Delegate: Method name expected error

问题:

I'm trying to get the following simple Delegate example working. According to a book I've taken it from it should be ok, but I get a Method name expected error.

namespace TestConsoleApp
{
    class Program
    {
        private delegate string D();

        static void Main(string[] args)
        {
            int x = 1;

            D code = new D(x.ToString());

        }
    }
}

Any help?

回答1:

Remove the ():

D code = new D(x.ToString);

You want to specify the method, not execute it.

回答2:

I think you mean:

D code = new D(x.ToString);

Note the lack of brackets. With the brackets on, it was a method invocation - i.e. you were trying to execute x.ToString() in that line of code. Without the brackets, it's a method group - an expression which tells the compiler to look at the available methods with that name (in that context), precisely for the purpose of creating delegates.

Which book are you using? If it really has the brackets in the examples it shows, you may want to email the author (or at least check the book's errata page). If it's C# in Depth, I'll go and cry in a corner...

回答3:

You need to feed a method into the delegate constructor.

x.ToString()

is not a method, but a string. Use

D code = new D(x.ToString); 

回答4:

Try taking the brackets off the end of the method, you are passing the method, hence don't need to use the brackets.

回答5:

D code = new D(x.ToString);   // Note the: ()

You need to pas the method to be executed in the delegate. What that you're doing is passing the value instead of the signature of the function.

回答6:

Should be:

D code = new D(x.ToString);