Final script for integrating Google Play Games and Game Center into a Unity game

SocialFeatures.cs

using UnityEngine;
using UnityEngine.SocialPlatforms;
#if UNITY_ANDROID
using GooglePlayGames;
using GooglePlayGames.BasicApi;
#endif

public class SocialFeatures : MonoBehaviour {
	
	void Start () {
		// Authenticate and register a ProcessAuthentication callback
		// This call needs to be made before we can proceed to other calls in the Social API

		#if UNITY_ANDROID
		PlayGamesPlatform.Activate();
		#endif
		Social.localUser.Authenticate (ProcessAuthentication);
	}

	// This function gets called when Authenticate completes
	// Note that if the operation is successful, Social.localUser will contain data from the server. 
	void ProcessAuthentication (bool success) {
		if (success) DontDestroyOnLoad(gameObject);
	}

	public static void ShowLeaderboard(){
		if(Social.localUser.authenticated) Social.ShowLeaderboardUI();
	}
	public static void ShowAchievements(){
		if(Social.localUser.authenticated) Social.ShowAchievementsUI();
	}
	public static void ReportLeaderboard(long score, string leaderboard){
		if(Social.localUser.authenticated) Social.ReportScore (score, leaderboard, success => {});
	}
	public static void ReportAchievement(string achievementID, double progress){
		if(Social.localUser.authenticated) Social.ReportProgress(achievementID, progress, stuff=>{});
	}
}