我有一个相当复杂的问题。我试图从方法及其正式和实际参数中获取唯一键。该方法的目标是进行方法调用，并根据以下内容返回唯一键：1）类和方法的名称以及2）调用它的参数的名称和值。
这个方法看起来像这样（对所有的细节都很抱歉，但是我找不到一个合理的方法来让这个例子更小但仍然可以解释我的问题）
public class MethodKey
{
public static string GetKey<T>(Expression<Func<T>> method, params string[] paramMembers)
{
var keys = new Dictionary<string, string>();
string scope = null;
string prefix = null;
ParameterInfo[] formalParams = null;
object[] actual = null;
var methodCall = method.Body as MethodCallExpression;
if (methodCall != null)
{
scope = methodCall.Method.DeclaringType.FullName;
prefix = methodCall.Method.Name;
IEnumerable<Expression> actualParams = methodCall.Arguments;
actual = actualParams.Select(GetValueOfParameter<T>).ToArray();
formalParams = methodCall.Method.GetParameters();
}
else
{
// TODO: Check if the supplied expression is something that makes sense to evaluate as a method, e.g. MemberExpression (method.Body as MemberExpression)
var objectMember = Expression.Convert(method.Body, typeof (object));
var getterLambda = Expression.Lambda<Func<object>>(objectMember);
var getter = getterLambda.Compile();
var m = getter();
var m2 = ((System.Delegate) m);
var delegateDeclaringType = m2.Method.DeclaringType;
var actualMethodDeclaringType = delegateDeclaringType.DeclaringType;
scope = actualMethodDeclaringType.FullName;
var ar = m2.Target;
formalParams = m2.Method.GetParameters();
//var m = (System.MulticastDelegate)((Expression.Lambda<Func<object>>(Expression.Convert(method.Body, typeof(object)))).Compile()())
//throw new ArgumentException("Caller is not a method", "method");
}
// null list of paramMembers should disregard all parameters when creating key.
if (paramMembers != null)
{
for (var i = 0; i < formalParams.Length; i++)
{
var par = formalParams[i];
// empty list of paramMembers should be treated as using all parameters
if (paramMembers.Length == 0 || paramMembers.Contains(par.Name))
{
var value = actual[i];
keys.Add(par.Name, value.ToString());
}
}
if (paramMembers.Length != 0 && keys.Count != paramMembers.Length)
{
var notFound = paramMembers.Where(x => !keys.ContainsKey(x));
var notFoundString = string.Join(", ", notFound);
throw new ArgumentException("Unable to find the following parameters in supplied method: " + notFoundString, "paramMembers");
}
}
return scope + "¤" + prefix + "¤" + Flatten(keys);
}
private static object GetValueOfParameter<T>(Expression parameter)
{
LambdaExpression lambda = Expression.Lambda(parameter);
var compiledExpression = lambda.Compile();
var value = compiledExpression.DynamicInvoke();
return value;
}
}
然后，我有以下测试，它可以正常工作：
[Test]
public void GetKey_From_Expression_Returns_Expected_Scope()
{
const string expectedScope = "MethodNameTests.DummyObject";
var expected = expectedScope + "¤" + "SayHello" + "¤" + MethodKey.Flatten(new Dictionary<string, string>() { { "name", "Jens" } });
var dummy = new DummyObject();
var actual = MethodKey.GetKey(() => dummy.SayHello("Jens"), "name");
Assert.That(actual, Is.Not.Null);
Assert.That(actual, Is.EqualTo(expected));
}
但是，如果我将() => dummy.SayHello("Jens")调用放在变量中，则调用失败。因为我不再在我的GetKey方法中获得MethodCallExpression，而是FieldExpression（MemberExpression的子类。测试是：
[Test]
public void GetKey_Works_With_func_variable()
{
const string expectedScope = "MethodNameTests.DummyObject";
var expected = expectedScope + "¤" + "SayHello" + "¤" + MethodKey.Flatten(new Dictionary<string, string>() { { "name", "Jens" } });
var dummy = new DummyObject();
Func<string> indirection = (() => dummy.SayHello("Jens"));
// This fails. I would like to do the following, but the compiler
// doesn't agree :)
// var actual = MethodKey.GetKey(indirection, "name");
var actual = MethodKey.GetKey(() => indirection, "name");
Assert.That(actual, Is.Not.Null);
Assert.That(actual, Is.EqualTo(expected));
}
Dummy类SayHello方法定义是微不足道的：
public class DummyObject
{
public string SayHello(string name)
{
return "Hello " + name;
}
public string Meet(string person1, string person2 )
{
return person1 + " met " + person2;
}
}
我有两个问题：
indirection发送到MethodKey.GetKey，并将其作为MethodCallExpression类型？MemberExpression，我如何获得所提供方法的名称和价值？我在代码的“else”部分尝试了几个，但没有成功。任何帮助表示赞赏。
在此先感谢，并为长篇文章感到抱歉。
问题是你把它放入错误的变量类型。您的方法需要Expression<Func<T>>，并且您使用的是Func<string>类型的变量来存储它。以下应该可以解决您的问题：
Expression<Func<string>> foo = () => dummy.SayHello("Jens");
var actual = MethodKey.GetKey<string>(foo, "name");
converting a .net Func<T> to a .net Expression<Func<T>>讨论了Func和Expression<Func>之间的差异以及两者之间的转换，并且一眼就看出它没有。编译器将它们变成完全不同的东西。所以在编译时使它成为正确的东西，它应该工作正常。
如果这不是一个选项，那么可能是一个带Func而不是Expression的重载可能对你有用。
请注意，在这两种情况下，我都会直接传递变量，而不是尝试将其变为调用中的新表达式。