How to Know when a Sprite Effect is Done - objective-c

Question

I am running a sprite effect in an SKScene at certain points. When the effect is not running I want to pause the scene as otherwise it takes up additional CPU even with no effect running. I was not able to find a delegate that tells me when the effect stops rendering so that I can pause the scene again. I could brute force it by having it wait a safe time, but is there a more elegant way to know when the effect is finished?
Setup in viewWillAppear:
self.skScene = [EffectsScene sceneWithSize:self.view.frame.size];
[self.skScene setBackgroundColor:[UIColor whiteColor]];
[self.skView presentScene:self.skScene];
[self.skView setPaused:YES];
Method that gets called to run the effect at a specific time:
-(void)deleteEffect
{
if (shouldRunDeleteEffect)
{
[self.skScene smokeEffectAtX:self.view.frame.size.width/2 andY:0];
[self.skView setPaused:NO];
shouldRunDeleteEffect = NO;
}
}
The actual scene details:
-(void)smokeEffectAtX:(float)x andY:(float)y
{
SKEmitterNode *emitter = [NSKeyedUnarchiver unarchiveObjectWithFile:[[NSBundle mainBundle] pathForResource:#"SmokeEffect" ofType:#"sks"]];
emitter.position = CGPointMake(x,y);
emitter.numParticlesToEmit = 1000;
[self addChild:emitter];
}

Answer 1

This method creates an SKEmitterNode, calculates how long the emitter will take to run based on its properties and the duration parameter, and adds an SKAction to the emitter to remove it from the scene after it is done running.
- (void) newSmokeNodeAtPosition:(CGPoint)position withDuration:(NSTimeInterval)duration
{
SKEmitterNode *emitter = [NSKeyedUnarchiver unarchiveObjectWithFile:[[NSBundle mainBundle] pathForResource:#"SmokeEffect" ofType:#"sks"]];
emitter.position = position;
// Calculate the number of particles we need to generate based on the duration
emitter.numParticlesToEmit = duration * emitter.particleBirthRate;
// Determine the total time needed to run this effect.
NSTimeInterval totalTime = duration + emitter.particleLifetime + emitter.particleLifetimeRange/2;
// Run action to remove the emitter from the scene
[emitter runAction:[SKAction sequence:#[[SKAction waitForDuration:totalTime],
[SKAction removeFromParent]]]
completion:^{
// Add code here to run when emitter is done
self.scene.paused = YES;
}];
[self addChild:emitter];
}