单利模式

全局唯一在别的类中不能被实例化，但是能全局被调用。

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


/// <summary>
/// 第一种单利模式写法
/// </summary>
public class GameController : MonoBehaviour
{
    public static GameController instance;
    private void Awake()
    {
        instance = this;
    }
}
/// <summary>
/// 第二种单利模式的写法
/// </summary>
public class GameData
{
    public static GameData instance;
    public static GameData GetInstance()
    {
        if (instance == null)
        {
            instance = new GameData();
        }
        return instance;
    }
}
/// <summary>
/// 第三种写法
/// </summary>
/// <typeparam name="T"></typeparam>
public abstract class GameTemplate<T> where T : new()
{
    private static T instance;
    public static T Instance
    {
        get
        {
            if (instance == null)
            {
                instance = new T();
            }
            return instance;
        }
    }
}
/// <summary>
/// 第四种写法
/// </summary>
/// <typeparam name="T"></typeparam>
public abstract class Singleton<T> : MonoBehaviour where T : MonoBehaviour
{
    private static T instance;
    public static T Instance
    {
        get
        {
            return instance;
        }
    }
    protected virtual void Awake()
    {
        instance = this as T;
    }
}
/// <summary>
/// 第五种
/// 同一时间内部分，程序只有一个线程进入实例化，后来的需要排队等待前一个结束
/// 增加了额外开销，损失性能，但是可保证线程安全
/// </summary>
public sealed class ThreadSingleton
{
    static ThreadSingleton instance = null;
    private static readonly object padlock = new object();
    private ThreadSingleton()
    {
    }
    public static ThreadSingleton Instance
    {
        get
        {
            lock (padlock)
            {
                if (instance == null)
                {
                    instance = new ThreadSingleton();
                }
            }

            return instance;
        }
    }
}