Android back button

Hello,

I'm getting mad to proper map and use de back button of android. I tried 3 codes that I found on the web and nothing. Any help?

Code (CSharp):

1. public class RrAndroidBackButton : MonoBehaviour {
2.  
3.     public static RrAndroidBackButton instance;
4.  
5.     void Awake() {
6.         if (null == instance) {
7.             instance = this;
8.             DontDestroyOnLoad(this.gameObject);
9.         } else {
10.             Destroy(gameObject);
11.         }
12.     }
13.  
14.     void FiexdUpdate () {
15.         if (Application.platform == RuntimePlatform.Android){
16.             if (Input.GetKey(KeyCode.Escape)) {
17.                 Application.Quit();
18.  
19.                 System.Diagnostics.Process.GetCurrentProcess().Kill();
20.  
21.                 AndroidJavaObject activity = new AndroidJavaClass("com.unity3d.player.UnityPlayer")
22.                         .GetStatic<AndroidJavaObject>("currentActivity");
23.                 activity.Call<bool>("moveTaskToBack", true);
24.             }
25.         }
26.     }
27. }