Reflection - Creating class at runtime throwing error

Question

User-1343058805 posted

Hi All,

I have a abstract class and bunch of concrete classes implementing the abstract class. This scenario is working fine in normal class creation but requirement has changed. As per new requirement concrete class should be generated at runtime, I am using following code:

namespace NSUser.Entity
{
public abstract class testApprover
{

      protected testApprover nextLevel;
      public int UserID { get; set; }
     public string UserName { get; set; }

    public testApprover()
    { }

   public void SetNextLevel(testApprover nLevel)
   {
      this.nextLevel= nLevel;
    }

   public virtual string ProcessQuery(Job job, enumAction action)
   {
        ......
    }
}

public AssemblyBuilder CreateObject()
{
   AssemblyName assemblyName = new AssemblyName();
   assemblyName.Name = "DynamicReflect";
   AppDomain thisDomain = AppDomain.CurrentDomain;
   asmBuilder = thisDomain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.RunAndSave);
   modBuilder = asmBuilder.DefineDynamicModule(asmBuilder.GetName().Name, "DynamicLib.dll");

   TypeBuilder typeBuilder = null;
   DataSet ds = createTable();
   Type generetedType = null;
   string cName = null;
   foreach (DataRow dr in ds.Tables[0].Rows) //class names are coming from database
   {
      cName = dr["WFClassName"].ToString();
      var classType = new CodeTypeDeclaration(dr[0].ToString());
     classType.Attributes = MemberAttributes.Public;
     classType.BaseTypes.Add("NSUser.Entity.testApprover");

     typeBuilder = modBuilder.DefineType(dr[0].ToString(),
     TypeAttributes.Public |
     TypeAttributes.Class |
     TypeAttributes.AutoClass |
    TypeAttributes.AnsiClass |
    TypeAttributes.BeforeFieldInit |
    TypeAttributes.AutoLayout,
    typeof(NSUser.Entity.testApprover),null);

    Type[] ctorParams = new Type[] {};
    generetedType = typeBuilder.CreateType();

  }

  foreach (DataRow dr in ds.Tables[0].Rows)
 {
     Type _typeName = asmBuilder.GetType(dr["WFClassName"].ToString());
     object ptInstance = Activator.CreateInstance(_typeName);
    ((testApprover)ptInstance).UserName = "test";

    PropertyInfo prop = _typeName.GetProperty("UserName");
   prop.SetValue(((testApprover)ptInstance).UserName, "test");
THROWING FOLLOWING ERROR:
An unhandled exception of type 'System.Reflection.TargetException' occurred in mscorlib.dll
Additional information: Object does not match target type.
}
return asmBuilder;
}

Goal is to create a following concrete class 

namespace NSUser.Entity
{
class Initiator : testApprover
{

}
}

testApprover _initiator = new Initiator() { UserName = "testuser" };

Please let me know how to resolve/achieve this using reflection.

Thanks

Sham

Answer 1

User-1343058805 posted

After making some changes, receiving following error.

Additional information: Non-static method requires a target.

Please let me know how to resolve.

Answer 2

User-219423983 posted

Hi sham,

About the error “Object does not match target type”, you should just replace

prop.SetValue(((testApprover)ptInstance).UserName, "test");

with

prop.SetValue(((testApprover)ptInstance), "test");

in your code. According to the following link, the first parameter represents an object whose property value will be set. So, here it should be an instance of a class.

https://msdn.microsoft.com/en-us/library/hh194291(v=vs.110).aspx

In your latest reply, you got error “Non-static method requires a target“, could you show which line happens the error and what did you change?

I hope it’s useful to you.

Best Regard,

Weibo Zhang

Answer 3

User-1343058805 posted

Hi Zhang,

Thanks for your input, it worked I am able to assign the properties for each object coming from the database.

Currently I have configuration to create 3 classes dynamically (above code) and returning created assembly to the caller.

RuntimeObject runObj = new RuntimeObject();
AssemblyBuilder runObject = runObj.CreateObject();   <--- returning above created assembly --->

I do see all classes created previously in runObject, when I try to access one of the class property getting following error:

((testApprover)runObject.GetTypes()[0]).UserName
Cannot convert type 'System.Type' to 'NSUser.Entity.testApprover'

Thanks

Sham

Answer 4

User-1343058805 posted

Storing instance of each class in a list resolve the issue.

Thanks for the help. Greatly appreciate for the time spent to answer my question.

Answer 5

User-1343058805 posted

Hi All,

Thanks a lot for all your help, I am stuck at final step. How to invoke SetNextLevel method from created instance on above code.

Type _typeName = asmBuilder.GetType(dr["WFClassName"].ToString());
object ptInstance = Activator.CreateInstance(_typeName);

-- nextLevel is protected, when I do following assignment returning ERROR

((testApprover)ptInstance ).SetNextLevel ="new class instance"
Cannot assign to 'SetNextLevel' because it is a 'method group'   <-- ERROR

Thanks
Sham