Using reflection modify List type class member...

Question

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);
                }
            }
        }
    }
[/CODE]

Thanks
Chandra

Alan · Answer

Here's a simple way to do it which relies on the fact that List implements the non-generic interface IList from which it gets an Add() method. As this Add method takes an object as a parameter it will work with both List and List : using System.Collections; //......... FieldInfo fieldInfo = tcObject.GetType(). GetField( m_intList BindingFlags.Static | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public); IList list = (IList)fieldInfo.GetValue(tcObject); list.Add(3); list.Add(4);

Chandra · Answer

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 m_intList = new List (); public List m_lstElement = new List (); } 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); } } } }

Chandra · Answer

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

Chandra · Answer

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

Alan · Answer

Well as things stand you can add elements to the list with the following code: FieldInfo fieldInfo = tcObject.GetType(). GetField( m_intList BindingFlags.Static | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public); List list = (List )fieldInfo.GetValue(tcObject); list.Add(3); list.Add(4); When you say you don't know what kind of list it is in your actual application is this because the field is of type List where T is a type parameter of the containing class or because it's of type List ?