Problem with removing a subview and then adding it again - iphone

Question

I have a problem with removing a subview, or more precisely with checking if it is still there after having deleted it.
My app first adds a subview to self.view.
[self.view addSubview:tabsClippedView];
Then it adds another subview to this subview (to which it adds several buttons as subviews, but I guess this is unimportant in this context):
[tabsClippedView addSubview:tabsView];
Finally, I have a method which allows the tabsView to be deleted and then created again. I need to do this so as to update the number of buttons in that tabsView (as the user can delete buttons). The method looks basically like this:
[self.tabsView removeFromSuperview];
After that I call a method called showTabs (which I already called in the very beginning of the app in order to add the subViews). This is where it all becomes problematic and where my app crashes (I get no error in the debug console, so I don't really know what the issue is...):
if ([tabsClippedView isDescendantOfView:self.view]) {
NSLog(#"There is already a tabsClippedView.");
} else {
NSLog(#"There is no tabsClippedView. I'll add one...");
[self initTabsClippedView];
}
This is where the app crashes: when trying to assess if tabsView isDescendantOfView (I don't get any of the following logs):
if ([tabsView isDescendantOfView:tabsClippedView]) {
NSLog(#"There is already a tabsView");
} else {
NSLog(#"There is no tabsView for the buttons. I'll add one including buttons.");
[self initTabs];
}
I'd be grateful for any suggestions where the problem could be.
EDIT:
These are the methods to set up my views:
-(void) initTabsClippedView { // sets up tabsClippedView
NSLog(#"initTabsClippedView method started...");
CGRect tabsClippedFrame = CGRectMake(258,30,70,81*6);
tabsClippedView = [[[UIView alloc] initWithFrame:tabsClippedFrame] autorelease];
tabsClippedView.clipsToBounds = true;
[self.view addSubview:tabsClippedView];
NSLog(#"initTabsClippedView method ended.");
}
-(void) initTabs {
NSLog(#"initTabs started. Adding buttons to tabsClippedView...");
CGRect tabsFrame = CGRectMake(-30,0,50,480);
tabsView = [[[UIView alloc] initWithFrame:tabsFrame] autorelease];
[tabsClippedView addSubview:tabsView];
// sets up buttons in tabsClippedView
And this is where I delete the tabsClippedView (triggered by a button found in tabsClippedView):
-(void)tabDelete:(id)sender
{
UIButton *button = (UIButton *)sender;
[UIView animateWithDuration:0.75
delay:0
options:UIViewAnimationOptionCurveEaseIn
animations:^{
button.transform = CGAffineTransformMakeTranslation(-30, 0);
}
completion:^(BOOL finished){
[UIView animateWithDuration:0
delay:0
options:UIViewAnimationOptionCurveEaseIn
animations:^{
[self.tabsView removeFromSuperview];
//...
}
completion:^(BOOL finished){
NSLog(#"tabsView removed from Superview. Objects Deleted.");
[self showTabs];
NSLog(#"TabDelete finished. Button removed and tabsView updated accordingly.");
}
];
}];
And this is the showTabs method which was already called when I started the app:
-(void)showTabs {
NSLog(#"showTabs started...");
currentView = #"Tabs";
if ([tabsClippedView isDescendantOfView:self.view]) {
NSLog(#"There is already a tabsClippedView.");
} else {
NSLog(#"There is no tabsClippedView. I'll add one...");
[self initTabsClippedView];
}
if ([tabsView isDescendantOfView:tabsClippedView]) {
NSLog(#"There is already a tabsView");
} else {
NSLog(#"There is no tabsView for the buttons. I'll add one including buttons.");
[self initTabs];
}

Answer 1

Is it possible that you are getting EXC_BAD_ACCESS? Is it possible that the app is crashing because tabsView is deallocated when you send isDescendantOfView: to it. If you run with breakpoints enabled it should tell you the reason for the crash. If it is an EXC_BAD_ACCESS problem you should try NSZombie.
To activate NSZombie do the following:
Get info of the executable.
Go to the arguments tab.
In the "Variables to be set in the environment:" section add:
Name: NSZombieEnabled
Value: YES
Then run your app as usual and when it crashes it should tell you which deallocated object received what message.
EDIT: Just saw your edit. I think I nailed it. You're autoreleasing the views when you create them, so when they are removed from their superviews they are no longer retained and thus deallocated. You're app crashes because you're trying to run methods on deallocated views.
EDIT 2: Thought I should tell you that there is a better solution than the one posted by Praveen S.
Change your code as follows:
[tabsClippedView release];
tabsClippedView = [[UIView alloc] initWithFrame:tabsClippedFrame];
and
[tabsView release];
tabsView = [[UIView alloc] initWithFrame:tabsFrame];
The above code does the same thing as the code posted by Praveen S, but without the autorelease. An autorelease is more expensive than a regular release and should only be used when needed and in this case it isn't.
Rather than releasing before you allocate a new view you probably want to release the view when you're done with it:
[tabsView removeFromSuperview];
[tabsView release];
tabsView = nil;
or simply
[tabsView removeFromSuperview];
self.tabsView = nil;
and then instead of:
if ([tabsView isDescendantOfView:tabsClippedView]) ...
you can use:
if (tabsView) ...
As you might have noticed, there really is no need for you to retain the view. You could just as well do the following:
tabsView = [[UIView alloc] initWithFrame:tabsFrame];
[tabsClippedView addSubview:tabsView]; // This retains tabsView
[tabsView release];
and then to remove the view you would use:
[tabsView removeFromSuperview]; // This will release the tabsView
tabsView = nil;
Also remember to set the views to nil in viewDidUnload.
EDIT 3: Why self made such a difference:
What you need to understand is how properties and reference counting works. There are books and such you could read about it. I'm sure Google can provide you with some good references as well.
The difference between
self.tabsView = [[UIView alloc] initWithFrame:frame];
and
tabsView = [[UIView alloc] initWithFrame:frame];
is that self.tabsView is accessing the properties setter, while tabsView is accessing the instance variable directly.
A nonatomic, retain property's implementation looks something like the following:
- (void)setTabsView:(UIView *)view
{
if (view != tabsView) {
[tabsView release];
tabsView = [view retain];
}
}
So the property is taking care of the memory management for you. In my solution I take care of the memory management myself and thus I don't need the property to do it for me, so I don't use it.
I hope this explains why self made such a difference.

Answer 2

Change your code as follows:
self.tabsClippedView = [[[UIView alloc] initWithFrame:tabsClippedFrame] autorelease];
and
self.tabsView = [[[UIView alloc] initWithFrame:tabsFrame] autorelease];