General Code Outline: Minimum Code, Strongest Framework, Optimal Logic

1. The appearance of an extension method greatly simplifies the amount of code

Similar to GetComponent, our custom extension method also adds some necessary logic to it as needed.

//Extension Method
//Static Class->Static Method->Parameter List First is: this type parameter
public static class ExpandClass {

    /// <summary>
    /// Get Instances
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="t"></param>
    /// <returns></returns>
    public static T GetInstance<T>(this T t,string s) where T : new()
    {
        if (t == null)
        {
            t = new T();
        }
        UnityEngine.Debug.Log(s);
        return t;
    }
}

test

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ExpandTest : MonoBehaviour {
    List<string> listA;
    // Use this for initialization
    void Start () {
        List<string> listB = listA.GetInstance("listB");
        List<string> listC = listA;
        string msg1 = listB == null ? "listB is null,bad method!" : "listB isn't null,good method!";
        string msg2 = listC == null ? "listC is null,please assignment!" : "listC isn't null,go!";
        OnDebug(msg1);
        OnDebug(msg2);
    }
    void OnDebug(string msg)
    {
        Debug.Log("Result: " + msg);
    }
}

Result

2. Generic singletons inherited from MonoBehaviour

(Reproduced from: http://blog.csdn.net/honey199396/article/details/48827955 unity3D - single generic template)
Requirements met: a, ensure that script instances are directly available through code; b, the script instances are unique in the scene; c, the script can use methods built into UnityEngine (Start, Update, etc.)

• Generic singleton

using UnityEngine;

public class SingleTon<T>: MonoBehaviour where T :MonoBehaviour {
    private static T instance;//Instance set to private for better encapsulation
    private static object lockThread = new object();//Thread lock for data security
    private static bool isQuit = false;//Type has no instances after being destroyed
    public static T GetInstance//Getting instances from attributes
    {
        get
        {
            if (isQuit)
            {
                return null;
            }
            lock (lockThread)
            {
                if (instance == null)
                {
                    instance = (T)Object.FindObjectOfType(typeof(T)); //Find first, no more new game objects, Add
                    if (Object.FindObjectsOfType(typeof(T)).Length > 1)
                    {
                        Debug.LogWarning("Too manay " + typeof(T).ToString());//If there is more than one instance, warn and return to the first
                        return instance;
                    }
                    if (instance == null)
                    {
                        GameObject singleTon = new GameObject("SingleTon",typeof(T));
                        instance = singleTon.GetComponent<T>();
                        DontDestroyOnLoad(singleTon); //Load does not destroy, depending on requirements, this sentence can be erased
                    }
                }
                return instance;
            } 
        }
    }
    public static void OnDestroy()
    {
        isQuit = true;
    }
}

• Actual Needed Singleton Class
  Hang up or hang up

using UnityEngine;

public class SingleTonTest : SingleTon<SingleTonTest> {

    //Just test, if the method is called, output it
    public void OnPrint()
    {
        Debug.Log(typeof(SingleTonTest).ToString());
    }
}

• Calls from other classes to singleton classes
  Hang on Game Object

using UnityEngine;

public class SingleTonTest1 : MonoBehaviour{

    public void Start()
    {
        SingleTonTest.GetInstance.OnPrint();
    }
}

• test result