for releasing them. Your subclass doesn't own those views (unless you explicitly retain them), so you don't need to worry about releasing them.
So it sounds like you're doing the right thing.
I have created a view and assigned the view to viewcontroller
UIView *newView=[[UIView alloc] initWithFrame:CGRectMake(0,0,320,460)];
in viewDidLoad method I have assigned the view to the viewcontroller
-(void)viewDidLoad{
self.view=newView;
//[view release]; In this case also the application crashing
}
-(void)dealloc{
[newView release];//IN this case also the application crashing.
[super dealloc];
}
The crash log is this.
how to release the newView? or else the viewcontroller itself will take care of releasing the newView.
In most circumstances you will do the following:
- (void) loadView {
// Don't call super here if you assign the view property
UIView *newView = [[UIView alloc] initWithFrame: [UIScreen mainScreen].applicationFrame];
self.view = newView;
[newView release];
// the view is now owned and retained by the UIViewController
}
Apple recommends you allocate the view, assign and release it in -loadView and don't worry about it in -dealloc. This is important in cases when your view may be purged under low memory conditions.
I have a view which is slideshow settings, and another view which has a slideshow. Unfortunately, these views conflict because they are still in memory.
As far as I know, viewDidUnload and dealloc are only called in low-memory situations, and dealloc should not be called directly, so how do I completely remove a view. These views are within uinavigationcontrollers by the way.
If you've added a view with UINavigationController remove it with PopViewController.
Pseudocode:
UIView *newView = [[UIView alloc] init]; // retain = 1
[UINavigationController pushView: newView]; // retain = 2
[newView release]; //retain = 1
[UINavigationController popView]; //retain = 0, object will get destroyed
I am going over my code and trying to get a handle on proper memory management. This code:
imageView = [[[UIImageView alloc] initWithImage:myImage] autorelease];
Causes my application to crash. I am using multiple view controllers within a nav bar controller. The app works fine: I can select a person from the first view controller (tableview) and it puts me to a list of that persons photos, I can then select a photo from that view controller (tableview) and move to a final view with a scrollview for viewing the photo. Once I hit back on the navbar the previous view loads (list of photos in a tableview) however the app crashes right before the row is deselected using this code:
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if(RowSelected != nil)
{
[MainTableView deselectRowAtIndexPath:RowSelected animated:YES];
}
}
The selected row is stored when a the user clicks a row.
If I leave the code as:
imageView = [[UIImageView alloc] initWithImage:myImage];
The app runs fine. Am I doing something wrong? Do I not need to autorelease this?
Make sure you create that view in your view controller's -loadView or -viewDidLoad, not in its initializer. When the controller's view goes offscreen it usually gets released, which in turn releases its subviews; thus, you should not expect your reference to imageView to remain valid. If you for some reason need the image view to stay in memory even when the view controller's offscreen, then it's okay not to call -autorelease when you create it; just make sure to call [imageView release]; in your controller's -dealloc.
When you mark imageView for autorelease, it will be released the next time thru the run loop. If you still are referencing or using imageView somewhere then you are using a pointer to heap space that has been released. The heap space will get overwritten (sooner or later) and you will be referencing garbage and crash.
I think the correct solution is that imageView should be a property that is retained, but I'm not sure what you are doing with imageView so I'm only guesstimating here. If you add imageView to your view Controllers view it will retain it in the subviews array. Bottom line, it has to be retained by whoever is using it.
You would make imageView a retained property in the .h file:
#property (nonatomic, retain) UIImageView* imageView;
Then use the setter, which will retain it:
UIImageView* tmpIV = [[UIImageView alloc] initWithImage:myImage];
self.imageView = tmpIV; // copy the pointer, setter will retain it
[tmpIV release]; // release the original alloc
Don't forget the #synthesize to create the setter/getter.
The ImageView is in my .h. I am using this line it in my -viewDidLoad, i do not need the view once it goes offscreen:
imageView = [[[UIImageView alloc] initWithImage:myImage] autorelease];
I think that what i am doing is assigning the allocated UIImageView to my imageView and if i auto release then the retaincount will be off because my -dealloc releases? (corret me if im wrong)
if i check my -dealloc:
- (void)dealloc {
NSLog(#"%i", [photo retainCount]);
[photo release];
NSLog(#"%i", [imageView retainCount]);
[imageView release];
[super dealloc];
}
The retaincount of the imageView is 1 in NSLog, im guessing that when it goes to do [super dealloc] that it tries to take 1 more retain count off of the imageView when it is 0 already because of the [imageView release] ?
if i have the line: imageView = [[UIImageView alloc] initWithImage:myImage];
then the retain count is 2 in NSLog, 1 going into the [supper dealloc]
if i use kk6yb's method, then the app works no problems, however i think i shouldn't have to do it this way because using his way if i check my retain count in dealloc it is also 2 in the NSLog...
I am confused, i read alot about memory management yesterday to get a better grip on things, since i am releasing the imageView in the -dealloc i believe i do not need to autorelease on that line?
Is there a way to check memory leaks in xCode?
Thanks!