Singletons, Statics, GameObjects, and the World - Mastering Unity Scripting - page 115

27
28 //Is player input allowed
29 public bool InputAllowed = true;
30 //-----------------------------------------
31 // Use this for initialization
32 void Awake ()
33 {
34 //Check if existing instance of class exists in scene
35 //If so, then destroy this instance
36 if(instance)
37 {
38 DestroyImmediate(gameObject);
39 return;
40 }
41
42 //Make this active and only instance
43 instance = this;
44
45 //Make game manager persistent
46 DontDestroyOnLoad(gameObject);
47 }
48 //-----------------------------------------
49 }
50 //-----------------------------------------
The following are the comments on the code sample 3-14:
• Lines 10-20 : A private member instance is added to the Manager class,
which is declared as static . This means the variable is shared across all
instances of the class if there are multiple instances, as opposed to being
a variable whose value is specific to each instance. This allows each new
instance, when created, to determine whether there is any existing instance
of the class in memory. This variable is made publically accessible too via the
Instance property, which only has a get member to make it read-only.
• Lines 36-43 : Here, in the Awake event (called at object creation), the instance
variable is checked to see whether any valid instance of the class exists in the
current scene already. If it does, then the current object is deleted, because
only one instance of this class is allowed and already exists. This means the
GameManager will persist across scene changes, and there will always be only
one original instance of the object in the scene.