How To interact with a dialog window in c#?

Hi I'm trying to write automation that will test a web-page with C#.
I'm using selenium web driver but it cannot interact with native windows.
The code need to automatically upload a file by interacting with a Dialog window,
so I'm trying to use C# code to control a dialog window.

I have managed to get a handle on the window using the following code:

public const int WM_SYSCOMMAND = 0x0112;
public const int SC_CLOSE = 0xF060;
public const int WM_SETTEXT = 0x000C;
private void ChooseFile()
{
    // retrieve the handler of the window
    int iHandle = FindWindow("#32770", "File Upload");

    if (iHandle > 0)
    {
       //Choose File - using a string with the file path
       //Press OK
    }
}

What I need to do next is to choose the file to upload and then press OK to approve.

Help will be much appreciated!

Tags: C#