Re: Method parameter is sometimes zeroed (weird problem)

FROM : Shawn Erickson
DATE : Mon Nov 19 18:15:29 2007

On Nov 19, 2007, at 8:58 AM, Stuart Crook wrote:

> Hi, I'm having a really weird problem, which is probably something 
> obvious...
>
> ObjectA is a subclass of NSObject and implements the method 
> (void)tabView:(NSTabView *)tabview didChangeHeightBy:(float)change, 
> which is a delegate method (of my own creation, not Cocoa's) for 
> ObjectB.
>
> ObjectB is a subclass of NSTabView, which holds ObjectA as its 
> delegate and invokes the delegate method on it with [[self delegate] 
> tabView: self didChangeHeightBy: change] where 'change' is a float 
> value.
>
> The problem is that in the delegate method, the 'change' parameter 
> is always 0.0. I've put in NSLogs, traced the values in debug and 
> passed in constant float values, and while a non-zero value is 
> always passed, the received parameter 'change' is always 0.0. BUT 
> only when called in this way. If I get ObjectA to call the method on 
> itself, the change parameter is passed correctly. The same is true 
> if I call the method from ObjectC, another NSObject subclass.
>
> This is under 10.4.11 on Intel. All objects are compiled from source 
> inside the same project.


Do you see any warnings emitted by the compiler about not knowing 
about that particular method? It sounds like the compiler is assuming 
you are passing an int (what the compiler assumes when it don't know 
about a method). This results in code pushing data into registers that 
the callee doesn't look at.

As a test try changing the definition to pass an int instead to see if 
the correct values start to show up.

-Shawn