CODEWITHSUNDEEP
iosiphonexcodeswiftios8
ganjan
ganjan

Reputation: 7616

Swift: SKNode should have optional types, Optional member does not have member

I had a working and compiling Swift game before I updated to the new XCode and suddenly a lot of errors has appeared. Here is two I haven't been able to fix. 

func centerOnNode(node: SKNode ) {

   let cameraPositionInScene = node.scene?.convertPoint(node.position, fromNode: node.parent!)

   var y = CGFloat(node.parent?.position.y - cameraPositionInScene?.y!)            
   // ERROR:
   // Operand of postfix ‘!’ should have optional types; Type is CGFLoat

   let x = CGFloat(node.parent.position.x - cameraPositionInScene.x)
   // ERROR: 
   // SKNode? does not have a member position

   // push the camera a bit up
   y -= 75

   node.parent.position = CGPointMake(x, y)

I guess I don't really get this ! and ? business. Wrapping, unwrapping, optional types. What is this in Java or C# terms?

Upvotes: 1

Views: 353

Answers (1)

Greg
Greg

Reputation: 9178

This will work, assuming node.scene is never nil, and node.parent is never nil:

let cameraPositionInScene = node.scene!.convertPoint(node.position, fromNode: node.parent!)

var y = CGFloat(node.parent!.position.y - cameraPositionInScene.y)

let x = CGFloat(node.parent!.position.x - cameraPositionInScene.x)

If it is possible for those to be nil, use this code instead:

if let cameraPositionInScene = node.scene?.convertPoint(node.position, fromNode: node.parent!) {
    if let parent = node.parent {
        var y = CGFloat(parent.position.y - cameraPositionInScene.y)

        let x = CGFloat(parent.position.x - cameraPositionInScene.x)

        // push the camera a bit up
        y -= 75

        parent.position = CGPointMake(x, y)
    }
}

This will test to ensure that none of the values are nil, and will do nothing if they are (instead of crashing, as the first example would).

For an explanation of how optionals work, read Apple's article.

Upvotes: 2

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