.NET (Core and Framework)

Re: Using reflection modify List type class member...

15-Oct-08 17:13

Hi
I am trying to modify class instance members using reflection. I am having problem when trying to add/remove/display elements related to List<int> member.

Following is the code.

[CODE]

    class TestClass
    {
        public int i = 0;

        public int IValue
        {
            get
            {
                return i;
            }
            set
            {
                i = value;
            }

        }
        public List<int> m_intList = new List<int>();
    }
    class Program
    {
        static void Main(string[] args)
        {
            TestClass tcObject = new TestClass();
            tcObject.i = 1;
            tcObject.m_intList.Add(1);
            tcObject.m_intList.Add(2);

            // Following code modifies the field "I".
            {
                FieldInfo fieldInfo = tcObject.GetType().
                                        GetField(
                                        "i",
                                        BindingFlags.Static |
                                        BindingFlags.Instance |
                                        BindingFlags.NonPublic |
                                        BindingFlags.Public);

                fieldInfo.SetValue(tcObject, 2);

                System.Console.WriteLine("I value '{0}'", fieldInfo.GetValue(tcObject));
            }

            // Following code modifies the IValue property.
            {
                PropertyInfo propertyInfo = tcObject.GetType().
                                        GetProperty(
                                        "IValue",
                                        BindingFlags.Static |
                                    BindingFlags.Instance |
                                    BindingFlags.NonPublic |
                                    BindingFlags.Public);

                MethodInfo propertySetMethodInfo =
                                propertyInfo.GetSetMethod(true);

                propertySetMethodInfo.Invoke(tcObject, new Object[] { 3 });

                System.Console.WriteLine("Property IValue '{0}'", tcObject.i);
            }

            // Following is the actual problem I am having. I would like to add
            // elements to the List member m_intList.
            {
                FieldInfo fieldInfo = tcObject.GetType().
                                        GetField(
                                        "m_intList",
                                        BindingFlags.Static |
                                        BindingFlags.Instance |
                                        BindingFlags.NonPublic |
                                        BindingFlags.Public);

                // HOW do I add elements to m_intList using the fieldInfo object.
                // I am trying to use reflection to modify values for the members.

// In my actual application I do not know the type i.e. whether it is List<int> or List<string> etc

// I will just have the tcObject. From the tcOBject I will get FieldInfo object corresponding to m_intList. Using this FieldINfo, // I should be able to add or remove elements.
                foreach (int intItem in tcObject.m_intList)
                {
                    System.Console.WriteLine("List Item value '{0}'", intItem);
                }
            }
        }
    }
</string></int></int></int>

[/CODE]

Thanks
Chandra

modified on Thursday, October 16, 2008 1:56 AM

chandrap16-Oct-08 3:54

Re: Using reflection modify List type class member...

16-Oct-08 3:54

At compile time I do not know whether the type is List<int> or List<string>. At runtime I should interpret it from the fieldInfo.FieldType.

chandrap16-Oct-08 4:24

Re: Using reflection modify List type class member...

16-Oct-08 4:24

I even tried the following code

MethodInfo addMethodInfo = fieldInfo.FieldType.GetMethod("Add");
object[] intValue = { 5 };
addMethodInfo.Invoke(tcObject, new Object[] { 5 });

But the above code gives me error "Unhandled Exception: System.Reflection.TargetException: Object does not match target type." when executing the "invoke"

led mike16-Oct-08 4:41

Re: Using reflection modify List type class member...

16-Oct-08 4:41

chandrap wrote:
I am trying to modify class instance members using reflection.

Why?

led mike

chandrap16-Oct-08 4:50

Re: Using reflection modify List type class member...

16-Oct-08 4:50

Its a requirement in my application. Given an instance of class and values for the members, we should be able to update the members with the corresponding values.

led mike16-Oct-08 5:34

Using reflection modify Generic type List<int> class member...</int>

16-Oct-08 5:34

chandrap wrote:
Given an instance of class and values for the members, we should be able to update the members with the corresponding values.

