title: Make SKSpriteNode subclass using Swift
body: <p>I'm trying to create class which is a subclass of SKSpriteNode and I want to add other properties and functions to it. But in the first step I faced an error.
  Here's my code:</p>
  
  <pre><code>import SpriteKit
  
  class Ball: SKSpriteNode {
      init() {
          super.init(imageNamed: "ball")
      }
  }
  </code></pre>
  
  <p>It's not a compile error, It's run-time error. It says: <code>Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)</code> and <code>fatal error: use of unimplemented initializer 'init(texture:)' for class Project.Ball</code>.</p>
  
  <p>How can I fix it?</p>