创建表达式以调用方法与参数出来 [英] Create expression to invoke method with out parameter

问题描述

我想创建调用的内部方法，内部方法有一个out参数的表达，这可能吗？

 公共类节目
 {
静态无效的主要（字串[] args）
 {
变种类型= ty​​peof运算（程序）; 
变种的MethodInfo = type.GetMethod（ValidateActiveControl，BindingFlags.Instance | BindingFlags.NonPublic可）; 
 
 VAR P1 = Expression.Parameter（类型，计划）; 
 VAR P2 = Expression.Parameter（typeof运算（布尔），validatedControlAllowsFocusChange）; 
 
 VAR invokeExpression = Expression.Call（P1，MethodInfo的，P2）; 
变种FUNC =（Func键<程序，布尔，布尔>）Expression.Lambda（invokeExpression，P1，P2）.Compile（）; 
 
 VAR validatedControlAllowsFocusChange = TRUE; 
 //我希望validatedControlAllowsFocusChange是执行... 
 Console.WriteLine后假（func.Invoke（新计划（），validatedControlAllowsFocusChange））; 
 Console.WriteLine（validatedControlAllowsFocusChange）; 
 
} 
 
内部布尔ValidateActiveControl（OUT BOOL validatedControlAllowsFocusChange）
 {
 validatedControlAllowsFocusChange = FALSE; 
 
 //此处是一些代码... 
 
返回真; 
} 
} 
  

解决方案

在除了吉姆的约MakeByRefType一点，你需要创建一个自定义的委托类型，因为函数功能不支持ref或out参数。全部放在一起：

 委托布尔ValidateDelegate（计划程序，OUT BOOL validatedControlAllowsFocusChange）; 
 
静态无效的主要（字串[] args）
 {
变种类型= ty​​peof运算（程序）; 
变种的MethodInfo = type.GetMethod（ValidateActiveControl，BindingFlags.Instance | BindingFlags.NonPublic可）; 
 
 VAR P1 = Expression.Parameter（类型，计划）; 
 VAR P2 = Expression.Parameter（typeof运算（布尔）.MakeByRefType（），validatedControlAllowsFocusChange）; 
 
 VAR invokeExpression = Expression.Call（P1，MethodInfo的，P2）; 
变种FUNC = Expression.Lambda&所述; ValidateDelegate>（invokeExpression，P1，P2）.Compile（）; 
 
 VAR validatedControlAllowsFocusChange = TRUE; 
 //我希望validatedControlAllowsFocusChange是执行... 
 Console.WriteLine后假（func.Invoke（新计划（），出validatedControlAllowsFocusChange））; 
 Console.WriteLine（validatedControlAllowsFocusChange）; 
 
} 
  

---

编辑：这工作在.NET 4.0中，但不是在.NET 3.5。 3.5框架似乎并不支持lambda表达式树与out或ref参数。此代码：

 委托无效RefTest（OUT BOOL试验）; 
 
静态无效的主要（字串[] args）
 {
 VAR P1 = Expression.Parameter（typeof运算（布尔）.MakeByRefType（），测试）; 
 VAR FUNC = Expression.Lambda< RefTest>（Expression.Constant（空），P1）; 
} 
  

引发ArgumentExceptionlambda表达式不能包含引用参数通行证。我不认为你可以做你想做的，而不升级到.NET 4.0。

I am trying to create an expression that invokes an internal method, the internal method has an out parameter, is this possible?

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<Program,bool, bool>)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;
    }
}

解决方案

In addition to Jim's point about MakeByRefType, you will need to create a custom delegate type, since Func does not support ref or out parameters. Putting it all together:

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<ValidateDelegate>(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);

}

---

Edit: This works in .NET 4.0, but not in .NET 3.5. The 3.5 Framework doesn't appear to support lambda expression trees with out or ref parameters. This code:

delegate void RefTest(out bool test);

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

throws an ArgumentException "A lambda expression cannot contain pass by reference parameters". I don't think you can do what you want without upgrading to .NET 4.0.

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