Ken Thomases wrote:
On Mar 23, 2008, at 8:18 PM, Tron Thomas wrote:
At this point, the compiler only knows that object is an id. It
doesn't know the specific class. So, of any of the "value" methods it
might know about, it doesn't know which specific one is meant.
Normally that wouldn't matter, but when you're dealing with float
returns (or struct returns) the generated code would be different.
In other words, the compiler is generating the code here as though it
were invoking a "value" method that returns an int. What is actually
being invoked is a method which returns a float. The mismatch causes
the problem.
The problem is even though the value is updated to some non-zero
value, the observed value is always zero. I have tried stepping
through the code and verified that when I step into [AnotherObject
value] method from the call in [SomeObject
observeValueForKeyPath:ofObject:change:context:], the _value instance
member is non-zero. Yet when I return to the calling method, the
local value variable gets set to zero. This does not make sense.
What would allow the SomeObject instance to get the proper value for
AnotherObject when observing it?
There are two approaches to fixing this:
1) Use a method name which won't be ambiguous about its return type,
such as floatValue. It's not the name that actually matters, it's
that all of the "floatValue" methods that the compiler might know
about at that point have a return type of float -- because what
perverse soul would create a floatValue method that returned something
other than float -- so there's no chance of confusion.
2) Cast "object" to the specific class that you know it to be (i.e.
AnotherObject*). You would have to make sure you've imported
AnotherObject.h, of course.
Cheers,
Ken
Using a type cast solved the problem. Thanks Ken.
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