Cannot use a lambda expression as an argument to a dynamically dispatched operation

问题

I'm trying to perform the following

int myObject = getValues(someVar).Sum(x => Int32.Parse(x.Price))

The function looks this:

List<dynamic> getValues(string something) {...}

This is the error I'm receiving: "Cannot use a lambda expression as an argument to a dynamically dispatched operation"

How can I SUM the values of a List object in a chained call similar to LINQ SUM?

回答1:

Your code works. The problem you are having isn't in the code you posted. This code runs.

void Main() {
    int myObject = getValues("12").Sum(x => Int32.Parse(x.Price));
    Console.WriteLine (myObject);
}

List<dynamic> getValues(string something) {
    var item = new { Price = something };
    IEnumerable<dynamic> items = Enumerable.Repeat<dynamic>(item, 2);
    return items.ToList();
}

This produces the output 24. The problem may be related to type inference, but that's just a guess. You should include enough code to reproduce the error for a more reliable answer.

回答2:

As mentioned in the comment, this code is working fine for me:-

public static void Main()
{
     var result = GetData("test").Sum(x => int.Parse(x.Name));
     Console.WriteLine(result);
}

    public static List<dynamic> GetData(string x)
     {
         List<dynamic> data = new List<dynamic>
         {
             new { Id =1, Name ="1"},
             new { Id =2, Name ="4"},
             new { Id =3, Name ="5"}
         };
         return data;
     }

I am getting 10 as output.

回答3:

so it ultimately turned out the issue was that I was passing a dynamic variable into the function call and subsequently using LINQ/lambda. Seems like that's a compiler no-no...

dynamic someVar = new {a=1,b=2};

int myObject = getValues(someVar.a).Sum(x => Int32.Parse(x.Price))

回答4:

Your getValues method is returning a dynamic, not a List<dynamic>. Either change your method signature or construct a new List<dynamic>(...) from its results.

dynamic list = new [] {new{Price = "1"},new{Price = "2"}};

// This produces the error you're describing:
Console.WriteLine(list.Sum(x => Int32.Parse(x.Price)));

// This works.
Console.WriteLine(new List<dynamic>(list).Sum(x => Int32.Parse(x.Price)));

来源：https://stackoverflow.com/questions/29754042/cannot-use-a-lambda-expression-as-an-argument-to-a-dynamically-dispatched-operat

标签

linq

dynamic

lambda