SpriteKit - Run a method with two arguments after a random period of time - objective-c

Question

While trying to create a game for iOS I'm facing a problem: I cannot find a way to call a method that creates a SpriteKit node from another class that "calls itself" or repeats after a random period of time in an easy way.
The idea is this: I have a class where the scene is created. But then I have another class (subclass of SKSPriteNode) that creates the different SKSpriteNode that I need. I have one method called createObjectWithName: name position: position that takes two arguments (name and position). I need to call this method from my scene (fine until here), but I also need to repeat this method constantly in random periods of time. So, once it is called one time, it calls itself after a period of time, creating more SKSPriteNodes.
I've tried using performSelector and dispatch_after, but I hadn't had any luck so far.
Thank you in advance.

Answer 1

Unless I am missing something, I think you want to use SKAction for this solution.
You could have a method for starting the spawner like this :
-(void)startSpawner:(float)duration range:(float)range
{
SKAction *delay = [SKAction waitForduration:duration withRange:range];
SKAction *spawnBlock = [SKAction runBlock:^(void)
{
NSString *spawnName = #"name";
CGPoint *spawnPosition = CGPointMake(someX, someY);
SpriteNodeSubclass *node = [SpriteNodeSubclass createObjectWithName:spawnName andPosition:spawnPosition];
// do something with that node if you need to.
}];
SKAction *sequence = [SKAction sequence:#[delay, spawnBlock]];
SKAction *repeat = [SKAction repeatActionForever:sequence];
[self runAction:repeat];
}
I think it's ideal to use SKAction as opposed to dispatch_after, because if you pause SpriteKit, the SKAction will also pause.

Answer 2

You can store a timestamp property in your scene class (let's call it timeElapsedFromLastSpawn and initialize it with 0). Then you can use this property in your update method :
timeElapsedFromLast += timeElapsedFromLastUpdate;
if (timeElapsedFromLast > 5.0) {
[self spawnSpriteNode];
timeElapsedFromLast = 0;
}
This will spawn a new sprite every 5 seconds. (And you can randomize it easily)
I would also recommend for the spawning method to be not in a SKSpriteNode instance but outside (e.g. in the parenting scene/node class) as SKSpriteNode role is to represent a sprite and not being a factory of sprites (unless it creates child sprites for it to control directly)
EDIT:
To calculate timeElapsedFromLastUpdate you can use the following code (taken from Ray Wenderlich's site which has great tutorials about this stuff)
- (void)update:(NSTimeInterval)currentTime {
// Handle time delta.
// If we drop below 60fps, we still want everything to move the same distance.
CFTimeInterval timeSinceLast = currentTime - self.lastUpdateTimeInterval;
self.lastUpdateTimeInterval = currentTime;
if (timeSinceLast > 1) { // more than a second since last update
timeSinceLast = 1.0 / 60.0;
self.lastUpdateTimeInterval = currentTime;
}
[self updateWithTimeSinceLastUpdate:timeSinceLast];
}
you should implement updateWithTimeSinceLastUpdate method in your scene class or use the calculation directly in the update method above

Answer 3

If this is how you call the method from your scene:
[otherClass createObjectWithName:name position:position];
Then this is how you can use GCD to schedule that call for a random amount of time later:
dispatch_after(dispatch_time(
DISPATCH_TIME_NOW,
(int64_t)(arc4random_uniform((u_int32_t)(MAX_SECONDS * NSEC_PER_SEC)))),
dispatch_get_main_queue(),
^{
[otherClass createObjectWithName:name position:position];
});
(assuming MAX_SECONDS * NSEC_PER_SEC is small enough to be represented by a 32-bit quantity; otherwise look at piling two arc4random_uniform calls with suitable modulo arithmetic)
So a way to that in a repeating fashion, with a __weak safeguard to prevent arbitrary extension of the lifetime of your object could be to use a tail call:
- (void)scheduleNextObject
{
__weak YourClass *weakSelf = self;
dispatch_after(dispatch_time(
DISPATCH_TIME_NOW,
(int64_t)(arc4random_uniform((u_int32_t)(MAX_SECONDS * NSEC_PER_SEC)))),
dispatch_get_main_queue(),
^{
// weakSelf prevents self itself from being captured, so that self
// can be deallocated even with this loop ongoing. We'll explicitly
// check whether what was self still exists to stick with the idiom,
// though it's strictly unnecessary
YourClass *strongSelf = weakSelf;
if(!strongSelf) return;
[otherClass createObjectWithName:name position:position];
[strongSelf scheduleNextObject];
});
}