javascript singleton

Question

hi! i am trying to implement singleton class but i am totally confused.

i made a class that i want to use in my project it goes something like this (this is the simplified version):

class EControl{

  var state : boolean;

  //constructor
  function EControl(){
    state=false;
  }

  function getState() : boolean{
    return state;
  }

}

so i later on i realized that i need to have to access object of this class in more then one script and has to be the same object so the value that is set is the same. i was looking what is available in the forums and i found two resources. this one i dont understand http://www.unifycommunity.com/wiki/index.php?title=AManagerClass and this one is not working (i get "there is no instance") http://forum.unity3d.com/viewtopic.php?p=388784#388784

so i would appreciate if someone could explain how to make this work and how to use one object of this class in two separate scripts.

thank you!

Answer 1

Here is a simple example with comments:

class EControl {

 // This is the singleton instance that is shared with everyone.
 private static var Instance : EControl;

 // Everything that needs to get the singleton
 // instance, calls this function to get it.
 public static function GetInstance() : EControl
 {
     if (Instance == null)
         // This is the first time the function was called.  Need to
         // construct the shared instance.
         Instance = new EControl();
     return Instance;
 }

  var state : boolean ;

  // Private constructor.  This is what forces the class
  // to be a singleton since the only way to construct it
  // is via GetInstance().
  // NOTE:  Private constructors are not normally allowed
  // in JavaScript.  But it is OK in Unity.
  private function EControl()
  {
     state=false;
  }

  function GetState() : boolean
  {
    return state;
  }

}

You get instances of the singleton as follows:

private var control : EControl;

function Start() { control = EControl.GetInstance(); Debug.Log(control.GetState()); // The next line would cause a compile time error due to // the constructor's protection level. // control = new EControl(); }

javascript singleton

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