我有一个球，我将它射向空中:它是这样初始化的:funcinitBallNode(){//TODO:CreateballnodeballNode=SKSpriteNode(imageNamed:"Ball1")//CreateaballballNode.zPosition=ZPositions.ballletoffsetFromCorner:CGFloat=20//Offsetfrombottom-leftofscreenballNode.position=CGPoint(x:frame.minX+ballNode.size.width/2+offsetFromCorner,y:fram