How to access Properties of a class from a Generic Method - C#

Another possibility would be to use System.Reflection.

1. Get the PropertyInfo from the given type T with the name of the property

2. with that PropertyInfo you can use GetValue to get the corresponding value of that property.

Here is a small test programm to exemplify this:

public class ClassA
{
      public int CustID { get; set; }
      public string Name { get; set; }
}

public class ClassB
{
      public int CustID { get; set; }
     public string Age { get; set; }
}
public static void ProceesData<T>(IList<T> param1, string date1)
{
    Parallel.ForEach(param1, (currentItem) =>
    {
        // I want to aceess CustID property of param1 and pass that value to another function
        var value = typeof(T).GetProperty("CustID").GetValue(currentItem);
        Console.WriteLine("Value: " + value);
    });
}
public static void Main(string[] args)
{
    List<ClassA> test = new List<ClassA>();

    test.Add(new ClassA { CustID = 123 });
    test.Add(new ClassA { CustID = 223 });
    test.Add(new ClassA { CustID = 323 });

    ProceesData<ClassA>(test, "test");
}

EDIT

To make it a little more universal you could just pass the parameter name into the method:

public static void ProceesData<T>(IList<T> param1, string date1, string parameter)
{
    Parallel.ForEach(param1, (currentItem) =>
    {
        // I want to aceess CustID property of param1 and pass that value to another function
        var value = typeof(T).GetProperty(parameter).GetValue(currentItem);
        Console.WriteLine("Value: " + value);
    });
}

Now you can decide what parameter you want to use:

 ProceesData<ClassA>(test, "test", "Name");

or

 ProceesData<ClassB>(test, "test", "Age");

As suggested by Gusman you could speed up a little by getting the PropertyInfo just once before the loop:

PropertyInfo pi = typeof(T).GetProperty(parameter);
Parallel.ForEach(param1, (currentItem) =>
{
    // I want to aceess CustID property of param1 and pass that value to another function
    var value = pi.GetValue(currentItem);
    Console.WriteLine("Value: " + value);
});

EDIT

Apparently performance seems to be an issue for you. So here is a comparison. You can try it on your own if you have a minute to wait. If we measure on the access time of the property:

public static void ProceesDataD<T>(IList<T> param1, string date1)
{
    Parallel.ForEach(param1, (currentItem) =>
    {
        dynamic obj = currentItem;
        int custId = obj.CustID;
    });
}
public static void ProceesData<T>(IList<T> param1, string date1) where T : ICust
{
    Parallel.ForEach(param1, (currentItem) =>
    {
        var value = currentItem.CustID;
    });
}
public static void ProceesData<T>(IList<T> param1, string date1, string parameter)
{

    PropertyInfo pi = typeof(T).GetProperty(parameter);
    Parallel.ForEach(param1, (currentItem) =>
    {
        var value = pi.GetValue(currentItem);
    });
}
public static void Main(string[] args)
{
    List<ClassA> test = new List<ClassA>();
    List<A> testA = new List<A>();

    Stopwatch st = new Stopwatch();

    for (int i = 0; i < 10000; i++)
    {
        test.Add(new ClassA { CustID = 123, Name = "Me" });
        testA.Add(new A { CustID = 123, Name = "Me" });
    }       

    st.Start();
    ProceesData<ClassA>(test, "test", "CustID");
    st.Stop();
    Console.WriteLine("Reflection: " + st.ElapsedMilliseconds);

    st.Restart();
    ProceesData<A>(testA, "test");
    st.Stop();
    Console.WriteLine("Interface: " + st.ElapsedMilliseconds);

    st.Restart();
    ProceesDataD<ClassA>(test, "test");
    st.Stop();
    Console.WriteLine("Dynamic: " + st.ElapsedMilliseconds);
}

Disclaimer: use the code passages to measure the time only one at the time. Do not run the program as it is but each single test on it's own.

Introduce interface:

 interface ICust
 {
     public int CustID { get;}
 }
 class A : ICust
 {
     public int CustID { get; set; }
     public string Name{ get; set; }
 }

 class B : ICust
 {
     public int CustID { get; set; }
     public string Age { get; set; }
 }

 public void ProceesData<T>(IList<T> param1, string date1) where T : ICust
 {
     Parallel.ForEach(param1, (currentItem) =>
     {
         GetDetails(currentItem.CustID)
     });
 }

If you can't introduce interface or base class on your existing classes, another approach is to use dynamic:

public void ProceesData<T>(IList<T> param1, string date1)
{
    Parallel.ForEach(param1, (currentItem) =>
    {
          dynamic obj = currentItem; 
          int custId = obj.CustID ;
    });
}