如何在c#中确定匿名函数参数？

Question

鉴于以下代码,

    public T Execute<T>(Func<T> methodParam)
    {
        return methodParam ();
    }

    public void CallMethodsAnonymously<T>()
    {
        T result =  Execute(() => _service.SomeMethod1());
        T result1 = Execute(() => _service.SomeMethod2(someParm1));
        T result2 = Execute(() => _service.SomeMethod3( someParm1, someParm2));
    }

从Execute方法,是否可以检查"methodParam"并提取或确定匿名函数体内的参数数量？例如,是否可以从Execute方法中确定someParam1和someParam2的值？

Answer 1

您可以使用ExpressionAPI 执行此操作:

public static T Execute<T>(Expression<Func<T>> methodParam)
{
    var methodCallExpression = methodParam.Body as MethodCallExpression;
    var method = methodCallExpression.Method;
    var parameters = method.GetParameters();

    return methodParam.Compile()();
}

parameters变量将是一个ParameterInfo包含所需信息的对象数组.最后,Compile方法实际上将Expression转换为可执行委托.C#编译器还允许您使用标准lambdas/anonymous方法调用带有委托的方法的常规约定来调用此方法.

编辑:

我还注意到你想要一种方法来获得someParam1和someParam2 的实际值.这是你如何做到这一点:

private static object GetValue(Expression expression)
{
    var constantExpression = expression as ConstantExpression;
    if (constantExpression != null)
    {
        return constantExpression.Value;
    }

    var objectMember = Expression.Convert(expression, typeof(object));
    var getterLambda = Expression.Lambda<Func<object>>(objectMember);
    var getter = getterLambda.Compile();
    return getter();
}


private static object[] GetParameterValues(LambdaExpression expression)
{
    var methodCallExpression = expression.Body as MethodCallExpression;
    if (methodCallExpression != null)
    {
        return methodCallExpression.Arguments.Select(GetValue).ToArray();
    }

    return null;
}

所以现在在你的execute方法中,如果你这样做:

public static T Execute<T>(Expression<Func<T>> methodParam)
{
    var methodCallExpression = methodParam.Body as MethodCallExpression;
    var method = methodCallExpression.Method;
    var parameters = method.GetParameters();

    var values = GetParameterValues(methodParam);
    return methodParam.Compile()();
}

那么值将是一个对象[],其中包含传入的所有实际值.