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

[chandramohanp]

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.

    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.
 
                foreach (int intItem in tcObject.m_intList)
                {
                    System.Console.WriteLine("List Item value '{0}'", intItem);
                }
            }
        }
    }
 

Thanks
Chandra

[chandramohanp]

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.

[chandramohanp]

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.

[chandramohanp]

I even tried the following code

                MethodInfo addMethodInfo = fieldInfo.FieldType.GetMethod("Add"); 
                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"

[Plater]

If you wanted to add the int value 1234, I would think you would invoke the Add member with a new object(){1234} as the parameter?

For example:

List<int> myList = new List<int>();
myList.Add(98);
Type tt = myList.GetType();
tt.InvokeMember("Add", BindingFlags.Default | BindingFlags.InvokeMethod, null, myList, new object[] { 1234 });
MessageBox.Show(fred.Count.ToString());
 

You could probably do something similar with the MemberInfo stuff?

[chandramohanp]

I do not have access to m_myList, I have access to only "tcObject" instance of the class. This instance has the member m_myList.

[chandramohanp]

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);
                }
            }
 
        }
    }