NSMutableDictionary throws a doesNotRecognizeSelector to objectForKey?

Question

I'm a total noob to iPhone programming, and I've run into an exception being thrown that I just can't wrap my head around.

Background: The error is happening in a custom subview, and occurs immediately upon loading the program. I'm getting an exception thrown in the overridden drawRect method. The code throwing the error follows:

- (void)drawRect:(CGRect)rect{
    NSNumber *points = [NSNumber numberWithInt: star.numberOfPoints];
    //HERE. Doesn't recognize selector?!
    CGPathRef t = (CGPathRef)[starPaths objectForKey:points];
 /*snip*/

starPaths is initialized in awakeFromNib as an NSMutableDictionary with capacity 1.

The exception that's getting thrown is -[NSObject doesNotRecognizeSelector:]

starPaths is declared in the header file for the view as

    NSMutableDictionary *starPaths;

and is initialized as

- (void)awakeFromNib{
    starPaths = [NSMutableDictionary dictionaryWithCapacity: 1];
}

Finally, I haven't been able to get to a point in the code where I successfully add elements to the dictionary, since the code to add an entry relies on receiving a nil response from the dictionary to know that the that specific entry needs to be built.

Any suggestions? Any other information I should provide? Any help at all would be appreciated, I feel like I'm missing something obvious, but I've been bashing my head against this all day with no luck.

Answer 1

If you do not retain the starPaths variable or explicitly allocate it yourself with [[NSMutableDictionary alloc] initWithCapacity:1] then it will be automatically released on the next iteration of the run loop.

You need to do

starPaths = [[NSMutableDictionary dictionaryWithCapacity:1] retain];

Or

starPaths = [[NSMutableDictionary alloc] initWithCapacity:1];

Just make sure to release it when you no longer need it.

Answer 2

A few things to check:

• Is starPaths declared as an NSMutableDictionary* instance variable? You mention that it is initialized. Did you use the dictionaryWithCapacity method (which returns an auto-release object) or initWithCapacity (which needs to be explicitly retained). To be safe, you may want to retain it and release it when done.

• Double-check to make sure the header files are properly included so the declaration of starPaths is included in implementation files that make use of it.

• Generally speaking if you're getting mystery errors it has to do with corrupted memory. Try putting a breakpoint on the first line of the drawRect method and do a "po starPaths" in the debugger console window to see what's in it and what type of object the runtime thinks it is.