如何从 lambda 表达式构造 Action<T>？

Question

我有这个代码：

public static Tween.TweenExecuter To<T>(ref this T thisArg, T to, float time, EasingType easing = EasingType.Linear,
    TweenType type = TweenType.Simple, Func<bool> trigger = null, Action callback = null) where T : struct
{
    Tween.TweenElement<T> tween = new Tween.TweenElement<T>() 
        {
            from = thisArg,
            Setter = x => thisArg = x,
            to = to,
            time = time,
            easing = easing,
            type = type,
            Trigger = trigger,
            Callback = callback
        };

        tween = t;


    return new Tween.TweenExecuter(tween);
}

Setter 应分配给 Action<T>，但编译器报错：错误 CS1628：无法在匿名方法、lambda 表达式或查询表达式中使用 ref 或 out 参数“thisArg”

否则我该如何使用Action<T>？

编辑：

这是类型声明：

public abstract class BaseTween
{
    public float time;
    public float currentTime;
    public EasingType easing;
    public TweenType type;
    public bool deleteAtEnd = false;
    public Func<bool> Trigger;
    public Action Callback;
}

public class TweenElement<T> :BaseTween
{
    public Action<T> Setter;
    public T from;
    public T to;

}

Answer 1

您可以删除 ref 关键字并将其替换为不同形式的间接寻址，例如一个容器类。在此示例中，我创建了一个名为 Ref 的容器类，该类仅用于保存另一个值。

class Ref<T>
{
    public T Value { get; set; }

    public Ref(T item)
    {
        Value = item;
    }

    public override string ToString()
    {
        return Value.ToString();
    }

    public static implicit operator T(Ref<T> source)
    {
        return source.Value;
    }
}

我仍然不能再通过引用传递任何东西，但是如果我传递一个Ref 对象，该方法可以更新它的属性。

public class Program
{
    static Ref<Foo> _container = new Ref<Foo>(null);

    static void MyMethod(Ref<Foo> thisArg) 
    {
        Action action = () => thisArg.Value = new Foo("After");
        action();
    }

    public static void Main()
    {
        _container.Value = new Foo("Before");
        Console.WriteLine("Value before  call is: {0}", _container);
        MyMethod(_container);
        Console.WriteLine("Value after call is: {0}", _container);
    }
}

输出：

Value before call is: Before
Value after call is: After

查看DotNetFiddle 上的工作示例。

编辑：要将解决方案放入您的代码中，您的代码可能如下所示：

public static Tween.TweenExecuter To<T>(this Ref<T> thisArg, T to, float time, EasingType easing = EasingType.Linear, TweenType type = TweenType.Simple, Func<bool> trigger = null, Action callback = null) where T : struct
{
    Tween.TweenElement<T> tween = new Tween.TweenElement<T>() 
    {
        from = thisArg,
        Setter = x => thisArg.Value = x,
        to = to,
        time = time,
        easing = easing,
        type = type,
        Trigger = trigger,
        Callback = callback
    };

    return new Tween.TweenExecuter(tween);
}