Really weird error

My first thought is that the Planet objects have been deallocated. Run your program under Instruments using the zombies template.

isValid returning true doesn't contradict my theory. The behaviour of sending a message to a deallocated object is undefined.

isValid doesn't check if the timer is still allocated, it only checks if the timer is still capable of firing. This could be simply returning a BOOL ivar. That could be why your program doesn't crash at this point.

 

How did you do that? That NSLog code you posted above does not check whether the object exists.

 

A couple of thoughts:
When you say it crashes, what do you mean? Do you get a stack backtrace in the console output? Care to share?

Have you run it under the debugger, with a breakpoint on both the line within the for loop? You can re-write that code slightly to make debugging a little easier, something like:

Code:

for (Planet *aPlanet in planetArray) {
        NSTimer *makeShipTimer = [aPlanet.makeShipTimer]; // guessing on type
        [makeShipTimer invalidate];
}

You can set the breakpoint on the invalidate statement and see the result of the makeShipTimer call.

 

It also depends on what properties that the op declared in the header for the nstimer as well as if he is setting to nil anywhere after he invalidates the timer.