Question

I am getting a crash the second time I attempt to add a certain view as a subview. The crash happens here:

-(void)AddAsScrollableSubContext:(UIView*)view {
    [pExtendedScrollableSubContextBounds addSubview: view]; //CRASH HERE
    pSubScroll.userInteractionEnabled = true;
}

the second time I call…

[mSongContext AddAsScrollableSubContext:pEQRoot];

The flow is something along the lines of

[mSongContext AddAsScrollableSubContext:pEQRoot];
...Load a lot of stuff
...Press a Button
...Unload a lot of stuff
[pEQRoot removeFromSuperview];
...Press a Button
[mSongContext AddAsScrollableSubContext:pEQRoot];

When I get the bad access the callstack looks like the following:

Both objects (pExtendedScrollableSubContextBounds and pEQRoot) appear to be valid. Adding other subview to pExtendedScrollableSubContextBounds works fine and calling other operations on pEQRoot (subview, frame) also work.

I read the in objsend r0 was the object and r1 was the selector so I looked at the memory address for r1 and saw…

This feels like I am trashing memory somewhere around isKindOfClass: but I am not quite sure. Could anyone point me to more info on iOS obj_msgsend? is there a way I can setup a watch point to catch when this memory trash is occurring?

Answer 1

Use NSZombies to fix the problem.

On a slightly unrelated note, there’s a rule of thumb – NARC which stands for new, allocate, retain, copy. If a method call includes any of these keywords, then we have ownership of the object and we are then supposed to release the object.