C#: Using reflection with COM objects

Yesterday, I was trying to use reflection to access some properties of a COM object but was getting the following exception:

Object reference not set to an instance of an object

Debugging into, I noticed that GetProperty() method was returning null in the following call:

var propertyInfo = comObject.GetType().GetProperty("PropertyName")

After some searching, I found that we need to use the more generic InvokeMember() method to get or set the properties of a COM object. Here’s the simplest example of the usage:

//get the value of comObject.PropertyName
object propertyValue = comObject.GetType().InvokeMember("PropertyName", System.Reflection.BindingFlags.GetProperty, null, comObject, null);

//set the value of comObject.PropertyName
comObject.GetType().InvokeMember("PropertyName", System.Reflection.BindingFlags.SetProperty, null, comObject, new object[] { propertyValue });

I hope this post helps someone who is trapped into the same situation.

Article Posted: AutoCompleteComboBox for Silverlight

I have posted an article at CodeProject on customization of the Silverlight AutoCompleteBox to be used as a type-ahead ComboBox in LOB applications at CodeProject. The AutoCompleteComboBox can be used in typical Object-to-Object associations (one that we typically encounter when creating associations in Entity Framework) as well as Foreign Key associations (the new association type introduced with Entity Framework 4).

Here’s a sample usage of the control in a typical MVVM scenario:

• Object to Object Association:

  Example data structure:
  

  public class SalesOrderDetail
  {
      Product product;
      public Product Product
      {
          get { return product; }
          set { product = value; }
      }
  }
  

  Example control usage:
  

   <custom:AutoCompleteComboBox
     SelectedItemBinding="{Binding Product, Mode=TwoWay}"
     ItemsSource="{Binding Path=Products, Source={StaticResource ViewModel}}"
   />
  

• Foreign Key Association:

  Example data structure:
  

  public class SalesOrderDetail
  {
      int productID;
      public int ProductID
      {
          get { return productID; }
          set { productID = value; }
      }
  }
  

  Example control usage:
  

   <custom:AutoCompleteComboBox
     SelectedValue="{Binding ProductID, Mode=TwoWay}"
     SelectedValuePath="ProductID"
     ItemsSource="{Binding Path=Products, Source={StaticResource ViewModel}}"
   />
  

To view the implementation details, you can read the full article at :
http://www.codeproject.com/KB/silverlight/AutoComplete_ComboBox.aspx

The source code along with a demo project can be downloaded from the article as well as here (28 KB). Remember to rename the file as zip for extraction.