Cocoa Object Idle Timer - objective-c

Question

I am trying to understand the best way to invalidate an object based on a specified idle time. I have a joystick object that when instantiated from the joystickAdded method below, automatically starts up an NSTimer for that instance:
Joystick
idleTimer = [NSTimer scheduledTimerWithTimeInterval:300 target:self selector:#selector(invalidate) userInfo:nil repeats:YES];
This works fine, but my joysticks array doesnt get cleaned up because the method that should be called when idle is joystickRemoved, but I have no idea how to call this, or if NSTimer is the best way for this.
JoystickController
void joystickAdded(void *inContext, IOReturn inResult, void *inSender, IOHIDDeviceRef device) {
JoystickController *self = (__bridge JoystickController*)inContext;
IOHIDDeviceOpen(device, kIOHIDOptionsTypeNone);
// Filter events for joystickAction
NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
[dict setObject:[NSNumber numberWithInt:kIOHIDElementTypeInput_Button] forKey:(NSString*)CFSTR(kIOHIDElementTypeKey)];
IOHIDDeviceSetInputValueMatching(device, (__bridge CFDictionaryRef)(dict));
// Register callback for action event to find the joystick easier
IOHIDDeviceRegisterInputValueCallback(device, joystickAction, (__bridge void*)self);
Joystick *js = [[Joystick alloc] initWithDevice:device];
[[self joysticks] addObject:js];
}
void joystickRemoved(void *inContext, IOReturn inResult, void *inSender, IOHIDDeviceRef device) {
// Find joystick
JoystickController *self = (__bridge JoystickController*)inContext;
Joystick *js = [self findJoystickByRef:device];
if(!js) {
NSLog(#"Warning: No joysticks to remove");
return;
}
[[self joysticks] removeObject:js];
[js invalidate];
}
void joystickAction(void *inContext, IOReturn inResult, void *inSender, IOHIDValueRef value) {
long buttonState;
// Find joystick
JoystickController *self = (__bridge JoystickController*)inContext;
IOHIDDeviceRef device = IOHIDQueueGetDevice((IOHIDQueueRef) inSender);
Joystick *js = [self findJoystickByRef:device];
// Get button state
buttonState = IOHIDValueGetIntegerValue(value);
switch (buttonState) {
// Button pressed
case 1: {
// Reset joystick idle timer
[[js idleTimer] setFireDate:[NSDate dateWithTimeIntervalSinceNow:300]];
break;
}
// Button released
case 0:
break;
}
}

Answer 1

You could use a delegate pattern.
1) Make a protocol JoystickDelegate, declare the method - (void)joystickInvalidated:(Joystick *)joystick.
2) JoystickController should then implement JoystickDelegate. Implement the method to remove joystick from your array.
3) Finally make a weak property called delegate in the Joystick interface and on every init of Joystick in joystickAdded assign self on js.delegate.
4) Now whenever invalidate is called, just call the delegate with self inside Joystick:
[self.delegate joystickInvalidated:self];