Where in there is the requirement to use Reflection?

led mike

chandrap16-Oct-08 5:49

DataTable PrimaryKey problem

16-Oct-08 5:49

Hello everyone, thanks for your help. I was able to find the solution for my requirement. Following is the code

    class ListElement
    {
        public ListElement()
        {
            m_element = 0;
        }

        public ListElement(int element)
        {
            m_element = 1;
        }

        public int m_element;
    }

    class TestClass
    {
        public int i = 0;

        public int IValue
        {
            get
            {
                return i;
            }
            set
            {
                i = value;
            }

        }
        public List<int> m_intList = new List<int>();
        public List<listelement> m_lstElement = new List<listelement>();
    }
    class Program
    {
        static void Main(string[] args)
        {
            TestClass tcObject = new TestClass();
            tcObject.i = 1;
            tcObject.m_intList.Add(1);
            tcObject.m_intList.Add(2);
            tcObject.m_lstElement.Add(new ListElement(1));

            // Following code modifies the field "I".
            {
                FieldInfo fieldInfo = tcObject.GetType().
                                        GetField(
                                        "i",
                                        BindingFlags.Static |
                                        BindingFlags.Instance |
                                        BindingFlags.NonPublic |
                                        BindingFlags.Public);

                fieldInfo.SetValue(tcObject, 2);

                System.Console.WriteLine("I value '{0}'", fieldInfo.GetValue(tcObject));
            }

            // Following code modifies the IValue property.
            {
                PropertyInfo propertyInfo = tcObject.GetType().
                                        GetProperty(
                                        "IValue",
                                        BindingFlags.Static |
                                    BindingFlags.Instance |
                                    BindingFlags.NonPublic |
                                    BindingFlags.Public);

                MethodInfo propertySetMethodInfo =
                                propertyInfo.GetSetMethod(true);

                propertySetMethodInfo.Invoke(tcObject, new Object[] { 3 });

                System.Console.WriteLine("Property IValue '{0}'", tcObject.i);
            }

            {
                FieldInfo fieldInfo = tcObject.GetType().
                                        GetField(
                                        "m_intList",
                                        BindingFlags.Static |
                                        BindingFlags.Instance |
                                        BindingFlags.NonPublic |
                                        BindingFlags.Public);

                MemberInfo[] listMemberInfoArray = tcObject.GetType().GetMember("m_intList");
                MemberInfo listMemberInfo = listMemberInfoArray[0];
                MethodInfo addMethodInfo = fieldInfo.FieldType.GetMethod("Add");
                object[] elementValue = { 5 };
                addMethodInfo.Invoke(fieldInfo.GetValue(tcObject), elementValue);

                foreach(int currElement in tcObject.m_intList)
                {
                    System.Console.WriteLine("INt List element {0}", currElement);
                }

                Console.WriteLine();
            }

            {
                FieldInfo fieldInfo = tcObject.GetType().
                                        GetField(
                                        "m_lstElement",
                                        BindingFlags.Static |
                                        BindingFlags.Instance |
                                        BindingFlags.NonPublic |
                                        BindingFlags.Public);

                MethodInfo addMethodInfo = fieldInfo.FieldType.GetMethod("Add");
                Object listElementObject = Activator.CreateInstance(fieldInfo.
                                                            FieldType.
                                                            GetGenericArguments()[0]);

                FieldInfo listElementFieldInfo = listElementObject.GetType().
                                        GetField(
                                        "m_element",
                                        BindingFlags.Static |
                                        BindingFlags.Instance |
                                        BindingFlags.NonPublic |
                                        BindingFlags.Public);

                listElementFieldInfo.SetValue(listElementObject, 2);

                object[] elementValue = { listElementObject };
                addMethodInfo.Invoke(fieldInfo.GetValue(tcObject), elementValue);


                foreach (ListElement currListElement in tcObject.m_lstElement)
                {
                    System.Console.WriteLine("List Item value '{0}'", currListElement.m_element);
                }
            }

        }
    }
</listelement></listelement></int></int>

Simulation in c#

Sareh khanoom15-Oct-08 5:59

Sareh khanoom

15-Oct-08 5:59

Hello,
This might be an easy question! But I was wondering if there is any library in .net for simulation?
If I want to simulate a Network of a few computer nodes in C#, what is the best way?

