Dynamically generate object field of generic type

Question

Code:

objectType request = factory.create<objectType>();

public class factory
{
    public static T create<T>() where T : new()
    {
      T obj = new T();
      PropertyInfo propertyInfo = obj.GetType().GetProperty("client_no");
      propertyInfo.SetValue(obj, CLIENT_NUMBER, null);
      return (T)Convert.ChangeType(obj, typeof(T));
     }
}

Explanation:

I am creating a generic factory fn() that sets 2 object properties.

These properties are consistent throughout all the objects I am wanting to initialize.

1) How I call my function

objectType request = factory.create<objectType>(); // <-- This works

1b) From here if I wanted, I could do the following, but is extra code that is repetitive throughout all my objects

request.client_no = CLIENT_NUMBER;

2) Below is my factory fn()

public static T create<T>() where T : new()
{
  T obj = new T();      

  // Here is where I am having trouble setting client_no I will explain in #3         

  return (T)Convert.ChangeType(obj, typeof(T)); // <-- This works returns generic type
}

3) I have tried PropertyInfo to set the object properties as follows

PropertyInfo propertyInfo = obj.GetType().GetProperty("client_no");
propertyInfo.SetValue(obj, CLIENT_NUMBER, null);

I have also tried this

obj.GetType().GetProperty("client_no").SetValue(obj, CLIENT_NUMBER, null); 

And I have tried

T obj = new T();      
var t = typeof(T);
var prop = t.GetProperty("client_no");
prop.SetValue(obj, CLIENT_NUMBER);

4) Here is the error that I am receiving

Object reference not set to an instance of an object

More/Newer information:

So with further research. The 3rd party objects properties do not have getters and setters {get; set;} which is why the GetType() & SetValue() do not work.

My co-worker pointed out that the property is a single assignment which is why we can do

request.client_no = CLIENT_NUMBER;

So my question is how do I set these properties?

Answer 1

Using reflection, you can do something like this:

public objectName updateAccountData(int accountId, Dictionary<string,string> accountData)
{
    var request = new objectName();
    var t = typeof(objectName);
    foreach (var k in accountData)
    {
        var prop = t.GetProperty(k.Key);   // you might want to check property exists before trying to set it
        prop.SetValue(request,k.Value);
    }
    return request;
}

This assumes that your objectName class already has all the properties you need to populate.

Note that reflection is slower than directly accessing a property, so if this code is in a performance critical section of your application, it might be a problem (profile it). A couple of obvious optimization could be applied pretty easily. For example, you could store all the PropertyInfo objects retrieved from GetProperty in a Dictionary<string,PropertyInfo> to avoid having to keep looking them up. More complicated, you can actually use expression trees to build and compile expressions for property access.

For a field just substitiute t.GetField(k.Key) for GetProperty.

If you don't know if it's a field or a property (or have a mix of both), then you could use GetMember and then examine the MemberType to decide.

Answer 2

I see the accepted answer but, here is another way which doesn't involve calling reflection directly and instead uses DLR.

  public static T create<T>() where T : new()
  {
     T obj = new T();
     ((dynamic)obj).client_no = CLIENT_NUMBER;
     return obj;
  }

MSDN Dynamic Language Runtime Overview

The essential part here is that instead of writing the reflection calls yourself the compiler will take care of it. The link above discusses the benefits of using this over making reflection call directly.

Answer 3

SOLVED. Here's how.

My main issue was a miss-understanding, The item I was trying to set was not a property, but rather a field.

To better understand the difference yourself you can check out this.

Here is how I fixed it:

I set the field types of the generic

public static T create<T>() where T : new()
{
  T obj = new T();

  Type myType = typeof(T);
  FieldInfo myFieldInfo = myType.GetField("client_no");
  myFieldInfo.SetValue(obj, CLIENT_NUMBER);                        

  return obj;
}

Special thanks to @MattBurland which led me in the right direction.