Unity Android back button problem

In my unity 4.3.4f1, the back button seems doesn't work. Sometimes, we want to make back button goes to the home screen or menu without exiting the application. There is a way to do this by simply calling android native code.

At first, we can use Input.GetKeyDown(KeyCode.Escape) to detect the back button input. I wrote the code inside update function:

// We also can write it in FixedUpdate function or whatever . The point is we want to check if the user press the back button
void Update()
{
   if (Input.GetKeyDown(KeyCode.Escape)) 
   { 
      // Do your code here . . .
   }
}


Now we want to execute what happens if user press the back button. Here is the common situation:
1. Quit the application
2. Go back to menu screen

1. Quit the application

This is pretty straight forward. We can simply call Application.Quit();

2. Go back to menu screen

This is common if you want to build game for android. You can call the android native code to do this. Add a macro to make sure you run it in android.

// Inside "Do your code here . . ."

#if UNITY_ANDROID

   // Get the unity player activity

   AndroidJavaObject activity = 

      new AndroidJavaClass("com.unity3d.player.UnityPlayer")

      .GetStatic<AndroidJavaObject>("currentActivity");

   // call activity's boolean moveTaskToBack(boolean nonRoot) function

   // documentation:
http://developer.android.com/reference/android/app/Activity.html#moveTaskToBack(boolean)

   activity.Call<bool>("moveTaskToBack", true);

#endif

activity.Call<bool>("moveTaskToBack", true); The method signature is it takes parameter boolean and it returns boolean. So our call function signature must match the moveTaskToBack signature.