Thanks a lot for your help. Smile | :)

Re: Simulation in c#

Dave Kreskowiak15-Oct-08 7:08

Dave Kreskowiak

15-Oct-08 7:08

Sareh khanoom wrote:
But I was wondering if there is any library in .net for simulation

Nope. This would have to be provided by you or some other third party library.

Sareh khanoom wrote:
If I want to simulate a Network of a few computer nodes in C#, what is the best way?

That's determined by your simulation requirements. You'll have to limit this by asking yourself "What aspects of a network are am I going to simulate and for what purpose?"

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

calhuskerfan14-Oct-08 11:54

14-Oct-08 11:54

I have a database which has a unique primary key defined key on two columns, in the example below the columns are type and data.

type	value	data
9	0	'ABC'
9	0	'ABC '

When I read in a datatable and then set the PrimaryKey collection with the designated columns I get an exception saying that 'These columns don't currently have unique values'.

So, to me it appears that ADO is ignoring the spaces with respect to determining uniqueness (although the whitespace appears in the rows collection).

I started looking into the DataTable and DataColumn object to see if there was anything that jumped out, but nothing so far.

Can anyone confirm this behavior and/or offer any assistance?

Thanks!

led mike15-Oct-08 5:01

15-Oct-08 5:01

calhuskerfan wrote:
I have a database

calhuskerfan wrote:
So, to me it appears that ADO is

ADO is NOT a database. If you are setting up the keys and constraints in the database it is the database product that will contain your answer not ADO.

led mike

calhuskerfan15-Oct-08 9:17

15-Oct-08 9:17

The constraints in the database are fine. They allow the described scenario where 'ABC' and 'ABC ' are considered unique.

When I read, with ADO, from the database into a datatable object ADO does not bring along the primary key identified in the database. So it allows at this point the two above rows to exist.

When I set the PrimaryKey property on the DataTable object (after the rows have been read) to include the column containing the above data I get the constraint exception.

Edit - The exception is actually an ArgumentException stating that the values are not unique.

led mike15-Oct-08 9:58

15-Oct-08 9:58

calhuskerfan wrote:
The constraints in the database are fine. They allow the described scenario where 'ABC' and 'ABC ' are considered unique.

What database are you using? I cannot reproduce that behavior using SQL Express 2005.

led mike

calhuskerfan15-Oct-08 10:03

15-Oct-08 10:03

Sybase SQL Anywhere 10.

Thanks.

calhuskerfan15-Oct-08 10:17

15-Oct-08 10:17

Here is a very quick (and sloppy) example that reproduces the behavior.

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Data;


namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            Test1();
        }

        public static void Test1()
        {
            DataTable dt1 = new DataTable();
            //
            dt1.Columns.Add("col0");
            dt1.Columns.Add("col1");
            dt1.Columns.Add("col2");
            //
            dt1.Columns[0].DataType = typeof(Int32);
            dt1.Columns[1].DataType = typeof(String);
            dt1.Columns[2].DataType = typeof(String);
            //
            DataRow dr = dt1.NewRow();
            dr["col0"] = 1;
            dr["col1"] = "Column 2";
            dr["col2"] = "Column 3";
            dt1.Rows.Add(dr);
            //
            dr = dt1.NewRow();
            dr["col0"] = 1;
            dr["col1"] = "Column 2";
            dr["col2"] = "Column 3   ";
            dt1.Rows.Add(dr);
            //
            try
            {
                dt1.PrimaryKey = new DataColumn[] { dt1.Columns[0], dt1.Columns[2] };
            }
            catch (ArgumentException ae)
            {
                MessageBox.Show(ae.Message);
            }
        }
    }
}

led mike15-Oct-08 10:49

15-Oct-08 10:49

calhuskerfan wrote:
Here is a very quick (and sloppy) example that reproduces the behavior.

You didn't understand my post. Using SQL Express 2005 with a Table1 designed as your example with the two column primary key constraint.

One row in the table as follows:

Type   Value  Data                                               
------ ------ -------------------------------------------------- 
1      2      ABC

Executing the following SQL

insert into Table1 (Type, Value, Data) VALUES(1, 3, 'ABC ')

Produces this error:

Cannot insert duplicate key row in object 'dbo.Table1' with unique index 'IX_Table1'.

led mike