SKSpriteNode subclass: method to remove all joints

Question

I have created a subclass of SKSpriteNode. I connect instances of that class together with joints of type SKPhysicsJointLimit. I do this within my didEndContact(contact: SKPhysicsContact) in my GameScene:

var joint = SKPhysicsJointLimit.jointWithBodyA(contact.bodyA, bodyB: contact.bodyB, anchorA: pos1!, anchorB: pos2!)
self.physicsWorld.addJoint(joint)

This works well so far. Then i come to the point where i want to release the node from the joint. According to the SKPhysicsBody docs there is a property called "joints" which is an array holding SKPhysicsJoint objects. I thought thats exactly what I need, but I am not able to iterate over an instance's joints and remove them from the physicsWorld. To do the job i added a method to my custom SKSpriteNode subclass.

func freeJoints(world: SKPhysicsWorld){
        if let joints = self.physicsBody?.joints {
            for joint in joints{
                println("found a joint: \(joint)")
                // example print:
                //found a joint: <PKPhysicsJointRope: 0x7fbe39e95c50>
                world.removeJoint(joint as SKPhysicsJoint)
            }
        }
    }

Calling the method fails after the println() statement with the message "Swift dynamic cast failed". I would really appreciate your opinion in how to work with an SKPhysicsBody's joint property. More specifically: How to use (cast?) the items in the array to be able to remove them from a scene's SKPhysicsWorld.

Answer 1

I spent a little more time in investigating this. This is what I have come up with:

I decided to add an property to my SKSpriteNode subclass and manage the joints myself

    var joints: [SKPhysicsJointLimit]
override init(){
    ...
    self.joints = []
    ...
}

Everytime I add an joint to the scene's SKPHysicsWorld I also add it to the joints array of the SKNNode itself. Whilst iterating the SKPHysicsBody's joints-Array failed (see question) at the point I wanted to cast it to SKPhysicsJoint, removing items from the physics world works as intended when iterating the array of SKPhysicsJointLimit items:

func freeJoints(world: SKPhysicsWorld){
        for item in self.joints{
            println("removing item from physics world \(item)")
            world.removeJoint(item)
        }
        self.joints.removeAll(keepCapacity: false)
    }
}

This seems not to be the most elegant way to do the job, since there already is a framework managed array that promises to be same thing. But I was unable to utilize it and this works for now.