UnityActionのeventラッパークラス ref: http://qiita.com/iwashihead/items/dca4f721c93295ae9fe3

file0.cs

/*** 使用例 ***/
var OnDamage = new UnityActionWrapper<int>();

// ダメージ通知の関数を登録.
OnDamage += (damage) => { Player.SetDamage(damage); };

// 実際にダメージを与える
OnDamage.Invoke(100);

// ~~~ (略) ~~~

// 登録した関数を全破棄.
OnDamage.Clear();

file1.cs

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

/// <summary>
/// UnityAction拡張イベントクラス ver引数なし
/// </summary>
public class UnityActionWrapper
{
    /// <summary>
    /// イベント.
    /// </summary>
    public event UnityAction Event
    {
        add { lock (_event) _event += value; _delegates.Add(value); }
        remove { lock (_event) _event -= value; _delegates.Remove(value); }
    }
    private event UnityAction _event = () => { };
    private List<UnityAction> _delegates = new List<UnityAction>();

    /// <summary>
    /// Add 拡張演算子.
    /// </summary>
    public static UnityActionWrapper operator +(UnityActionWrapper self, UnityAction del)
    {
        lock (self._event)
        {
            self._event += del;
            self._delegates.Add(del);
        }
        return self;
    }

    /// <summary>
    /// Remove 拡張演算子.
    /// </summary>
    public static UnityActionWrapper operator -(UnityActionWrapper self, UnityAction del)
    {
        lock (self._event)
        {
            self._event -= del;
            self._delegates.Remove(del);
        }
        return self;
    }

    /// <summary>
    /// 登録されているメソッドを実行します.
    /// </summary>
    public void Invoke()
    {
        if (_event != null) _event.Invoke();
    }

    /// <summary>
    /// 登録されているメソッドを全てremoveします.
    /// </summary>
    public void Clear()
    {
        foreach (var del in _delegates)
        {
            _event -= del;
        }
        _delegates.Clear();
    }
}

/// <summary>
/// UnityAction拡張イベントクラス ver引数1
/// </summary>
public class UnityActionWrapper<T0>
{
    /// <summary>
    /// イベント.
    /// </summary>
    public event UnityAction<T0> Event
    {
        add { lock (_event) _event += value; _delegates.Add(value); }
        remove { lock (_event) _event -= value; _delegates.Remove(value); }
    }
    private event UnityAction<T0> _event = arg0 => { };
    private List<UnityAction<T0>> _delegates = new List<UnityAction<T0>>();

    /// <summary>
    /// Add 拡張演算子.
    /// </summary>
    public static UnityActionWrapper<T0> operator +(UnityActionWrapper<T0> self, UnityAction<T0> del)
    {
        lock (self._event)
        {
            self._event += del;
            self._delegates.Add(del);
        }
        return self;
    }

    /// <summary>
    /// Remove 拡張演算子.
    /// </summary>
    public static UnityActionWrapper<T0> operator -(UnityActionWrapper<T0> self, UnityAction<T0> del)
    {
        lock (self._event)
        {
            self._event -= del;
            self._delegates.Remove(del);
        }
        return self;
    }

    /// <summary>
    /// 登録されているメソッドを実行します.
    /// </summary>
    public void Invoke(T0 arg)
    {
        if (_event != null) _event.Invoke(arg);
    }

    /// <summary>
    /// 登録されているメソッドを全てremoveします.
    /// </summary>
    public void Clear()
    {
        foreach (var del in _delegates)
        {
            _event -= del;
        }
        _delegates.Clear();
    }
}

/// <summary>
/// UnityAction拡張イベントクラス ver引数2
/// </summary>
public class UnityActionWrapper<T0, T1>
{
    /// <summary>
    /// イベント.
    /// </summary>
    public event UnityAction<T0, T1> Event
    {
        add { lock (_event) _event += value; _delegates.Add(value); }
        remove { lock (_event) _event -= value; _delegates.Remove(value); }
    }
    private event UnityAction<T0, T1> _event = (arg0, arg1) => { };
    private List<UnityAction<T0, T1>> _delegates = new List<UnityAction<T0, T1>>();

    /// <summary>
    /// Add 拡張演算子.
    /// </summary>
    public static UnityActionWrapper<T0, T1> operator +(UnityActionWrapper<T0, T1> self, UnityAction<T0, T1> del)
    {
        lock (self._event)
        {
            self._event += del;
            self._delegates.Add(del);
        }
        return self;
    }

    /// <summary>
    /// Remove 拡張演算子.
    /// </summary>
    public static UnityActionWrapper<T0, T1> operator -(UnityActionWrapper<T0, T1> self, UnityAction<T0, T1> del)
    {
        lock (self._event)
        {
            self._event -= del;
            self._delegates.Remove(del);
        }
        return self;
    }

    /// <summary>
    /// 登録されているメソッドを実行します.
    /// </summary>
    public void Invoke(T0 arg0, T1 arg1)
    {
        if (_event != null) _event.Invoke(arg0, arg1);
    }

    /// <summary>
    /// 登録されているメソッドを全てremoveします.
    /// </summary>
    public void Clear()
    {
        foreach (var del in _delegates)
        {
            _event -= del;
        }
        _delegates.Clear();
    }
}

/// <summary>
/// UnityAction拡張イベントクラス ver引数3
/// </summary>
public class UnityActionWrapper<T0, T1, T2>
{
    /// <summary>
    /// イベント.
    /// </summary>
    public event UnityAction<T0, T1, T2> Event
    {
        add { lock (_event) _event += value; _delegates.Add(value); }
        remove { lock (_event) _event -= value; _delegates.Remove(value); }
    }
    private event UnityAction<T0, T1, T2> _event = (arg0, arg1, arg2) => { };
    private List<UnityAction<T0, T1, T2>> _delegates = new List<UnityAction<T0, T1, T2>>();

    /// <summary>
    /// Add 拡張演算子.
    /// </summary>
    public static UnityActionWrapper<T0, T1, T2> operator +(UnityActionWrapper<T0, T1, T2> self, UnityAction<T0, T1, T2> del)
    {
        lock (self._event)
        {
            self._event += del;
            self._delegates.Add(del);
        }
        return self;
    }

    /// <summary>
    /// Remove 拡張演算子.
    /// </summary>
    public static UnityActionWrapper<T0, T1, T2> operator -(UnityActionWrapper<T0, T1, T2> self, UnityAction<T0, T1, T2> del)
    {
        lock (self._event)
        {
            self._event -= del;
            self._delegates.Remove(del);
        }
        return self;
    }

    /// <summary>
    /// 登録されているメソッドを実行します.
    /// </summary>
    public void Invoke(T0 arg0, T1 arg1, T2 arg2)
    {
        if (_event != null) _event.Invoke(arg0, arg1, arg2);
    }

    /// <summary>
    /// 登録されているメソッドを全てremoveします.
    /// </summary>
    public void Clear()
    {
        foreach (var del in _delegates)
        {
            _event -= del;
        }
        _delegates.Clear();
    }
}