Question

I have a method call expression and try to invoke the method. I figured out a way, but I have problems in retrieving the parameter values since not every argument is described with a ConstantExpression.

Expression<Action<T>> = t => t.DoSomething(Par0, Par1, Par2); MethodCallExpression methodCallExpression = selector.Body                                                 as MethodCallExpression;  // get the information which is needed to invoke the method from the provided  // lambda expression. MethodInfo methodInfo = methodCallExpression.Method; object[] arguments = methodCallExpression.Arguments.OfType<ConstantExpression>()                             .Select(p => p.Value).ToArray();  // invoke the expression on every item within the enumerable foreach (TSource item in source) {      methodInfo.Invoke(item, arguments); } 

Additionally, I have seen some other ways to invoke the method, now I’m not sure what is the right way to do it.

var func = expression.Compile(); var success = func.Invoke(); 

So my question is, how can I retrieve the method argument values from methodCallExpression.Arguments?

Or is there an easier way to achieve my goal?

Answer 1

You don’t need to worry about retrieving the arguments and calling the MethodInfo yourself, you can let .NET do it for you. All you need to do is create a Lambda expression containing that method.

eg.

MethodCallExpression expression = GetExpressionSomeHow(); object result = Expression.Lambda(expression).Compile().DynamicInvoke(); 

That’s how I deal with nested queries in my Linq provider anyway.

EDIT: Actually, it looks like you might already have a LambdaExpression in the selector variable. In that case, you should be able to just compile and invoke it directly:

object result = selector.Compile().DynamicInvoke();