在.net 4中以匿名方式使用委托

Question

Been given task to upgrade some code from .net 2 written in VS2005 to .net 4 using VS2010. When trying to compile the code I'm getting the error:

Cannot convert anonymous method to delegate type 'AssignParameter' because the parameter types do not match the delegate parameter types

The code in question the compile error is pointing at is:

AssignParameter ap = delegate(Database db, DbCommand cmd)
{
  db.AddInParameter(cmd, _jobIDParameterString, DbType.Int32, jobid);
};

DatabaseHelper.LoadDataSet(ap);

So I tracked the code to the location that the delegate reference lives:

public delegate void AssignParameter(Database db, DbCommand cmd);
public class DatabaseHelper
{
    private static Database msSqlDb;

    public static DataSet LoadDataSet(AssignParameter parameter)
    {
         ...
         DbCommand command = ...
         // Assign parameter
         if (parameter != null)
         {
             parameter(msSqlDb, command);
         }
         ...
    }
}

So I've read that delegate keyword can't be used in that way

http://staceyw1.wordpress.com/2007/12/22/they-are-anonymous-methods-not-anonymous-delegates/

But still struggling to understand how to fix my issue.

I tried

• casting the delegate
• creating a new AssignParameter call but the problem there is that I don't have either Database or DbCommand objects available

Do you have any suggestions on how to fix this problem?

Answer 1

One of the types of the parameters you're using in your method refers to a different type than the delegate defines, as the error said.

This means that either, unlike the code that you posted, your actual code uses different types in one of those places, or you have multiple types for one/both of those parameters with the same name in different namespaces.

Answer 2

public class Database
{
}

public class DbCommand
{
}

public delegate void AssignParameter(Database db, DbCommand cmd);

…

AssignParameter ap = delegate(Database db, DbCommand cmd)
{
};

This code compiles fine for me, so there must be something else going on. Are you sure that the two sets of Database and DbCommand refer to the same types? And that the code inside the delegate is itself valid?