R – Overreleasing here

memory-managementobjective c

I have been getting EXC_BAD_ACCESS on some devices in ad hoc beta for my app see here:
Help debugging iPhone app – EXC_BAD_ACCESS

I have managed to use atos -arch armv6 -o myapp.app/myapp 0x000037a6
in terminal to track down the method that's causing this problem, and it's lead me to this piece of code:

for (UIView *view in scrollView.subviews) {
    [view removeFromSuperview];
}

I suspect that the app is receiving a memory access warning, and releasing the scrollview or UIImageViews which are it's children, so when I use that method above, it hits an error (and a crash), since it's overreleasing a view.

My question is, how can I make this safe, so that it's only released if it hasn't yet been released?

Best Answer

You are modifying an array while you iterate over it. It's subtle, but because removeFromSuperview removes it from the list of subviews, you are changing the array. Change your code to this,

NSArray *subviews = [scrollView.subviews copy];
for (UIView *view in subviews) {
    [view removeFromSuperview];
}
[subviews release];

and you should be fine.

Related Solutions

R – View being released when in use due to memory warnings

Is PictureView retained in your controller (I'm assuming it's a subview of your controller's view)? If it's not retained, then you've got a dangling reference. When your view controller is not frontmost, and it receives a -didReceiveMemoryWarning message, by default it will release its view member. If you have pointers into subviews of that, and they're not retained, you'll end up in this situation.

The first thing to try is overriding -didReceiveMemoryWarning and calling clearPage:

- (void) didReceiveMemoryWarning {
    [myPictureView clearPage];
    myPictureView = nil;
    [super didReceiveMemoryWarning];
}

Objective-c – Release in viewDidUnload and dealloc both

Unless you need to break a retain cycle, you should generally only be releasing objects in your dealloc method. viewDidUnload is an exception; it is invoked in low memory situations and should be used to release anything that you can.

If you do need to release them anywhere else, then always set the reference to nil after the release. That'll protect your app from blowing up later (likely in dealloc).

Note that the documentation quite explicitly calls out that the view property will already be nil when viewDidUnload is called.

Best Answer

Related Solutions

R – View being released when in use due to memory warnings

Objective-c – Release in viewDidUnload and dealloc both

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