创建表达式以使用out参数调用方法

我正在尝试创建一个调用内部方法的表达式，内部方法有一个out参数，这可能吗？

public class Program { static void Main(string[] args) { var type = typeof (Program); var methodInfo = type.GetMethod("ValidateActiveControl", BindingFlags.Instance | BindingFlags.NonPublic); var p1 = Expression.Parameter(type, "program"); var p2 = Expression.Parameter(typeof (bool), "validatedControlAllowsFocusChange"); var invokeExpression = Expression.Call(p1, methodInfo, p2); var func = (Func)Expression.Lambda(invokeExpression, p1, p2).Compile(); var validatedControlAllowsFocusChange = true; // I would expect validatedControlAllowsFocusChange to be false after execution... Console.WriteLine(func.Invoke(new Program(), validatedControlAllowsFocusChange)); Console.WriteLine(validatedControlAllowsFocusChange); } internal bool ValidateActiveControl(out bool validatedControlAllowsFocusChange) { validatedControlAllowsFocusChange = false; // Some code here... return true; } } 

Answer 1

除了Jim关于MakeByRefType的观点之外，您还需要创建自定义委托类型，因为Func不支持ref或out参数。 把它们放在一起：

 delegate bool ValidateDelegate(Program program, out bool validatedControlAllowsFocusChange); static void Main(string[] args) { var type = typeof(Program); var methodInfo = type.GetMethod("ValidateActiveControl", BindingFlags.Instance | BindingFlags.NonPublic); var p1 = Expression.Parameter(type, "program"); var p2 = Expression.Parameter(typeof(bool).MakeByRefType(), "validatedControlAllowsFocusChange"); var invokeExpression = Expression.Call(p1, methodInfo, p2); var func = Expression.Lambda(invokeExpression, p1, p2).Compile(); var validatedControlAllowsFocusChange = true; // I would expect validatedControlAllowsFocusChange to be false after execution... Console.WriteLine(func.Invoke(new Program(), out validatedControlAllowsFocusChange)); Console.WriteLine(validatedControlAllowsFocusChange); } 

---

编辑：这适用于.NET 4.0，但不适用于.NET 3.5。 3.5 Framework似乎不支持带有out或ref参数的lambda表达式树。 这段代码：

 delegate void RefTest(out bool test); static void Main(string[] args) { var p1 = Expression.Parameter(typeof(bool).MakeByRefType(), "test"); var func = Expression.Lambda(Expression.Constant(null), p1); } 

抛出ArgumentException“一个lambda表达式不能包含传递引用参数”。 如果不升级到.NET 4.0，我认为你不能做你想做的事。

Answer 2

根据这篇博客文章 ，您需要做：

typeof(bool).MakeByRefType();