Sprite kit rotation repeat - sprite-kit

Question

How do you make a sprite rock back and forth constantly like a boat?
Heres the code i wrote:
import UIKit
import SpriteKit
let boat = SKSpriteNode(imageNamed: "boat_floor")
var rotationVal = CGFloat(-1)
class GameScene: SKScene {
override func didMoveToView(view: SKView) {
backgroundColor = UIColor.whiteColor()
boat.size = CGSize(width: self.frame.size.width, height: self.frame.size.width)
boat.position = CGPoint(x: self.frame.size.width/2, y: 0)
boat.physicsBody = SKPhysicsBody(texture: SKTexture(imageNamed: "boat_floor"), size: boat.size)
boat.physicsBody?.dynamic = false
boat.alpha = 1
self.addChild(boat)
ChangeAngle()
NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: Selector("ChangeAngle"), userInfo: nil, repeats: true)
}
func ChangeAngle(){
let action = SKAction.rotateByAngle(rotationVal, duration:30)
if rotationVal < 0 {
rotationVal = CGFloat(M_PI)
boat.runAction(action)
}
else if rotationVal > 0 {
rotationVal = -CGFloat(M_PI)
boat.runAction(action)
}
print(rotationVal)
}
}

Answer 1

If I understand you correctly, you can do it like this (just copy&paste the code to see how it works):
import UIKit
import SpriteKit
let boat = SKSpriteNode(color: SKColor.greenColor(), size:CGSize(width: 200, height: 80))
class GameScene: SKScene {
override func didMoveToView(view: SKView) {
backgroundColor = UIColor.whiteColor()
boat.position = CGPoint(x: self.frame.size.width/2, y: 100)
boat.alpha = 1
self.addChild(boat)
let rotate = SKAction.rotateByAngle(-0.6, duration:4)
let sequence = SKAction.repeatActionForever(SKAction.sequence([rotate, rotate.reversedAction()]))
let complete = SKAction.sequence([SKAction.rotateByAngle(0.3, duration:2), sequence])
boat.runAction(complete, withKey:"someKey")
}
}
Using NSTimer is generally bad idea in SpriteKit because it don't respect node's, scene's or view's paused state.